SOURCE_DOCUMENTS/dataset.txt

These ensemble experiments underline the importance of both spring sea ice and summer atmospheric forcing to August SIC. In summary, we find that: Spring ice conditions were mostly responsible for the summer SIC anomaly through the end of July, while the atmosphere was mainly responsible for driving SIC to a record low during August. Partitioning the impact of 2020 spring initial sea ice conditions vs. summer atmospheric forcing on the sea ice anomaly at the time of the WS sea ice minimum on August 14 (see “Methods”) attributes ~20% to the initial conditions while ~80% is the due to the atmospheric forcing. Assuming that the increasing presence over the past 40 years of thin ice and open water at the beginning of the melt season (Fig. 5c) is primarily driven by climate change and that the summer atmospheric conditions were due to internal variability, the above 20/80 partitioning provides an approximate measure of the contributions of climate change and internal variability to the 2020 event (see further discussion in “Methods”). Is this 20% climate change signal significant or not? Extreme local events such as storms, heat waves, or floods are almost always dominated by dynamics driven by internal climate variability15. For example, flooding in New York City in response to Superstorm Sandy was on the order of 20% more extreme owing to long-term sea level rise17,18, a signal of the same magnitude we have detected in the present study. Using this example as a scale, we conclude that climate change was indeed a significant contributor to sea ice loss during the summer of 2020 in the WS. Atmospheric variability in context To put 2020 WS sea ice advection into a larger scale context, we consider here the fundamental modes of Arctic atmospheric variability, i.e., the Arctic Oscillation (AO), the Arctic Dipole Mode (ADA), and the Barents Oscillation (BO)19,20. Each of these correspond to the principal components (PCs) of empirical orthogonal functions computed from monthly mean sea level pressure fields north of 30°N (Figs. 7 and S4). During January–March 2020, when sea ice was advected into the Wandel Sea, sea level pressure over the Arctic was low, with a sea level pressure pattern similar to that found in 2017 when the Beaufort Gyre reversed21,22. The resulting onshore ice motion contributed to anomalously thick ice north of Greenland. At this time, the AO and ADA were both very high (the AO was in fact a record), a situation not found in any other year over the 41-year time series. Interestingly, summer 2020 conditions show the opposite, with ice motion westward away from the WS and the AO and ADA near record negative values. It seems clear that the anomalous 2020 WS wind forcing was associated with anomalous large-scale surface wind patterns. Fig. 7: Atmospheric circulation and sea ice motion during 2020. Discussion and conclusions While primarily driven by unusual weather, climate change in the form of thinning sea ice contributed significantly to the record low August 2020 SIC in the WS. Several advection events, some relatively early in the melt season, transported sea ice out of the region and allowed the accumulation of heat from the absorption of solar radiation in the ocean. This heat was mixed upward and contributed to rapid melt during high wind events, notably between August 9 and 16. Ocean-forced melting in this area that is traditionally covered by thick, compact ice is a key finding of this study. However, in some ways this should not be surprising given that this area (like most areas of the Arctic) has experienced a long-term thinning trend. Given the long-term thinning trend and strong interannual variability in atmospheric forcing, it seems reasonable to expect that summer sea ice conditions in the WS will likely become more variable in the future. In fact, mean SIT at the start of summer in 2018 and 2019 was even thinner than in 2020, which implies that with 2020-type atmospheric forcing, we might have seen even lower August SICs in those years, relative to that observed in 2020. In other words, SIC in the WS is now poised to plunge to low summer values, given the right atmospheric forcing. So, is the LIA in trouble? The WS is a key part of the LIA, one that has recently experienced anomalous conditions. We have shown that climate change-associated thinning ice in this region is a prerequisite for the record low ice concentrations seen in August 2020. Further, the unusually high SIT at the start of 2020 suggests that a temporary replenishment of sea ice from other parts of the Arctic may do little to protect this area from eventual sea ice loss. Recent work indicates that while western and eastern sectors of the LIA have distinct physics11, they both are experiencing long-term sea ice thinning and thus are both vulnerable to the processes discussed in this study. Our work suggests a re-examination of climate model simulations in this area, since most do not predict summer 2020-level low SICs until several decades or more into the future. Given that most climate models presently feature a subgrid-scale thickness distribution23 its evolution over time in those models should be a focal point of future investigations (i.e., rather than simply focusing on grid-cell mean thickness). Coupled model simulations where atmosphere and ocean conditions are nudged to 2020 conditions would provide useful insights into the capabilities of the current generation of climate models to replicate our results. In addition, our results should be replicated with ice-ocean models using different resolutions and physics. While the WS is only one part of the LIA, our results should give us pause when making assumptions about the persistence and resilience of summer sea ice in the LIA. Currently, little is known about marine mammal densities and biological productivity in the WS and the broader LIA. Recent studies indicate there may be some transient benefits for polar bears in areas transitioning from thick multi-year ice to thinner first year ice as biological productivity in the system increases. However, this is largely the case in shallow water <300 m in depth and it is unclear if this will occur in multi-year ice regions elsewhere. The assumption that the LIA will be available as a refuge over the next century is inherently linked to projections about species’ population status, because for some species the LIA will be the last remaining summer sea ice habitat e.g. ref. 27. It is critical that future work quantify the resilience of this area for conservation and management of ice-dependent mammals under climate change. Methods Model and model configuration details PIOMAS consists of coupled sea ice and ocean model components. The sea ice model is a multi-category thickness and enthalpy distribution sea ice model which employs a teardrop viscous plastic rheology, a mechanical redistribution function for ice ridging and a LSR (line successive relaxation) dynamics solver. The model features 12 ice thickness categories covering ice up to 28 m thick. Sea ice volume per unit area h provides an “effective sea ice thickness” which includes open water (or leads) and ice of varying thicknesses. Unless otherwise noted, we refer to this quantity as sea ice thickness. The sea ice model is coupled with the Parallel Ocean Program model developed at the Los Alamos National Laboratory. The PIOMAS model domain is based on a curvilinear grid with the north pole of the grid displaced into Greenland. It covers the area north of 49°N and is one-way nested into a similar, but global, ice-ocean model. The average resolution of the model is 30 km but features its highest resolution in the Wandel Sea, with grid cell sizes on the order of 15 × 30 km. Vertical model resolution is 5 m in the upper 30 m, and less than 10 m at depths down to 100 m, a resolution that has been shown sufficient to provide a realistic representation of upper ocean heat fluxes and the NSTM. PIOMAS is capable of assimilating satellite sea ice concentration data using an optimal interpolation approach either over the whole ice-covered area or only near ice edge. In our run HIST, satellite ice concentrations are assimilated only near the ice edge (defined as 0.15 ice concentration). This means that no assimilation is conducted in the areas where both model and satellite ice concentrations are above 0.15. If the observed ice edge exceeds the model ice edge, then sea ice is added to the thinnest sea ice thickness category and sea surface temperature (SST) is set to the freezing point. If the model ice edge exceeds observations, excess ice is removed in all thickness categories proportionally. This ice-edge assimilation approach forces the simulated ice edge close to observations, while preventing satellite-derived ice concentrations (which can be biased low during the summer e.g. ref. ) from inaccurately correcting model ice concentrations in the interior of the ice pack. Ice concentrations used for assimilation are from the Hadley Centre (HadISST v1) for 1979-2006 and from the NSIDC near real time product for 2007 to present. PIOMAS also assimilates SST, using observations provided in the NCAR/NCEP reanalysis (see below for atmospheric forcing) which in turn are derived from NOAA’s OISSTv2.1 data set. SST assimilation is only conducted in the open water areas, not in the ice-covered areas to avoid introducing an additional heat source into the sea ice budget. For this study, we also conducted a number of sensitivity simulations in which no assimilation of ice concentration and SST is performed (see below). Daily mean NCEP/NCAR reanalysis data are used as atmospheric forcing, i.e., 10-m surface winds, 2-m surface air temperature, specific humidity, precipitation, evaporation, downwelling longwave radiation, sea level pressure, and cloud fraction. Cloud fraction is used to calculate downwelling shortwave radiation following Parkinson and Kellogg. Precipitation less evaporation is calculated from precipitation and latent heat fluxes provided by the reanalysis model and specified at monthly time resolution to allow the calculation of snow depth over sea ice and input of fresh water into the ocean. There is no explicit representation of melt-ponds in this version of PIOMAS. River runoff into the model domain is specified from climatology. Because of the uncertainty of net precipitation and river runoff, the surface ocean salinity is restored to a salinity climatology with a 3-year restoring constant. Surface atmospheric momentum and turbulent heat fluxes are calculated using a surface layer model that is part of the PIOMAS framework. Additional model information can be found in in Zhang and Rothrock. PIOMAS has undergone substantial validation and has been shown to simulate sea ice thickness with error statistics similar to the uncertainty of the observations. Validation results for ocean profiles for the WS are shown in S5. Sea ice mass and upper ocean heat budgets Components of the sea ice mass and upper ocean heat budgets are computed directly from model output and residuals. Fprod is calculated as Fprod = Δh/Δt – Fadv and Fbot = Fprod – Fatm-ice. All heat entering the uppermost ocean grid cell is used to melt ice until SIT = 0; however, subsurface shortwave radiation penetration and attenuation are allowed, which can warm the ocean below the uppermost grid cell. Focndyn over the upper 60 m (Eq. (1)) can be partitioned into Focndyn = Focnadv + Fdiff + Fconvect where Focnadv, Fdiff, and Fconvect are heat exchanges between the upper 60 m of the WS and the adjacent ocean via horizontal and vertical advection, horizonal and vertical diffusion, and vertical convection, respectively. Focnadv is calculated directly from model ocean temperatures and velocities, and the sum of Fdiff + Fconvect found as a residual, i.e., Fdiff + Fconvect = ΔH/Δt – Fatm-ocn − Fbot − Focnadv where ΔH/Δt is calculated directly from model temperature profiles. We find that Fdiff + Fconvect is negligible, meaning that horizontal and vertical advection terms (more formally, heat flux convergence) dominate. This is illustrated in Fig. S6, which shows a strong ocean warming within ~100 km of the north Greenland coast owing to lateral heat flux convergence. This is nearly exactly balanced (not shown) by the vertical fluxes, i.e., downwelling, in keeping with previous results. Finally, by comparing the heat budget for summer 2020 simulations with and without data assimilation (i.e., HIST vs. INIT), we find that this numerical effect produces only a negligible heat flux term and so is neglected here (it might be larger in other regions or over a longer time period of simulation). All ice mass and ocean heat budget terms are presented in units of meters of ice melt, assuming an ice density of 917 kg m−3 and latent heat of sea ice fusion of 3.293 × 105 J/kg. HIST, INIT, and ATMOS Runs The single HIST simulation uses data assimilation for the entire simulation period and is the basis for our analysis except for the sensitivity experiments described next. The INIT and ATMOS ensemble runs turn off the assimilation after May 31, 2020. For the JJA period of comparison, differences between the HIST run (which includes assimilation) and the equivalent members from the following ensemble runs (which do not include assimilation) are negligible. Attribution of drivers The INIT and ATMOS ensembles allow a partitioning of the proximate causes of the 2020 sea ice anomaly into those driven by the initial spring conditions (sea ice and ocean) and those related to the evolution of the atmosphere (winds, temperature, radiation, humidity) over the summer. To compute the relative contribution, we calculate spatially averaged SIC and SIT differences between the INIT and ATMOS ensemble medians and the HIST median at the time of the observed and simulated WS SIC sea ice minimum (August 14). The ensemble median here represents normal conditions as the reference to which conditions (sea ice for INIT, atmosphere for ATMOS) being tested are compared. The difference from HIST is considered the contribution of the respective 2020 condition, initial ice thickness for “INIT” and atmosphere for “ATMOS.” This difference in SIC (SIT) is 6.3% (0.35 m) for INIT and 31% (1.5 m) for ATMOS. Adding these differences yields a total SIC response of 37.3%, and with respective fractions for “INIT and ATMOS” yields a 17% (6.3%/37.3%) role of initial conditions and a 83% (31%/37.3%) role for the atmosphere. The impact on SIT is slightly higher with respective contributions of 19% and 81%. This partitioning can be used as a measure of the relative impacts of climate change and internal variability. Loosely following the framework of Trenberth at al. we assume atmospheric variability is governed by internal variability, and initial (i.e., spring) sea ice conditions to be driven by long-term climate change. Therefore the 20%/80% partitioning provides an approximate measure of the contributions of climate change and internal variability on the 2020 event. This separation is not perfect because atmospheric warming appears to be playing a role as evident in the fact that ATMOS ensemble members 2018/2019 both yield ice concentrations well below the 1979–2020 mean/median. The assumption that initial ice conditions are entirely due to climate change is also not entirely correct either, since internal variability also plays a role in sea ice conditions. Nevertheless, our experiments clearly show that the climate signal of thinning sea ice exerts an impact on the magnitude of internally driven extreme events in the WS. Moreover, the fact that dynamic thickening of WS spring sea ice conditions (likely the result of internal variability) did little to improve the resilience of sea ice later in the summer provides an indication that climate change-driven thinning will likely influence future events. Model uncertainties As noted, PIOMAS has undergone substantial validation with respect to sea ice thickness, volume and motion. A measure of the uncertainty of ice-mass budget terms can be obtained from a recent study that compared monthly advection and ice production terms from PIOMAS with another numerical model and estimates derived from satellite observations. Mass budget terms from the three different sources are highly correlated and provide confidence that the relationship of budget terms is correct even if their magnitudes may have error. In addition, our INIT and ATMOS model simulations incur additional uncertainties due to the lack of a direct feedback between the atmosphere and ice-ocean system. However, this problem is less severe in the summer season which is our focus here, because summer thermal contrasts are small between the marine surface and the atmosphere. Future experiments with coupled models that allow for a “replay” of observed variability will be needed to verify this. Sea Ice Outlook: 2023 August Report We thank all the groups and individuals who submitted August Outlooks in this 16th year of the Sea Ice Outlook. We also thank NSF for supporting this year's Outlook with funds from NSF award #1331083. This month we received 29 September pan-Arctic sea-ice extent forecasts. Of these, 10 included regional Alaska sea ice extent forecasts, and 7 included Antarctic sea-ice extent forecasts. The August median forecasted value for pan-Arctic September sea-ice extent is 4.60 million square kilometers with interquartile values of 4.35 and 4.80 million square kilometers, while individual forecasts range from 2.88 to 5.47 million square kilometers. We note that the lowest two forecasts predict a new record September sea-ice extent value (current record is September 2012, with a sea-ice extent of 3.57 million square kilometers), but these forecasts are outliers relative to the other contributions. The median Alaska sea-ice extent forecast is 0.44 million square kilometers and the median Antarctic sea-ice extent forecast is 17.70 million square kilometers, which would be the second lowest Antarctic September sea-ice extent on record. Three of the seven Antarctic forecasts predict a record low sea-ice extent (see below for further details). The August median forecast of 4.60 million square kilometers is slightly lower than the July median (4.66) and slightly higher than the June median (4.54). Interestingly, the interquartile range of August forecasts is slightly higher than the July interquartile range (0.45 compared to 0.36 million square kilometers), illustrating that inter-model uncertainty was not reduced between early July and early August forecasts. The August interquartile range is narrower than the June interquartile range of 0.56 million square kilometers. We also received 13 forecasts of the September Arctic sea-ice extent anomaly. The median anomaly sea-ice extent forecast is +0.17 million square kilometers, suggesting that September 2023 sea-ice extent will be slightly above the expected long term linear trend value. Anomaly forecasts range from -0.31 million square kilometers to +0.68 million square kilometers, and the interquartile range is 0.50 million square kilometers, slightly greater than the interquartile range for absolute September sea-ice extent mentioned above. Nine groups submitted supplemental materials (see: Contributor Full Reports and Supplemental Materials below). The supplemental material contents vary among the contributions, but they may include additional figures and information on methodology including (1) how the forecasts are produced; (2) number of ensemble members used in the forecasts; (3) whether and how bias-corrections are applied; (4) ensemble spread, range of forecasts, uncertainties and other statistics; and (5) whether or not post-processing was performed. This August Outlook Report was developed by lead author Mitch Bushuk, NOAA's Geophysical Fluid Dynamics Laboratory (Executive Summary, Overview of pan-Arctic forecasts), Edward Blanchard-Wrigglesworth, University of Washington (discussion of predictions from spatial fields), Walt Meier, National Snow and Ice Data Center (Discussion of current Arctic conditions); with contributions from Uma Bhatt, University of Alaska Fairbanks (Overview of Alaska regional forecasts, discussion of pan-Arctic anomaly sea-ice forecasts and ice conditions in the Bering and Chukchi seas); François Massonnet, Université catholique de Louvain (Discussion of Antarctic contributions); and with input from Matthew Fisher and the NSIDC Development Team, (statistics and graphs); Betsy Turner-Bogren and Helen Wiggins, ARCUS (report coordination and editing). Note: The Sea Ice Outlook provides an open process for those who are interested in Arctic sea ice to share predictions and ideas; the Outlook is not an operational forecast. 2023 SIO Forecasts (Pan-Attic, Alaska Region, Spatial Forecasts, and Antarctic) The August 2023 Outlook received 29 pan-Arctic contributions (Figure 1). This year's median forecasted value for pan-Arctic September sea-ice extent is 4.60 million square kilometers with interquartile values of 4.35 and 4.80 million square kilometers. This is lower than last year's August median forecast for September, but higher than the three previous years (2019–2021). The lowest sea-ice extent forecast is 2.88 million square kilometers, from UC Louvain, which would be a new record low for the satellite period (1979-present); the highest sea-ice extent forecast is 5.47 million square kilometers, from the NMEFC ArcCFPS Group, which would be the highest September extent since 2006. Two of the outlooks forecast a new record minimum September extent (UC Louvain and the AWI Consortium), with UC Louvain predicting a notable record and AWI Consortium forecasting a value close to the 2012 record low of 3.57 million square kilometers. The observed extent values are from the NSIDC Sea Ice Index (Fetterer et al., 2017), based on the NASA Team algorithm sea ice concentration fields distributed by the NASA Snow and Ice Distributed Active Archive Center (DAAC) at NSIDC (DiGirolamo et al., 2022; Meier et al., 2021). There are 12 dynamical model contributions and 17 contributions from statistical models. The dynamical models have a median forecast of 4.33 million square kilometers with an interquartile range of 4.20 to 4.70 million square kilometers (Figure 2). Compared to the dynamical models, the statistical models generally predict higher values, with a median forecast of 4.64 million square kilometers and an interquartile range of 4.48 to 4.82 million square kilometers. The Outlooks from all methods have medians and interquartile values below last year's observed September extent (4.90), with only a handful of methods yielding an extent higher than last year (Figure 2). Figure 1. Distribution of SIO contributors for August predictions of September 2023 pan-Arctic sea-ice extent. Public/citizen contributions include: Simmons and Sun, Image courtesy of Matthew Fisher, NSIDC. Figure 2. June (left), July (center), and August (right) 2023 pan-Arctic Sea Ice Outlook submissions, sorted by method. The August median of Statistical/ML method (center left in pink) is 4.64 million square kilometers and the median for Dynamic Methods (far right in green) is 4.33 million square kilometers. The flat line represents a single submission that used Mixed/Other Methods in June. There were no submissions using heuristic methods in July or August. Image courtesy of Matthew Fisher, NSIDC. Pan-Arctic Sea-Ice Extent Anomalies This is the third year that the SIO has solicited forecasts of September mean sea-ice extent anomalies. The pan-Arctic anomaly is the departure of the contributors' September extent Outlook relative to their adopted baseline trend (e.g., the trend in historical observations, model hindcasts, etc.). This is motivated by the prospect of reducing SIO extent forecast uncertainty that may originate from models having different trends, mean states, and post-processing methodologies. The 13 anomaly forecasts range from -0.31 to +0.68 million square kilometers, with four at or below and 9 above the contributors' baseline (Figure 3 top). The observed anomalies range from -1.24 (2012) to 0.79 (2006) million square kilometers (Figure 3 bottom). The pan-Arctic 2023 August SIO anomaly forecast has a median of +0.17 million square kilometers and an interquartile range of 0.50 million square kilometers. The uncertainty in the August SIO anomaly forecasts matches that in June, both of which are smaller than the large spread in July. Similar to the pan-Arctic forecasts, statistical methods generally predict higher positive anomalies than dynamical methods. Figure 3. Anomaly pan-Arctic August 2023 forecast ranked by submission (top) and observed anomalies with August forecasts (bottom). The median August 2023 forecast is 0.17 million square kilometers. Alaska Regional Forecasts The multimodel median for the August 2023 SIO forecast for the Alaska seas is 0.44 million square kilometers, and ranges from a minimum of 0.24 to a maximum of 0.81 million square kilometers (Figure 4). The dynamical model forecasts range from a minimum of 0.24 to maximum 0.81 million square kilometers with a median of 0.27 million square kilometers. The statistical model forecasts range from a minimum of 0.33 to a maximum of 0.64 million square kilometers with a median of 0.46 million square kilometers. The statistical forecasts display a smaller spread (interquartile range of 0.05) compared to the dynamical models (interquartile range of 0.48) (Figure 5). To place these in historical perspective, the September median sea-ice extent for the Alaska seas (Bering, Chukchi, and Beaufort) over 2007–2022 is 0.44 million square kilometers, making the forecast for August 2023 SIO forecast match the observed median value (see Figure 3 of 2022 Postseason SIO report). Figure 4. Distribution of SIO contributors for August estimates of September 2023 Alaska Regional sea-ice extent. Figure courtesy of Matthew Fisher, NSIDC. Figure 5. June (left), July (center), and August (right) 2023 Alaska Region Sea Ice Outlook submissions, sorted by method. The observed September 2022 sea-ice extent for the Bering-Chukchi-Beaufort seas was 0.47 million square kilometers. Figure courtesy of Matthew Fisher, NSIDC. Pan-Arctic Forecasts with Spatial Methods We received seven forecasts of September sea-ice probability (SIP), and five of ice-free date (IFD, using both a 15% and an 80% sea-ice concentration threshold). Figure 6. September sea ice probability forecasts from 7 models, the multi-model forecast (bottom middle), and the uncertainty across the forecasts, quantified as the standard deviation (bottom right). The SIP forecasts are in general similar to those in July, with a slight reduction in uncertainty. Interestingly, the forecasts show relatively high SIP values in the Laptev sea (with the exception of the IAP LASG forecast), which in recent years has often undergone significant melt. In contrast, the East Siberian 'sea ice tongue' is forecasted to mostly melt out or show reduced cover. Figure 7. Ice-free date (IFD) forecasts using a 15% SIC threshold (top row) and an 80% SIC threshold (bottom row). The IFD forecasts show that we are near the end of the melt season, with relatively small additional loss of sea ice (shown by the reduced covers of IFD during August or September). These forecasts however help understand the differences across models in their SIP forecasts above. For example, IAP LASG forecasts melt the ice cover during August around the Laptev sea, whereas other models' forecasts maintain the ice cover in this region. Regarding the IFD80 forecasts, there is forecast uncertainty regarding the SIC over the central Arctic region, with some models forecasting significant areas to remain above 80% SIC (GFDL, RASM), whereas others forecast SICs below 80% by the end of summer throughout the central Arctic (e.g., IAP LASG). This month we received two contributions of SIC and sea ice thickness (SIT) initial conditions (Figure 8). Figure 8. SIC and SIT ICs in the RASM and GFDL forecasts. While at large scale there is reasonable agreement in the SIC and SIT ICs, there are also significant differences in particular regions (especially in the Kara and East Siberian seas), which likely help explain some of the SIP and IFD forecast differences between the two models. Antarctic Forecasts Seven outlooks were received for this August call. All groups except one (NCEP-EMC) forecast below-average September mean Antarctic sea-ice extent (Figure 9). We note that the NCEP-EMC forecast is not bias corrected, and we place caution in interpreting it – especially given the increase of the predicted Antarctic sea-ice extent with lead time. On 20 August 2023, the anomaly of daily Antarctic sea-ice extent was 2.2 million square kilometers below the 1981-2020 average, according to the NSIDC sea ice index. This confirms the exceptional behavior of austral sea ice in 2023, that has been following record-low values for eight months. Last month, we stated that it was more likely than not that Antarctic sea-ice would hit a record low in September. Given the continued slow development of sea ice and the consistent sign of the forecasts, we now turn this level of confidence to "very likely". Figure 9. Time-series of observed September Antarctic sea-ice extent and June, July, August individual model forecasts. Also shown are the climatological and anomaly persistence forecasts. Current Conditions Pan-Arctic Conditions During the month of July, sea ice extent decline was near average at 93,300 sq km per day and was fairly steady through the month and near-average decline rates continued through mid-August. At the end of July, extent was 12th lowest in the 45-year satellite record. Thus, conditions were not extreme relative to recent years, but continued a trend of much lower summer extent than before 2007. Figure 10. Daily extent (based on a 5-day running average) through 14 August 2023 and comparisons to the past four years (2019-2022) and the record low minimum year of 2012. The 1981-2010 average is the dark gray line, surrounded by the inter-quartile range (medium gray) and the inter-decile range (light gray). Note: Figure 10 is from NSIDC Charctic, based on NSIDC Sea Ice Index, Fetterer et al., 2017 and the NASA Team sea-ice concentration product at NSIDC (DiGirolamo et al., 2022; Meier et al., 2021). The primary areas of loss during the month were in the Beaufort and Chukchi Seas, where the ice edge retreated far from the coast. The ice also retreated in the eastern East Siberian Sea and the Laptev Sea, though at the end of July a tongue of ice extending to near the coast in the western East Siberian Sea remained. Sea ice also extended to the coast of the Taymyr Peninsula, keeping the Northern Sea Route closed. By mid-August, the tongue of ice in the East Siberian Sea had largely eroded, but ice still remained in the proximity of the Taymyr Peninsula. Ice was beginning to clear out of the channels of the Canadian Archipelago by the end of July and by mid-August the Amundsen (southern) route through the Northwest Passage was open and the northern route was also clearing. Figure 11. Sea ice concentration for 20 August 2023 from the NSIDC Arctic Sea Ice News and Analysis, based on the NSIDC Sea Ice Index (Fetterer et al., 2017) and the NASA team sea ice concentration product at NSIDC (DiGirolamo et al., 2022; Meier et al., 2021). The 1981-2010 median ice edge location is in orange. Note: For current data, see NSIDC Arctic Sea Ice News and Analysis and NSIDC Sea Ice Index. Temperatures during July were moderate over most of the Arctic with the exception of very warm conditions in the eastern Beaufort Sea, where air temperatures at the 925 mb level of the atmosphere were up to 7 degrees C above average. Air temperatures over the Laptev Sea were 1 to 3 degrees C below average. Elsewhere, temperatures were near-average. Figure 12. July 2023 average air temperature anomaly at the 925 mb level. NOAA Physical Sciences Laboratory, Boulder, Colorado (Kalnay et al., 1996). The July sea-level pressure pattern was marked by low pressure over the Laptev Sea and high pressure centered over the Canadian Archipelago. This dipole-anomaly pattern resulted in a fairly strong pressure gradient across the central Arctic, which led to strengthened winds and greater sea ice transport from the Pacific side of the Arctic toward the Atlantic side. Figure 13. Sea level pressure for July 2023. NOAA Physical Sciences Laboratory, Boulder, Colorado (Kalnay et al., 1996). The 500 hPa ('Z500', about 5.5 kilometers up in the atmosphere) geopotential anomalies for 1 June through 16 August 2023 (calculated from the ERA5 reanalysis) show negative anomalies over the Siberian Arctic and positive anomalies over Svalbard and the CAA (Figure 14). The summer pattern of geopotential height anomalies at 500 hPa that covaries with September sea-ice extent can also help account for forecast uncertainty in SIO forecasts, with summers that have low Z500 anomalies tending to have more sea ice (and forecasts that tend to under-predict SIE) and vice versa (Blanchard-Wrigglesworth et al, 2023). In Figure 14 we show the canonical summer pattern, and the so-far (1 June—16 August) observed pattern of Z500 anomalies for summer 2023. Figure 14. (left) The regression of detrended June through September (JJAS) 500 hPa heights on detrended September sea-ice extent over 1979–2022 (in m per million square kilometers) - when central Arctic Z500 heights are low, September SIE tends to be anomalously high, and vice versa -, and (right) anomalous 1 June—16 August 2023 500 hPa heights. As we saw in July, the atmospheric pattern during the current summer is mostly orthogonal to the canonical pattern, and thus, to first order, we do not expect the current summer's circulation to strongly impact September pan-Arctic sea ice extent anomalies. Alaska Regional Conditions The seasonal cycle of daily sea-ice extent in the Alaskan seas in 2023 remained close to climatology during the melt season until mid-July. Since then, the sea-ice extent has fallen steeply, with mid-August values nearly reaching those from 2019 (Figure 15, top). The 2022 sea ice in the Chukchi was lower than mid-August values in 2023, while it was higher in 2022 than 2023 in the Beaufort. The August Alaska sea ice had lower concentrations in 2023 compared to 2022 (Figure 15, bottom). Figure 15. Daily seasonal cycle of Bering-Chukchi-Beaufort Sea Ice Extent from 2008 to present and showing the 1981-2010 median climatology (top). August 20th sea-ice concentration in 2022 (bottom left) and 2023 (bottom right). The average surface air temperature over the Arctic for this past year (October 2021-September 2022) was the 6th warmest since 1900. The last seven years are collectively the warmest seven years on record. Low pressure across the Alaska Arctic and northern Canada sustained warm summer temperatures over the Beaufort Sea and Canadian Archipelago. The Arctic continues to warm more than twice as fast as the rest of the globe, with even greater warming in some locations and times of year. 2022 Arctic sea ice extent was similar to 2021 and well below the long-term average. August 2022 mean sea surface temperatures continued to show warming trends for 1982-2022 in most ice-free regions of the Arctic Ocean. SSTs in the Chukchi Sea were anomalously cool in August 2022. Most regions of the Arctic continued to show increased ocean plankton blooms, or ocean primary productivity, over the 2003-22 period, with the greatest increases in the Eurasian Arctic and Barents Sea. Satellite records from 2009 to 2018 show increasing maritime ship traffic in the Arctic as sea ice declines. The most significant increases in maritime traffic are occurring from the Pacific Ocean through the Bering Strait and Beaufort Sea. NASA’s Oceans Melting Greenland mission used cutting-edge technology to demonstrate that rising ocean temperatures along Greenland’s continental shelf are contributing to ice loss through melting glaciers at the ice sheet’s margins. June 2022 terrestrial snow cover was unusually low over both the North American (2nd lowest in the 56-year record) and Eurasian Arctic (3rd lowest in the record). Winter accumulation was above average, but early snow melt in a warming Arctic contributed to the overall low snow cover. A significant increase in Arctic precipitation since the 1950s is now detectable across all seasons. Wetter-than-normal conditions were observed from October 2021 through September 2022, in what was the 3rd wettest year of the past 72 years. The Greenland Ice Sheet experienced its 25th consecutive year of ice loss. In September 2022, unprecedented late-season warming created surface melt conditions over 36% of the ice sheet, including at the 10,500 ft ice sheet summit. Tundra greening declined from the record high values of the previous two years, with high productivity in most of the North American Arctic, but unusually low productivity in northeastern Siberia. Wildfires, extreme weather events, and other disturbances have become more frequent, influencing the variability of tundra greenness. Striking differences were observed between lake ice durations in Eurasia and North America, with substantially longer than average ice durations in Eurasia and predominantly shorter in North America. Freeze-up of Arctic lakes is occurring later in most of North America, especially in Canada. The distribution, conservation status, and ecology of most Arctic pollinators are poorly known though these insects are critically important to Arctic ecosystems and the food systems of Arctic Indigenous Peoples and Arctic residents. Coordinated long-term monitoring, increased funding, and emerging technologies can improve our understanding of Arctic pollinator habitats and status, and inform effective conservation strategies. In 2022, despite an outbreak of highly pathogenic avian influenza affecting birds throughout North America and variable spring weather conditions, the population sizes of most Arctic geese remained high with increasing or stable trends. Multiple geese species provide food and cultural significance for many peoples. In contrast, communities in the northern Bering and southern Chukchi Sea region reported higher-than-expected seabird die-offs for the sixth consecutive year. Tracking the duration, geographic extent, and magnitude of seabird bird die-offs across Alaska’s expansive and remote coastline is only possible through well-coordinated communication and a dedicated network of Tribal, State, and Federal partners. People experience the consequences of a rapidly changing Arctic as the combined effects of physical conditions, responses of biological resources, impacts on infrastructure, decisions influencing adaptive capacities, and environmental and international influences on economics and well-being. Living and innovating in Arctic environments over millennia, Indigenous Peoples have evolved holistic knowledge providing resilience and sustainability. Indigenous expertise is augmented by scientific abilities to reconstruct past environments and to model and predict future changes. Decision makers (from communities to governments) have the skills necessary to apply this experience and knowledge to help mitigate and adapt to a rapidly changing Arctic. Addressing unprecedented Arctic environmental changes requires listening to one another, aligning values, and collaborating across knowledge systems, disciplines, and sectors of society. What is the longest river in the world? The largest river on the planet, the Amazon, forms from the confluence of the Solimões (the upper Amazon River) and the Negro at the Brazilian city of Manaus in central Amazonas. At the river conjunction, the muddy, tan-colored waters of the Solimões meet the “black” water of the Negro River. The unique mixing zone where the waters meet extends downstream through the rainforest for hundreds of miles, and attracts tourists from all over the world, which has contributed to substantial growth in the city of Manaus. It is the vast quantity of sediment eroded from the Andes Mountains that gives the Solimões its tan color. By comparison, water in the Negro derives from the low jungles where reduced physical erosion of rock precludes mud entering the river. In place of sediment, organic matter from the forest floor stains the river the color of black tea. The Solimões provides nutrient-rich mud to lakes on the floodplain (lower right). The ecology of muddy lakes differs correspondingly from that of nutrient-poor, blackwater rivers and lakes. Solimões water can be seen leaking into the Negro west of the main meeting zone (lower left). The Solimões is much shallower than the Negro because it has filled its valley and bed with great quantities of sediment since the valleys were excavated. Widths of the rivers differ for this reason Global Temperature Key Takeaway: Earth’s global average surface temperature in 2020 statistically tied with 2016 as the hottest year on record, continuing a long-term warming trend due to human activities. This graph (graph_globaltemperature.txt) shows the change in global surface temperature compared to the long-term average from 1951 to 1980. The year 2020 statistically tied with 2016 for the hottest year on record since record keeping began in 1880 (source: graph_globaltemperature.txt). NASA’s analyses generally match independent analyses prepared by National Oceanic and Atmospheric Administration (NOAA) and other institutions. The animation on the right shows the change in global surface temperatures. Dark blue shows areas cooler than average. Dark red shows areas warmer than average. Short-term variations are smoothed out using a 5-year running average to make trends more visible in this map. Methane Key Takeaway: Methane is a powerful heat-trapping gas. The amount of methane in the atmosphere is increasing due to human activities. Methane Basics Methane (CH4) is a powerful greenhouse gas, and is the second-largest contributor to climate warming after carbon dioxide (CO2). A molecule of methane traps more heat than a molecule of CO2, but methane has a relatively short lifespan of 7 to 12 years in the atmosphere, while CO2 can persist for hundreds of years or more. Methane comes from both natural sources and human activities. An estimated 60% of today’s methane emissions are the result of human activities. The largest sources of methane are agriculture, fossil fuels, and decomposition of landfill waste. Natural processes account for 40% of methane emissions, with wetlands being the largest natural source. (Learn more about the Global Methane Budget.) The concentration of methane in the atmosphere has more than doubled over the past 200 years. Scientists estimate that this increase is responsible for 20 to 30% of climate warming since the Industrial Revolution (which began in 1750). Tracking Methane Although it’s relatively simple to measure the amount of methane in the atmosphere, it’s harder to pinpoint where it’s coming from. NASA scientists are using several methods to track methane emissions. One tool that NASA uses is the Airborne Visible InfraRed Imaging Spectrometer - Next Generation, or AVIRIS-NG. This instrument, which gets mounted onto research planes, measures light that is reflected off Earth’s surface. Methane absorbs some of this reflected light. By measuring the exact wavelengths of light that are absorbed, the AVIRIS-NG instrument can determine the amount of greenhouse gases present. NASA added the Earth Surface Mineral Dust Source Investigation (EMIT) instrument to the International Space Station in 2022. Though built principally to study dust storms and sources, researchers found that it could also detect large methane sources, known as “super-emitters.” These aircraft and satellite instruments are finding methane rising from oil and gas production, pipelines, refineries, landfills, and animal agriculture. In some cases, these measurements have led to leaks being fixed, including suburban gas leaks and faulty equipment in oil and gas fields. The Arctic is a source of natural methane from wetlands, lakes, and thawing permafrost. Although a warming climate could change these emissions, scientists do not yet think it will drive a major increase. To this end, NASA’s Arctic Boreal and Vulnerability Experiment, or ABoVE, has been measuring methane coming from natural sources like thawing permafrost in Alaska and Canada. Data Notes and Sources NOAA’s methane data comes from a globally-distributed network of air sampling sites. https://gml.noaa.gov/ccgg/trends_ch4/ Ice core data are from Law Dome (Antarctica) and Summit (Greenland) ice cores, from Etheridge, D.M., L.P. Steele, R.J. Francey, and R.L. Langenfelds, Atmospheric methane between 1000 AD and present: Evidence of anthropogenic emissions and climatic variability. Journal of Geophysical Research, 103, D13, 15,979-15,993, 1998. Data archived at the Carbon Dioxide Information Analysis Center https://cdiac.ess-dive.lbl.gov/trends/atm_meth/lawdome_meth.htm Ocean Warming Ninety percent of global warming is occurring in the ocean, causing the water’s internal heat to increase since modern recordkeeping began in 1955, as shown in the upper chart. (The shaded blue region indicates the 95% margin of uncertainty.) This chart shows annual estimates for the first 2,000 meters of ocean depth. Each data point in the upper chart represents a five-year average. For example, the 2020 value represents the average change in ocean heat content (since 1955) for the years 2018 up to and including 2022. The lower chart tracks monthly changes in ocean heat content for the entire water column (from the top to the bottom of the ocean) from 1992 to 2019, integrating observations from satellites, in-water instruments, and computer models. Both charts are expressed in zettajoules. Heat stored in the ocean causes its water to expand, which is responsible for one-third to one-half of global sea level rise. Most of the added energy is stored at the surface, at a depth of zero to 700 meters. The last 10 years were the ocean’s warmest decade since at least the 1800s. The year 2022 was the ocean’s warmest recorded year and saw the highest global sea level. Ice Sheets Key Takeaway: Antarctica is losing ice mass (melting) at an average rate of about 150 billion tons per year, and Greenland is losing about 270 billion tons per year, adding to sea level rise. Data from NASA's GRACE and GRACE Follow-On satellites show that the land ice sheets in both Antarctica (upper chart) and Greenland (lower chart) have been losing mass since 2002. The GRACE mission ended in June 2017. The GRACE Follow-On mission began collecting data in June 2018 and is continuing to monitor both ice sheets. This record includes new data-processing methods and is continually updated as more numbers come in, with a delay of up to two months. This is important because the ice sheets of Greenland and Antarctica store about two-thirds of all the fresh water on Earth. They are losing ice due to the ongoing warming of Earth’s surface and ocean. Meltwater coming from these ice sheets is responsible for about one-third of the global average rise in sea level since 1993. Sea Level Key Takeaway: Global sea levels are rising as a result of human-caused global warming, with recent rates being unprecedented over the past 2,500-plus years. Sea level rise is caused primarily by two factors related to global warming: the added water from melting ice sheets and glaciers, and the expansion of seawater as it warms. The first graph tracks the change in global sea level since 1993, as observed by satellites. The second graph, which is from coastal tide gauge and satellite data, shows how much sea level changed from about 1900 to 2018. Items with pluses (+) are factors that cause global sea level to increase, while minuses (-) are what cause sea level to decrease. These items are displayed at the time they were affecting sea level. EVIDENCES How Do We Know Climate Change Is Real? There is unequivocal evidence that Earth is warming at an unprecedented rate. Human activity is the principal cause. TAKEAWAYS While Earth’s climate has changed throughout its history, the current warming is happening at a rate not seen in the past 10,000 years. According to the Intergovernmental Panel on Climate Change (IPCC), "Since systematic scientific assessments began in the 1970s, the influence of human activity on the warming of the climate system has evolved from theory to established fact."1 Scientific information taken from natural sources (such as ice cores, rocks, and tree rings) and from modern equipment (like satellites and instruments) all show the signs of a changing climate. From global temperature rise to melting ice sheets, the evidence of a warming planet abounds. The rate of change since the mid-20th century is unprecedented over millennia. Earth's climate has changed throughout history. Just in the last 800,000 years, there have been eight cycles of ice ages and warmer periods, with the end of the last ice age about 11,700 years ago marking the beginning of the modern climate era — and of human civilization. Most of these climate changes are attributed to very small variations in Earth’s orbit that change the amount of solar energy our planet receives. The current warming trend is different because it is clearly the result of human activities since the mid-1800s, and is proceeding at a rate not seen over many recent millennia.1 It is undeniable that human activities have produced the atmospheric gases that have trapped more of the Sun’s energy in the Earth system. This extra energy has warmed the atmosphere, ocean, and land, and widespread and rapid changes in the atmosphere, ocean, cryosphere, and biosphere have occurred. Earth-orbiting satellites and new technologies have helped scientists see the big picture, collecting many different types of information about our planet and its climate all over the world. These data, collected over many years, reveal the signs and patterns of a changing climate. Scientists demonstrated the heat-trapping nature of carbon dioxide and other gases in the mid-19th century.2 Many of the science instruments NASA uses to study our climate focus on how these gases affect the movement of infrared radiation through the atmosphere. From the measured impacts of increases in these gases, there is no question that increased greenhouse gas levels warm Earth in response. "Scientific evidence for warming of the climate system is unequivocal." - Intergovernmental Panel on Climate Change Ice cores drawn from Greenland, Antarctica, and tropical mountain glaciers show that Earth’s climate responds to changes in greenhouse gas levels. Ancient evidence can also be found in tree rings, ocean sediments, coral reefs, and layers of sedimentary rocks. This ancient, or paleoclimate, evidence reveals that current warming is occurring roughly 10 times faster than the average rate of warming after an ice age. Carbon dioxide from human activities is increasing about 250 times faster than it did from natural sources after the last Ice Age. As evidências para mudanças Climáticas rápidas são convincentes: A temperatura global está aumentando A temperatura média da superfície do planeta aumentou cerca de 2 graus Fahrenheit ( 1 graus Celsius ) desde o final do século XIX, uma mudança impulsionada em grande parte pelo aumento das emissões de dióxido de carbono na atmosfera e em outras atividades humanas.4 A maior parte do aquecimento ocorreu nos últimos 40 anos, sendo os sete anos mais recentes os mais quentes. Os anos de 2016 e 2020 estão empatados no ano mais quente já registrado.5 O oceano está ficando mais quente O oceano absorveu grande parte desse aumento de calor, com os 100 metros superiores ( cerca de 328 pés ) do oceano mostrando um aquecimento de 0,67 graus Fahrenheit ( 0,33 graus Celsius ) desde 1969.6 A Terra armazena 90% da energia extra no oceano. As folhas de gelo estão encolhendo As camadas de gelo da Groenlândia e da Antártica diminuíram em massa. Dados da experiência de recuperação de gravidade e clima da NASA mostram que a Groenlândia perdeu uma média de 279 bilhões de toneladas de gelo por ano entre 1993 e 2019, enquanto a Antártica perdeu cerca de 148 bilhões de toneladas de gelo por ano.7 Geleiras estão recuando As geleiras estão recuando em quase todo o mundo —, incluindo nos Alpes, Himalaia, Andes, Montanhas Rochosas, Alasca e África.8 A cobertura de neve está diminuindo Observações por satélite revelam que a quantidade de cobertura de neve na primavera no Hemisfério Norte diminuiu nas últimas cinco décadas e a neve está derretendo mais cedo. Crédito da imagem: NASA / JPL-Caltech9 O nível do mar está aumentando O nível global do mar subiu cerca de 8 polegadas ( 20 centímetros ) no século passado. A taxa nas últimas duas décadas, no entanto, é quase o dobro da do século passado e acelera um pouco a cada ano.10 Gelo do Mar Ártico está diminuindo Tanto a extensão quanto a espessura do gelo do mar do Ártico diminuíram rapidamente nas últimas décadas.11 Eventos extremos estão aumentando em frequência O número de eventos recordes de alta temperatura nos Estados Unidos tem aumentado, enquanto o número de eventos recordes de baixa temperatura vem diminuindo desde 1950. Os EUA também testemunharam um número crescente de intensos eventos de chuvas.12 A acidificação do oceano está aumentando Desde o início da Revolução Industrial, a acidez das águas superficiais do oceano aumentou cerca de 30%.13,14 Esse aumento ocorre devido ao fato de os seres humanos emitirem mais dióxido de carbono na atmosfera e, portanto, serem mais absorvidos pelo oceano. O oceano absorveu entre 20% e 30% do total de emissões antropogênicas de dióxido de carbono nas últimas décadas ( 7,2 a 10,8 bilhões de toneladas métricas por ano ).15,16 Crédito da imagem: NOAA CAUSES The Causes of Climate Change Human activities are driving the global warming trend observed since the mid-20th century. TAKEAWAYS The greenhouse effect is essential to life on Earth, but human-made emissions in the atmosphere are trapping and slowing heat loss to space. Five key greenhouse gases are carbon dioxide, nitrous oxide, methane, chlorofluorocarbons, and water vapor. While the Sun has played a role in past climate changes, the evidence shows the current warming cannot be explained by the Sun. Scientists attribute the global warming trend observed since the mid-20th century to the human expansion of the "greenhouse effect"1 — warming that results when the atmosphere traps heat radiating from Earth toward space. Life on Earth depends on energy coming from the Sun. About half the light energy reaching Earth's atmosphere passes through the air and clouds to the surface, where it is absorbed and radiated in the form of infrared heat. About 90% of this heat is then absorbed by greenhouse gases and re-radiated, slowing heat loss to space. Four Major Gases That Contribute to the Greenhouse Effect: FORCING: Something acting upon Earth's climate that causes a change in how energy flows through it (such as long-lasting, heat-trapping gases - also known as greenhouse gases). These gases slow outgoing heat in the atmosphere and cause the planet to warm. Carbon Dioxide A vital component of the atmosphere, carbon dioxide (CO2) is released through natural processes (like volcanic eruptions) and through human activities, such as burning fossil fuels and deforestation. Methane Like many atmospheric gases, methane comes from both natural and human-caused sources. Methane comes from plant-matter breakdown in wetlands and is also released from landfills and rice farming. Livestock animals emit methane from their digestion and manure. Leaks from fossil fuel production and transportation are another major source of methane, and natural gas is 70% to 90% methane. Nitrous Oxide A potent greenhouse gas produced by farming practices, nitrous oxide is released during commercial and organic fertilizer production and use. Nitrous oxide also comes from burning fossil fuels and burning vegetation and has increased by 18% in the last 100 years. Chlorofluorocarbons (CFCs) These chemical compounds do not exist in nature – they are entirely of industrial origin. They were used as refrigerants, solvents (a substance that dissolves others), and spray can propellants. Another Gas That Contributes to the Greenhouse Effect: FEEDBACKS: A process where something is either amplified or reduced as time goes on, such as water vapor increasing as Earth warms leading to even more warming. Water Vapor Water vapor is the most abundant greenhouse gas, but because the warming ocean increases the amount of it in our atmosphere, it is not a direct cause of climate change. EFFECTS The Effects of Climate Change The effects of human-caused global warming are happening now, are irreversible for people alive today, and will worsen as long as humans add greenhouse gases to the atmosphere. TAKEAWAYS We already see effects scientists predicted, such as the loss of sea ice, melting glaciers and ice sheets, sea level rise, and more intense heat waves. Scientists predict global temperature increases from human-made greenhouse gases will continue. Severe weather damage will also increase and intensify. Earth Will Continue to Warm and the Effects Will Be Profound Global climate change is not a future problem. Changes to Earth’s climate driven by increased human emissions of heat-trapping greenhouse gases are already having widespread effects on the environment: glaciers and ice sheets are shrinking, river and lake ice is breaking up earlier, plant and animal geographic ranges are shifting, and plants and trees are blooming sooner. Effects that scientists had long predicted would result from global climate change are now occurring, such as sea ice loss, accelerated sea level rise, and longer, more intense heat waves. "The magnitude and rate of climate change and associated risks depend strongly on near-term mitigation and adaptation actions, and projected adverse impacts and related losses and damages escalate with every increment of global warming." - Intergovernmental Panel on Climate Change Some changes (such as droughts, wildfires, and extreme rainfall) are happening faster than scientists previously assessed. In fact, according to the Intergovernmental Panel on Climate Change (IPCC) — the United Nations body established to assess the science related to climate change — modern humans have never before seen the observed changes in our global climate, and some of these changes are irreversible over the next hundreds to thousands of years. Scientists have high confidence that global temperatures will continue to rise for many decades, mainly due to greenhouse gases produced by human activities. The IPCC’s Sixth Assessment report, published in 2021, found that human emissions of heat-trapping gases have already warmed the climate by nearly 2 degrees Fahrenheit (1.1 degrees Celsius) since 1850-1900.1 The global average temperature is expected to reach or exceed 1.5 degrees C (about 3 degrees F) within the next few decades. These changes will affect all regions of Earth. The severity of effects caused by climate change will depend on the path of future human activities. More greenhouse gas emissions will lead to more climate extremes and widespread damaging effects across our planet. However, those future effects depend on the total amount of carbon dioxide we emit. So, if we can reduce emissions, we may avoid some of the worst effects. "The scientific evidence is unequivocal: climate change is a threat to human wellbeing and the health of the planet. Any further delay in concerted global action will miss the brief, rapidly closing window to secure a liveable future."2 SOLUTIONS - Intergovernmental Panel on Climate Change Sustainability and Government Resources NASA is an expert in climate and Earth science. While its role is not to set climate policy or prescribe particular responses or solutions to climate change, its job does include providing the scientific data needed to understand climate change. NASA then makes this information available to the global community – the public, policy-, and decision-makers and scientific and planning agencies around the world. (For more information, see NASA's role.) With that said, NASA takes sustainability very seriously. NASA’s sustainability policy is to execute its mission as efficiently as possible. In doing so, we continually improve our space and ground operations. Sustainability involves taking action now to protect the environment for both current and future living conditions. In implementing sustainability practices, NASA supports its missions by reducing risks to the environment and our communities. In executing its mission, NASA's sustainability objectives are to: increase energy efficiency; increase the use of renewable energy; measure, report, and reduce NASA's direct and indirect greenhouse gas emissions; conserve and protect water resources through efficiency, reuse, and stormwater management; eliminate waste, prevent pollution, and increase recycling; leverage agency acquisitions to foster markets for sustainable technologies and environmentally preferable materials, products, and services; design, construct, maintain, and operate high-performance sustainable buildings; utilize power management options and reduce the number of agency data centers; support economic growth and livability of the communities where NASA conducts business; evaluate agency climate change risks and vulnerabilities and develop mitigation and adaptation measures to manage both the short-and long-term effects of climate change on the agency's mission and operations; raise employee awareness and encourage each individual in the NASA community to apply the concepts of sustainability to every aspect of their daily work to achieve these goals; maintain compliance with all applicable federal, state, local or territorial law and regulations related to energy security, a healthy environment, and environmentally-sound operations; and comply with internal NASA requirements and agreements with other entities.  What is the gray circle in the middle of some of the extent maps? Not all satellites pass close enough to the North Pole for their sensors to collect data there. This lack of data is indicated by a gray circle, or “pole hole,” in each image. Created: June 2008 Related question: How will we know if ice at the North Pole melts? Return to top How will we know if ice at the North Pole melts? Historically, lack of satellite data directly over the North Pole has not concerned scientists; they have always assumed that the area underneath is covered with sea ice. However, in recent years, the possibility that there will be no sea ice over the North Pole in summer has become more likely. Fortunately, some satellite sensors are able to obtain data directly over the North Pole; Data from these satellites could be used to fill in data that are missing from other satellite records. For example, the NASA Advanced Microwave Scanning Radiometer—Earth Observing System (AMSR-E) could fill in some missing data because it has a smaller pole hole than other satellites. Or, scientists could use the NASA Moderate Resolution Imaging Spectroradiometer (MODIS) instrument, which does collect data over the North Pole and thus has no pole hole. To learn more about how scientists study sea ice, see our Learn about Sea Ice: Science page. Created: June 2008 Related questions: What is the gray circle in the middle of some of the extent maps? Will the ice at the North Pole melt? Return to top What satellite is the sea ice data from? The “Daily image update,” as well as many of the images shown in Arctic Sea Ice News & Analysis, are derived from the Sea Ice Index data product. The Sea Ice Index relies on NASA-developed methods to estimate sea ice conditions using passive-microwave data from the Defense Meteorological Satellite Program (DMSP) the Special Sensor Microwave Imager/Sounder (SSMIS). The basis for the Sea Ice Index is the data set, “Near-Real-Time DMSP SSM/I Daily Polar Gridded Sea Ice Concentrations,” and the NASA-produced “Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I Passive Microwave Data.” For more details, see the Sea Ice Index. Updated: June 2009 Return to top Why is the Sea Ice Index product used to study sea ice? The passive-microwave data used for the Sea Ice Index is especially helpful because the sensor can “see” through clouds and deliver data even during the six months of Arctic darkness and frequently cloudy conditions. Some other satellite sensors cannot penetrate clouds to take data, so the results are sporadic and dependent upon weather conditions. Still other sensors can see through clouds, but they do not cover the entire region of the globe where sea ice exists every day, making near-real-time monitoring difficult. Furthermore, some sensors cannot provide information in winter, when polar darkness prevails. The passive microwave sea ice record dates back to 1979, one of the longest environmental data sets we know of. This provides a long-term product that consistently tracks changes in the ice cover over many years, lending additional confidence to the trends that we observe. So, although NSIDC refers to additional satellite data in developing our analysis, we primarily rely on passive-microwave data for Arctic Sea Ice News & Analysis images and content, and for tracking long-term change. Created: June 2008 Return to top Sometimes readers report that our maps show ice incorrectly, compared to on-the-ground observations or other data sources. Why is this? Quality control for near-real-time-data One reason that ice extent images may have errors is that the satellite derived images in our Daily Image Update are near-real time and have not yet undergone rigorous quality control to correct for conflicting information that is especially likely along coastlines. Areas near land may show some ice coverage where there is not any because the sensor’s resolution is not fine enough to distinguish ice from land when a pixel overlaps the coast. Sometimes, the data we receive have errors in the geolocation data, caused by problems with the instrument, which could affect where ice appears. Near-real-time data may also have areas of missing data, displayed on the daily map as gray wedges, speckles, or spider web patterns. In addition, satellite sensors occasionally have problems and outages, which can affect the near-real-time data. We correct these problems in the final sea ice products, which replace the near-real-time data in about six months to a year. Despite areas of inaccuracy, near-real-time data are still useful for assessing changes in sea ice coverage, particularly when averaged over an entire month. The monthly average image is more accurate than the daily images because weather anomalies and other errors are less likely to affect it. Because of the limitations of near-real-time data, they should be used with caution when seeking to extend a sea ice time series, and should not be used for operational purposes such as navigation. To look at monthly images that have been through quality control, click on “Archived Data and Images” on the Sea Ice Index. Resolution of the data Another reason for apparent errors in ice extent is that the data are averaged over an area of 25 kilometers by 25 kilometers (16 by 16 miles). This means that the ice edge could be off by as much as 25 to 50 kilometers (16 to 31 miles) in passive-microwave data, compared to higher-resolution satellite systems. In addition, we define ice extent as any 25 by 25 kilometer grid cell with with an average of ?at least 15 percent ice. Ice-free areas may nevertheless exist within an area that is defined by our algorithms as ice covered. Passive microwave data characteristics The daily image is derived from remotely sensed passive microwave data, which can be collected even during cloudy or dark conditions. Passive microwave data may show ice where none actually exists due to signal variation between land and water along coastlines, or because of atmospheric interference from rain or high winds over the ice-free ocean. Reasons that passive microwave data may not detect ice include the presence of thin, newly formed ice; the shift in albedo of actively melting ice; and atmospheric interference. Thin, newly formed ice is consistently underestimated by these data. Centers such as the U.S. National Ice Center and the Canadian Ice Service that publish sea ice data for navigation employ higher spatial resolution data that is better able to detect such thin ice. Despite the limitations in passive microwave data, they still yield good large-scale estimates for the overall extent pattern and values of the ice. Plus, the limitations are consistent, affecting the data this year in the same way they have affected it in previous years. So when comparing from year to year, these types of errors do not affect the comparison. While passive microwave data products may not show as much detail or be as accurate “on the ground” as other satellite data, they provide a consistent time series to track sea ice extent going back to 1979. Higher resolution sensors only go back to 2002. This type of long-term, consistent data is important to scientists who study whether or not change is taking place in a system. To learn more about how scientists study sea ice, see our Learn about Sea Ice: Science page. Updated: March 2012 Related question: Do your data undergo quality control? Return to top Do your data undergo quality control? The daily and monthly images that we show in Arctic Sea Ice News & Analysis are near-real-time data. Near-real-time data do not receive the rigorous quality control that final sea ice products enjoy, but it allows us to monitor ice conditions as they develop. Several possible sources of error can affect near-real-time images. Areas near land may show some ice coverage because the sensor has a coarse resolution and though a coastal filter is applied, it is not effective in some situations. Sometimes, the data we receive have geolocation errors, which could affect where ice appears. Near-real-time data may also have areas of missing data, displayed on the daily map as gray wedges, speckles, or spider web patterns. In addition, satellite sensors occasionally have problems and outages, which can affect the near-real-time data. We correct these problems in the final sea ice products, which replace the near-real-time data in about six months to a year. Despite its areas of inaccuracy, near-real-time data are still useful for assessing changes in sea ice coverage, particularly when averaged over an entire month. The monthly average image is more accurate than the daily images because weather anomalies and other errors are less likely to affect it. Because of the limitations of near-real-time data, they should be used with caution when seeking to extend a sea ice time series, and should not be used for operational purposes such as navigation. To look at monthly images that have been through quality control, click on “Archived Data and Images” on the Sea Ice Index. Updated: June 2009 Return to top What is the error range for your images? NSIDC does not have error bars on the time series plot shown in the “Daily Image Update” and the daily time series plot (usually labeled “Figure 2”) because we strive to keep the images concise and easy to read. Plus, the error bars would be quite small compared to the total extent values in the images. We estimate error based on accepted knowledge of the sensor capabilities and analysis of the amount of “noise,” or daily variations not explained by changes in weather variables. For average relative error, or error relative to other years, the error is approximately 20,000 to 30,000 square kilometers (7,700 to 11,600 square miles), a small fraction of the total existing sea ice. For average absolute error, or the amount of ice that the sensor measures compared to actual ice on the ground, the error is approximately 50 thousand to 1 million square kilometers (19,300 to 386,100 square miles), varying over the year. During summer melt and freeze-up in the fall, the extent may be underestimated by 1 million square miles; during mid and late winter before melt starts, the error will be on the low end of the estimates. It is important to note that while the magnitude of the error varies through the year, it is consistent year to year. This gives scientists high confidence in interannual trends at a given time of year. The absolute error values may seem high, but it is important to note that each year has roughly the same absolute error value, so the decline over the long term remains clear. NSIDC has high confidence in sea ice trend statistics and the comparison of sea ice extent between years. Created: June 2008 Related questions: Sometimes readers report that our maps show ice incorrectly. Why? What is standard deviation and how does it relate to sea ice extent? Return to top Why do you use the 1981 to 2010 average for comparisons? NSIDC scientists use the 1981 to 2010 average because it provides a consistent baseline for year-to-year comparisons of sea ice extent. Thirty years is considered a standard baseline period for weather and climate, and the satellite record is now long enough to provide a thirty year baseline period. If we were to recalculate the baseline every year to incorporate the most recent year of data, we couldn’t meaningfully compare between recent years. To borrow a common phrase, we would be comparing apples and oranges. The problem with relying on a sliding average becomes clear over time, when we try to compare new years of data with previous years. For example, if we rely on a standard, unchanging baseline like 1981 to 2010, we can easily and clearly compare September 2007 and September 2008 with each other. However, if we were to use a sliding baseline of 1979 to 2006 for September 2007, and a sliding baseline of 1979 to 2007 for September 2008, we would no longer be comparing “apples to apples” when we compared the two years to the baseline. Arctic Sea Ice News and Analysis and the Sea Ice Index moved to a baseline period of 1981 to 2010 starting July 1, 2013. Previously, NSIDC had used 1979 to 2000 as the comparison period. Updated: July 2013 Related questions: What is the difference between sea ice area and extent? Are you updating the 1981-2010 average to the 1991-2020 average for comparisons? Return to top Are you updating the 1981-2010 average to the 1991-2020 average for comparisons? No. A 30-year climatology is commonly used as a reference period in weather and climate to define “normal” conditions. Thirty years is long enough to average out most natural variations in climate, like El Niño, that can affect the average in the short term. A norm or an average for weather is geared towards operational type of applications. For instance, is the weather warmer than average compared to recent years? If so, should farmers plant crops earlier than last year? Therefore, weather forecast services update their climatology with each new decade. The US National Weather Service, for instance, updated their period from 1981 to 2010 to 1991 to 2020. NSIDC scientists decided against such a shift for analyzing changes to Arctic sea ice. A shifting baseline makes tracking long-term climate change more complicated. As the baseline shifts, anomalies (amount above or below “normal”) and relative (percent per decade) trends will change. For climate, we want to look at long-term changes, so having a consistent baseline makes more sense. That way when new data is collected, there is a consistent baseline for decadal or longer evaluation of change. Ideally, this baseline period would be relatively stable and without much of a trend. This is particularly a problem for Arctic sea ice where the last 10 years have had several extremely low extents. Including these recent years hardly represents “normal” in terms of the long-term climate. If we switch to the 1991-2020 average, then all previous statistics can not be compared with the new baseline. And the new baseline will be more skewed by the downward trend. This would make relative trends, represented as percents per decade, larger in magnitude than they are with 1981-2010 average. For this reason, we plan to maintain the 1981-2010 period as our standard climate record. The period comprises the earliest three full decades in the continuous satellite record. The data for this period have been well validated and consistency has been maintained through careful calibrations between different sensors used in the time series. As a note, ASINA’s sea ice analysis tool allows users to see data relative to a customizable climatology. Updated: October 2021 Return to top The daily image update isn’t current; why? The daily image update is produced from near-real-time operational satellite data, with a data lag of approximately one day. However, visitors may notice that the date on the image is occasionally more than one day behind. Occasional short-term delays and data outages do occur and are usually resolved in a few days. Updated: February 2009 Related question: Do your data undergo quality control? Return to top Are there other sources of sea ice data? How do these sources differ from NSIDC data? Other researchers and organizations monitor sea ice independently, using a variety of sensors and algorithms. While these sources agree broadly with NSIDC data, extent measurements differ because of variation in the formulas (algorithms) used for the calculation, the sensor used, the threshold method to determine whether a region is “ice-covered,” and processing methods. NSIDC’s methods are designed to be as internally consistent as possible to allow for tracking of trends and variability throughout our data record. Links to other sources of sea ice data are listed below: University of Bremen Daily Updated AMSR-E Sea Ice Maps Nansen Environmental & Remote Sensing Center Arctic Regional Ocean Observing System Another source of sea ice data is the operational centers that provide support to ships navigating in the Arctic. There are often discrepancies between information from these centers and our data because they employ additional data sources to capture as much detail on sea ice conditions as possible. However, unlike our data, because the quality and availability of their data sources vary, their products do not provide a long-term, consistent timeseries suitable for tracking climate trends and variability. Several Arctic nations have operational sea ice centers. The two North American centers are: US National Ice Center Canadian Ice Service Updated: February 2020 Related questions: Do your data undergo quality control? What is the difference between sea ice area and extent? Return to top Why do different years appear on the graph? Each year at the beginning of January, the reference year on the daily extent graph changes. The graph of daily sea ice extent for the Northern Hemisphere shows ice extent in the current year, the 1981 to 2010 average, and the year with record low ice extent, (currently 2012). The graph has a five month window. This means that in December, the graph shows the record year of 2012, plus some of 2008 (2007-08) and 2013 (2012-13). When we shift the view in January to show five months beginning in October, the graph shows the end of 2006 and the beginning of 2007 (2006-07) and the end of 2011 and the beginning of 2012 (2011-12). July 2013 Return to top What is the standard deviation range on the daily image? In February 2010, we added the range of standard deviation to our daily extent chart. The gray area around the 1981 to 2010 average line shows the two standard deviation range of the data, which serves as an estimate of the expected range of natural variability. For the past few years, Arctic sea ice extent for most months has been more than two standard deviations below the 1981 to 2010 mean, particularly in summer. Updated: July 2013 Related questions: What is standard deviation and how does it relate to sea ice extent? What is the error range for your images? Return to top What is standard deviation and how does it relate to sea ice extent? Standard deviation is a measure of variation around a mean. One standard deviation is defined as encompassing 68% of the variation, and two standard deviations encompass 95% of the variation. Scientists use standard deviations as a way to estimate the range of variability of data. In the context of climate data like sea ice extent, it provides a sense of the range of expected conditions. Measurements that fall far outside of the two standard deviation range or consistently fall outside that range suggest that something unusual is occurring that can’t be explained by normal processes. For sea ice extent data, the standard deviation is computed for each day of the year from the extent on that day over the 30 years of the baseline period, 1981 to 2010. Doubling the standard deviation to produce a 95% range means that 95% of the daily extents for the years 1981 to 2010 fall within that range. In recent years, ice extent has declined and in the summer especially, it has regularly fallen outside of two standard deviations. This suggests that the recent decline in sea ice extent represents a significant change in conditions from 1981 to 2010 time period. Updated: July 2013 Related question: What is the error range for your images? Return to top Why don’t you publish a global sea ice extent number? The combined number, while easy to derive from our online posted data, is not useful as an analysis tool or indicator of climate trends. Looking at each region’s ice extent trends and its processes separately provides more insight into how and why ice extent is changing. Sea ice in the Arctic is governed by somewhat different processes than the sea ice around Antarctica, and the very different geography of the two poles plays a large role. Sea ice in the Arctic exists in a small ocean surrounded by land masses, with greater input of dust, aerosols, and soot than in the Southern Hemisphere. Sea ice in the Southern Hemisphere fringes an ice-covered continent, Antarctica, surrounded by open oceans. While both regions are affected by air, wind, and ocean, the systems and their patterns are inherently very different. Moreover, at any point in time, the two poles are in opposite seasons, and so a combined number would conflate summer and winter trends, or spring and autumn trends, for the two regions. Why is the daily change in sea ice extent in the northern hemisphere larger at the beginning of each month? If you plot the average daily change in sea ice extent in the northern hemisphere, based on the data from ‘Sea_Ice_Index_Daily_Extent_G02135_v3.0.xlsx,’ you may notice that at the beginning of each month, particularly in the summer, the daily change is larger. This is related to the valid ice masks that are used in the processing of the Sea Ice Index. It is really a land spillover effect: that is, even when there is not ice in a coastal sea, ice can appear to fringe the coast, and fill fjords. This happens because there are mixed land-ocean areas within the sensor’s field of view. That mixture of land and ice looks like sea ice to the algorithms interpreting the sensor data. A correction for land spillover is applied, but it is not perfect. Monthly valid ice masks are also used and these mask out areas where sea ice is not realistic in a given month, including along the coast due to land spillover. When you switch to the next month there is a change in the ice mask. Going from May to June to July, the valid ice mask moves north in the Arctic and crops out more potential ice areas south of the valid ice line. Ice may have receded in a coastal sea by the end of May, for instance, but may still appear to be along the coastline. On the first day of June the new mask removes more of the invalid ice, which is why you see a sudden change in sea ice. Updated: July 2020 Return to top STUDYING SEA ICE What would it mean for Arctic sea ice to recover? Sea ice extent normally varies from year to year, much like the weather changes from day to day. But just as one warm day in October does not negate a cooling trend toward winter, a slight annual gain in sea ice extent over a record low does not negate the long-term decline. Even though the extent of Arctic sea ice has not returned to the record low of 2012, the data show that it is not recovering. To recover would mean returning to within its previous, long-term range. Arctic sea ice extent remains very low. In addition, sea ice remains much thinner than in the past, and so is more vulnerable to further decline. While ice thickness is difficult to measure using satellites, a variety of data sources and estimates indicate that the Arctic ice cover remains thin. For more information on ice thickness, read our Ask a Scientist article, Getting beneath the ice. So what would scientists call a recovery in sea ice? First, a true recovery would continue over a period of multiple years. Second, scientists would expect to see a series of minimum sea ice extents that not only exceed the previous year, but also return to within the range of natural variation. In a recovery, scientists would also expect to see a return to an Arctic sea ice cover dominated by thicker, multiyear ice. Updated: September 2013 Return to top What was sea ice like before the satellite era? The satellite record only dates back to 1979. However, scientists have used historical records of sea ice conditions to estimate sea ice extent before 1979. For more on this topic, read the Ask a Scientist article, How was Arctic sea ice measured before the satellite era? Updated: February 2022 Related questions: Has the Arctic Ocean always had ice in summer? Return to top Has the Arctic Ocean always had ice in summer? We know for sure that at least in the distant past, the Arctic was ice-free. Fossils from the age of the dinosaurs, 65 million years ago, indicate a temperate climate with ferns and other lush vegetation. Based on the paleoclimate record from ice and ocean cores, the last warm period in the Arctic peaked about 8,000 years ago, during the so-called Holocene Thermal Maximum. Some studies suggest that as recent as 5,500 years ago, the Arctic had less summertime sea ice than today. However, it is not clear that the Arctic was completely free of summertime sea ice during this time. The next earliest era when the Arctic was quite possibly free of summertime ice was 125,000 years ago, during the height of the last major interglacial period, known as the Eemian. Temperatures in the Arctic were higher than now and sea level was also 4 to 6 meters (13 to 20 feet) higher than it is today because the Greenland and Antarctic ice sheets had partly melted. Because of the burning of fossil fuels, global averaged temperatures today are getting close to the maximum warmth seen during the Eemian. Carbon dioxide levels now are far above the highest levels during the Eemian, indicating there is still warming to come. According to analyses at NASA and NOAA, the past decade has been the warmest in the observational record dating back to the 19th century and the Arctic has been substantially higher than the global average. Updated: February 2012 Related question: How do we know human activities cause global climate change? Return to top Will the ice at the North Pole melt? Sometimes in everyday use, people associate “the North Pole” with the entire Arctic region. However, when scientists discuss the North Pole, they mean the geographic North Pole, a single point on the globe located at 90 degrees North. The term Arctic generally refers to a much larger region that encompasses the northern latitudes of the globe. The Arctic includes regions of Russia, North America, and Greenland, as well as the Arctic Ocean. The scientific community has a range of predictions concerning when we could see an ice-free Arctic Ocean in summer. Predictions range from sometime between 2030 and 2100. Updated: January 2012 Related questions: What is the gray circle in the middle of some of the extent maps? How will we know if ice at the North Pole melts? Return to top Why don’t I hear much about Antarctic sea ice? NSIDC scientists do monitor sea ice in the Antarctic, and sea ice in the Antarctic is of interest to scientists worldwide. While there are many peer-reviewed journal articles on the topic of Antarctic sea ice and its changes, it has received less attention than the Arctic. Antarctic sea ice has in general changed far less dramatically than Arctic ice. Moreover, changes in Antarctic sea ice are unlikely to have a significant direct impact on the temperate southern latitudes. For more information on Antarctic sea ice, read the Ask a Scientist article, How does Antarctic sea ice differ from Arctic sea ice? Antarctic sea ice data is available on the NSIDC Sea Ice Index. Updated: January 2012 Return to top Is wintertime Antarctic sea ice increasing or decreasing? Wintertime Antarctic sea ice is increasing at a small rate and with substantial year-to-year variation. Monthly sea ice data show trends of increasing sea ice extent that are slightly above the mean year-to-year variability over the satellite record (1979 to present). In more technical terms, the trends are statistically significant at the 95% level, although small (~1% per decade as of 2016). Global climate model projections for sea ice trends around Antarctica are at odds with what is being observed. Nearly all models to date project a slight decline in sea ice extent at present and for the next several decades. The mismatch between model results and observations is a topic of research, and a basis for investigations to find the processes that must be added to the models to align them with what is observed. However, analysis of the variability of Antarctic sea ice in models shows that it is possible that the current trend of increasing sea ice extent is a result of the high variability in the Antarctic sea ice and climate system. The dominant, though subtle, change in the climate pattern of Antarctica has been a gradual increase in the westerly circumpolar winds. Models suggest that both the loss of ozone (the ozone hole that occurs in September/October every year) and increases in greenhouse gases lead to an increase in frequency of this climate pattern. When winds push on sea ice, they tend to move it in the direction they are blowing, but the Coriolis effect adds an apparent push to the left. In the unconfined system of Antarctic sea ice, this pushes the ice northward away from the continent. By spreading sea ice westward and a little northward (and since we measure extent with a 15% cutoff) the gradual trend towards faster mean winds means a gradual trend toward spreading of the ice cover. This general pattern may be part of the explanation for the trend. Recent records of wintertime extents (in 2012, 2013, and 2014) appear to be associated with patterns in air circulation related to the westerly wind regime. The Amundsen Sea Low (ASL), a climate feature of the annual average pressure pattern for Antarctica, varies in both strength and location on a seasonal basis. The ASL tends to be stronger when westerly winds are strong. The ASL, and its effect of sea ice formation and drift, appears to be a major part of the recent string of record winter maximums. More recently (since July 2015) sea ice has returned to near-average conditions, and as of this writing is at a record daily low extent. This highlights the inherent variability in the system. However, one analysis that has attempted to explain both the very large winter extents of 2012, 2013, and 2014, and the subsequent lower and near-average winter maximums in 2015 and 2016 has suggested that the El Niño Southern Oscillation and a Pacific trend called the Pacific Decadal Oscillation (a residual tendency toward El Niño or La Niña in the Pacific that shifts on multi-decadal timescales) may be linked to the change. In other words, the advent of a strong El Niño in late 2015 and early 2016 may have shifted wind and ocean circulation to favor lower extents after a series of La-Niña-prone years (Meehl, 2016). The trend towards stronger circumpolar winds has also caused a sea ice extent decline near the Antarctic Peninsula. In general, the winds tend to dive slightly southward as they approach the Peninsula, an effect of the mountain ridges of the Andes and other circulation features in the Amundsen and Bellingshausen Sea (the ASL mentioned above). A stronger wind from the northwest brings warmer conditions and therefore less ice to the region. Lastly, the El Niño and La Niña cycle also appear to influence sea ice in the Pacific sector. El Niño patterns (a warm eastern tropical Pacific) are associated with warmer winds and less ice; the opposite is true for La Niña. Climate models suggest that the observed increases in Antarctic sea ice are not outside natural variability. However, all models indicate that the ice extent should decrease as greenhouse gases in the atmosphere increase further later in this century. For more information, read the Ask a Scientist article, How does Antarctic sea ice differ from Arctic sea ice? To see data on Antarctic sea ice, see the Sea Ice Index. Updated: December 2016 Related questions: Has the Arctic Ocean always had ice in summer? Return to top CAUSES OF GLOBAL CLIMATE CHANGE AND ICE DECLINE How do we know human activities cause climate change? Fossil fuel burning is responsible for climate change because of the way in which an increased concentration of carbon dioxide in the atmosphere alters the planet’s energy budget and makes the surface warmer. The most fundamental measure of Earth’s climate state is the globally averaged surface air temperature. We define climate change as an extended trend in this temperature. Such a change cannot happen unless something forces the change. Various natural climate forcings exist. For example, periodic changes in the Earth’s orbit about the sun alter the seasonal and latitudinal distribution of solar radiation at the planet’s surface; such variations can be linked to Earth’s ice ages over the past two million years. Changes in solar output influence how much of the sun’s energy the Earth’s surface receives as a whole; more or less solar energy means warmer or cooler global climate. Explosive volcanic eruptions inject sulfur dioxide and dust high into the stratosphere, blocking some of the sun’s energy from reaching the surface and causing it to cool. These are climate forcings because they alter the planet’s radiation or energy budget. An increase in the atmosphere’s concentration of carbon dioxide is also a climate forcing: it leads to a situation in which the planet absorbs more solar radiation than it emits to space as longwave radiation. This means the system gains energy. The globally averaged temperature will increase as a result. This is in accord with a fundamental principle of physics: conservation of energy. As humans burn fossil fuels, adding carbon dioxide to the atmosphere, globally average temperature rises as a result. Arctic Sea Ice 6th Lowest on Record; Antarctic Sees Record Low GrowthIn Brief:The annual Arctic sea ice minimum (lowest) annual extent was the sixth-lowest on record this year, while Antarctic sea ice reached its lowest maximum ever. These both continue a long-term downward trend due to human-caused global warming.Arctic sea ice likely reached its annual minimum extent on Sept. 19, 2023, making it the sixth-lowest year in the satellite record, according to researchers at NASA and the National Snow and Ice Data Center (NSIDC). Meanwhile, Antarctic sea ice reached its lowest maximum extent on record on Sept. 10 at a time when the ice cover should have been growing at a much faster pace during the darkest and coldest months.Scientists track the seasonal and annual fluctuations because sea ice shapes Earth’s polar ecosystems and plays a significant role in global climate. Researchers at NSIDC and NASA use satellites to measure sea ice as it melts and refreezes. They track sea ice extent, which is defined as the total area of the ocean in which the ice cover fraction is at least 15%.Between March and September 2023, the ice cover in the Arctic shrank from a peak area of 5.64 million square miles (14.62 million square kilometers) to 1.63 million square miles (4.23 million square kilometers). That’s roughly 770,000 square miles (1.99 million square kilometers) below the 1981–2010 average minimum of 2.4 million square miles (6.22 million square kilometers). The amount of sea ice lost was enough to cover the entire continental United States.Sea ice around Antarctica reached its lowest winter maximum extent on Sept. 10, 2023, at 6.5 million square miles (16.96 million square kilometers). That’s 398,000 square miles (1.03 million square kilometers) below the previous record-low reached in 1986 – a difference that equates to roughly the size of Texas and California combined. The average maximum extent between 1981 and 2010 was 7.22 million square miles (18.71 million square kilometers).“It’s a record-smashing sea ice low in the Antarctic,” said Walt Meier, a sea ice scientist at NSIDC. “Sea ice growth appears low around nearly the whole continent as opposed to any one region.”This year in the Arctic, scientists saw notably low levels of ice in the Northwest Passage, Meier added. “It is more open there than it used to be. There also seems to be a lot more loose, lower concentration ice – even toward the North Pole – and areas that used to be pretty compact, solid sheets of ice through the summer. That’s been happening more frequently in recent years.”Meier said the changes are a fundamental, decades-long response to warming temperatures. Since the start of the satellite record for ice in 1979, sea ice has not only been declining in the Arctic, but also getting younger. Earlier starts to spring melting and ever-later starts to autumn freeze-up are leading to longer melting seasons. Research has shown that, averaged across the entire Arctic Ocean, freeze-up is happening about a week later per decade, or one month later than in 1979.Nathan Kurtz, lab chief of NASA’s Cryospheric Sciences Laboratory at the agency’s Goddard Space Flight Center in Greenbelt, Maryland, said that as the Arctic warms about four times faster than the rest of the planet, the ice is also growing thinner. “Thickness at the end of the growth season largely determines the survivability of sea ice. New research is using satellites like NASA’s ICESat-2 (Ice, Cloud and land Elevation Satellite-2) to monitor how thick the ice is year-round.”Kurtz said that long-term measurements of sea ice are critical to studying what’s happening in real time at the poles. “At NASA we’re interested in taking cutting-edge measurements, but we’re also trying to connect them to the historical record to better understand what’s driving some of these changes that we’re seeing.”Scientists are working to understand the cause of the meager growth of the Antarctic sea ice, which could include a combination of factors such as El Nino, wind patterns, and warming ocean temperatures. New research has shown that ocean heat is likely playing an important role in slowing cold season ice growth and enhancing warm season melting.This record-low extent so far in 2023 is a continuation of a downward trend in Antarctic sea ice that started after a record high in 2014. Prior to 2014, ice surrounding the continent was increasing slightly by about 1% per decade.Sea ice melting at both poles reinforces warming because of a cycle called “ice-albedo feedback.” While bright sea ice reflects most of the Sun’s energy back to space, open ocean water absorbs 90% of it. With greater areas of the ocean exposed to solar energy, more heat can be absorbed, which warms the ocean waters and further delays sea ice growth.

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