nasa-gesdisc/es-publications-researchareas huggingface dataset:
Future Changes in Oceanography and Biogeochemistry Along the Canadian (2021)

Model projections of ocean circulation and biogeochemistry are used to investigate large scale climate changes under moderate mitigation (RCP 4.5) and high emissions (RCP 8.5) scenarios along the continental shelf of the Canadian Pacific Coast. To reduce computational cost, an approach for dynamical downscaling of climate projections was developed that uses atmospheric climatologies with augmented winds to simulate historical (19862005) and future (20462065) periods separately. The two simulations differ in initial and lateral open boundary conditions. For each simulation, the daily climatology of surface winds in the driving model was augmented with high-frequency variability from an atmospheric reanalysis product. The time-slice approach was able to reproduce the observed climate state for the historical period. Sensitivity tests confirmed that the high frequency wind variability plays an essential role in freshwater distribution in this region. Projections suggest that sea surface temperature will increase by 1.82.4C and surface salinity will decrease between 0.08 and 0.23 depending on whether a moderate or high emissions scenario is used. Stratification increases throughout the region and there is some evidence of nutrient limitation near the surface. Primary production and phytoplankton productivity (chlorophyll) also increase. Density surfaces are relocated deeper in the water column and this change is mainly driven by surface heating and freshening. Changes in saturation state are mainly due to anthropogenic CO
              2
              with minor contributions from solubility, remineralization and advection. There is little difference between RCP 4.5 and RCP 8.5 with regard to projections of deoxygenation and acidification. The depths of the aragonite saturation state and the oxygen minimum zone are projected to become shallower by  100 and  75 m respectively. Extreme states of temperature, oxygen and acidification are projected to become more frequent and more extreme, with the frequency of occurrence of
              
                
                  
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              expected to approximately double under either scenario.

Research areas: Ecosystems
Roles of Sea Surface Temperature Warming and Loss of Arctic Sea Ice in the Enhanced Summer Wetting Trend Over Northeastern Siberia During Recent Decades (2020)

The water cycle over middle- to high-latitude regions has experienced rapid changes in recent decades. The sea surface temperature (SST) and Arctic sea ice influence the water cycle over these regions, but the relative roles of SST warming and the loss of Arctic sea ice remain unclear. We identify an enhanced change in the summer (June-August) water cycle over northeastern Siberia (55-70°N, 100-170°E) during the last three decades. The driving force of this enhanced wetting trend is investigated using both observations and model simulations. An increasing trend of low-level southerly winds and a decrease in sea-level pressure are observed over northeastern Siberia during summer, leading to stronger lower tropospheric moisture convergence and ascending motion, which favor an increase in precipitation. The wetting trend and the associated atmospheric features are successfully reproduced by an atmospheric model driven by the observed Arctic sea ice concentrations and SSTs, whereas the model driven solely by the Arctic sea ice concentrations simulates a negligible increase in precipitation. This is primarily due to the absence of the stronger southerly winds that transport moisture from the Pacific Ocean. The modeling evidence suggests that SST changes in recent decades have a stronger influence on the intensified precipitation than does sea ice. An atmospheric bridge mechanism links the strengthened southerly winds to an upper-level Rossby wave train originating from the North Atlantic. Another atmospheric simulation forced only by Atlantic SST warming recreates the observed enhanced wetting trend in northeastern Siberia and supports the hypothesized atmospheric bridge mechanism.

Research areas: Cryospheric Indicators, Atmospheric/Ocean Indicators
Representing Cloud Water Content of Extensive Cloud Systems Over Land (2018)

We proposed a method to estimate cloud water content (CWC) over land using satellite-based passive microwave brightness temperatures (TBs) at multiple-kilometer resolutions with land and atmosphere assimilation to overcome the challenges associated with estimating the CWC of broad cloud systems over land. This method enables estimation of broad cloud systems over land using multifrequency TBs, which have different sensitivities to land and cloud, by concurrently optimizing land emissions and CWC estimates from models. Estimated CWC was validated using vertical two-dimensional CloudSat products (2B-CWC-RVOD and 2C-ICE). The results were in good accordance with 2B-CWC-RVOD in terms of cloud water path and the vertical distribution of CWC but represented underestimates in comparison to 2C-ICE. We performed sensitivity analysis of CWC estimates of TBs and cloud top height. The results suggested that the error in TBs is not large uncertainty, and that cloud top height affects the estimated CWC more sensitively than TBs. The addition of cloud top height information, as determined from CloudSat products as a constraint of optimization, allows further improvement of the vertical distributions of CWC in case studies. Sensitivity analysis indicated that it is effective to utilize cloud top height data from other satellites, such as next-generation geostationary meteorological satellites, within an error of about ±600 m for further development of our method. This study revealed that the proposed method has great potential to provide unprecedented data for cloud water path and CWC that are continuously distributed over land and ocean with adequate accuracy.

Research areas: Validation
Changing population dynamics and uneven temperature emergence combine to exacerbate regional exposure to heat extremes under 1.5 C and 2 C of warming (2018)

Understanding how continuing increases in global mean temperature will exacerbate societal exposure to extreme weather events is a question of profound importance. However, determining population exposure to the impacts of heat extremes at 1.5 °C and 2 °C of global mean warming requires not only (1) a robust understanding of the physical climate system response, but also consideration of (2) projected changes to overall population size, as well as (3) changes to where people will live in the future. This analysis introduces a new framework, adapted from studies of probabilistic event attribution, to disentangle the relative importance of regional climate emergence and changing population dynamics in the exposure to future heat extremes across multiple densely populated regions in Southern Asia and Eastern Africa (SAEA). Our results reveal that, when population is kept at 2015 levels, exposure to heat considered severe in the present decade across SAEA will increase by a factor of 4.1 (2.4-9.6) and 15.8 (5.0-135) under a 1.5°- and 2.0°-warmer world, respectively. Furthermore, projected population changes by the end of the century under an SSP1 and SSP2 scenario can further exacerbate these changes by a factor of 1.2 (1.0-1.3) and 1.5 (1.3-1.7), respectively. However, a large fraction of this additional risk increase is not related to absolute increases in population, but instead attributed to changes in which regions exhibit continued population growth into the future. Further, this added impact of population redistribution will be twice as significant after 2.0 °C of warming, relative to stabilisation at 1.5 °C, due to the non-linearity of increases in heat exposure. Irrespective of the population scenario considered, continued African population expansion will place more people in locations where emergent changes to future heat extremes are exceptionally severe.

Research areas: Heat
Estimating Southern Ocean Storm Positions With Seismic Observations (2020)

Surface winds from Southern Ocean cyclones generate large waves that travel over long distances (&gt;1,000 km). Wave generation regions are often colocated with enhanced air-sea fluxes and upper ocean mixing. Ocean wave spectra contain information about storm wind speed, fetch size, and intensity at their generation site. Two years of seismic observations on the Ross Ice shelf, combined with modern optimization (machine learning) techniques, are used to trace the origins of wave events in the Southern Ocean with an accuracy of ±110 km and ±2 hr from a hypothetical point source. The observed spectral energy attenuated within sea ice and in the ice shelf but retains characteristics that can be compared to parametric wave models. Comparison with the Modern-Era Retrospective Analysis for Research and Applications, Version 2, and ERA5 reanalyses suggests that less than 45% of ocean swell events can be associated with individual Southern Ocean storms, while the majority of the observed wave events cannot be matched with Southern Ocean high wind events. Reanalysis cyclones and winds are often displaced by about 350 km or 10 hr in Modern-Era Retrospective Analysis for Research and Applications, Version 2, and ERA5 compared to the most likely positions inferred from the seismic spectra. This high fraction of displaced storms in reanalysis products over the South Pacific can be explained by the limited availability of remote sensing observations, primarily caused by the presence of sea ice. Deviation of wave rays from their great circle path by wave-current interaction plays a minor role.

Research areas: Severe Storms
Paradise Islands? Island States and Environmental Performance (2016)

Island states have been shown to outperform continental states on a number of large-scale coordination-related outcomes, such as levels of democracy and institutional quality. The argument developed and tested in this article contends that the same kind of logic may apply to islands environmental performance, too. However, the empirical analysis shows mixed results. Among the 105 environmental outcomes that we analyzed, being an island only has a positive impact on 20 of them. For example, island states tend to outcompete continental states with respect to several indicators related to water quality but not in aspects related to biodiversity, protected areas, or environmental regulations. In addition, the causal factors previously suggested to make islands outperform continental states in terms of coordination have weak explanatory power in predicting islands environmental performance. We conclude the paper by discussing how these interesting findings can be further explored.

Research areas: Habitat Conversion/Fragmentation
Late Quaternary hydroclimate of the Levant: The leaf wax record from the Dead Sea (2022)

The eastern Mediterranean is projected to experience increases in drought and extreme rainfall in response to rising greenhouse gas emissions. Paleoclimate records from this region are crucial to further constrain the response of the water cycle to a globally warmer climate. Of these, the Dead Sea lacustrine record, collected by the Dead Sea Deep Drilling Project (DSDDP), provides a detailed history of climate change over the past 200,000 years and documents large-magnitude changes in regional water balance. Here, we analyze leaf wax isotopes (Dwax, 13Cwax) on DSDDP 5017-1 and compare results to other proxies analyzed on the same core. The Dwax record closely resembles the speleothem 18O record from nearby Soreq Cave, suggesting that both record a regionally coherent signature of glacial-interglacial cycles and the interplay between winter season rainfall and large-scale expansion and contraction of the Afro-Asian monsoon system. Principal components analysis of the pollen and core lithology shows that the first-order driver of variability in the Dead Sea paleoclimate record is global temperature, which controls effective moisture by modulating atmospheric evaporative demand. Leaf wax, pollen, and core lithology all suggest radical changes in the annual cycle of precipitation during the peak of the Last Interglacial. We hypothesize that the Dead Sea Basin experienced a dual-rainfall regime during this time, with intensified winter storms and a summer monsoon season. While these changes were driven by the Earth's precessional cycle, model simulations suggest a similar expansion of the African monsoon domain into the Arabian Peninsula under elevated CO2 levels. The Last Interglacial climate of the DSB provides a glimpse of what future climate in the southeastern Mediterranean region could look like.

Research areas: Atmospheric/Ocean Indicators
Comparison between Large-scale Circulation Anomalies Associated with Interannual Variability and Decadal Change of Summer Arctic Sea Ice (2022)

Abstract Arctic sea ice in summer shows both interannual and long-term variations, and atmospheric circulation anomalies are known to play an important role. This study compares the summertime large-scale circulation anomalies associated with Arctic sea ice on interannual and decadal time scales. The results indicate that the circulation anomalies associated with decreased sea ice on an interannual time scale are characterized by a barotropic anticyclonic anomaly in the central Arctic, and the thermodynamic process is important for the circulationsea ice coupling. On one hand, the descending adiabatic warming in low levels associated with the central Arctic anticyclonic anomaly leads to decreased sea ice by enhancing the downwelling longwave radiation. On the other hand, the anticyclonic anomaly also induces more moisture in low levels. The enhanced moisture and temperature (coupled with each other) further favor the reduction of sea ice by emitting more downwelling longwave radiation. By contrast, associated with the decadal sea ice decline, there is an anticyclonic anomaly over Greenland and a cyclonic anomaly over northern Siberia, and the wind-driven sea ice drift dominates the sea ice decline. The transpolar circulation anomalies between the anticyclonic and cyclonic anomalies promote transport of the ice away from the coasts of Siberia toward the North Pole, and drive the ice out of the Arctic Ocean to the North Atlantic. These circulation anomalies also induce sea ice decline through thermodynamic process, but it is not as significant as that on an interannual time scale.

Research areas: Cryospheric Indicators
Temperature emergence at decision-relevant scales (2021)

Abstract
            
              Signal-to-noise (S/N) ratios are a useful method to assess the significance of future climate change relative to past experiences. Most assessments of climate change emergence have focused on S/N ratios of annual mean temperatures. However, averaging the daily experiences of weather across space or time removes the climate variability actually felt by individuals, and thus presents a less informative view of the speed of current climate change. For example, S/N ratios of annual-mean temperatures experienced by the global population after only 1 C of warming are larger than emergent changes in daily temperatures after 3 C of warming, and generally four times more significant when comparing the same warming threshold. Here, I examine the emergence of S/N ratios in temperature at decision-relevant scales, with a focus on daily temperatures where people live. I find that 2 C of global warming will lead to between 30% and >90% of the global population experiencing the emergence of unusual daily temperatures (>1
              
              ), while it is very unlikely (90% confidence) that more than 60% of the global population will also experience the emergence of unfamiliar daily temperatures (>2
              
              ).

Research areas: Atmospheric/Ocean Indicators
The impact of climate change on incomes and convergence in Africa (2020)

Climate change is projected to detrimentally affect African countries economic development, while income inequalities across economies is among the highest on the planet. However, it is projected that income levels would converge on the continent. Hitherto there is limited evidence on how climate change could affect projected income convergence, accelerating, slowing down, or even reversing this process. Here, we analyze convergence considering climate-change damages, by employing an economic model embedding the three dimensions of risks at the country-level: exposure, vulnerability and hazards. The results show (1) with historical mean climate-induced losses between 10 and 15 percent of GDP per capita growth, the majority of African economies are poorly adapted to their current climatic conditions, (2) Western and Eastern African countries are projected to be the most affected countries on the continent and (3) As a consequence of these heightened impacts on a number of countries, inequalities between countries are projected to widen in the high warming scenario compared to inequalities in the low and without warming scenarios. To mitigate the impacts of economic development and inequalities across countries, we stress (1) the importance of mitigation ambition and Africas leadership in keeping global mean temperature increase below 1.5 C, (2) the need to address the current adaptation deficit as soon as possible, (3) the necessity to integrate quantitatively climate risks in economic and development planning and finally (4) we advocate for the generalization of a special treatment for the most vulnerable countries to access climate-related finance. The analysis raises issues on the ability of African countries to reach their SDGs targets and the potential increasing risk of instability, migration across African countries, of decreased trade and economic cooperation opportunities as a consequence of climate change  exacerbating its negative consequences.

Research areas: Habitat Conversion/Fragmentation
TerrainEnhanced Precipitation Processes Above the Melting Layer: Results From OLYMPEX (2018)

Enhancement of precipitation processes aloft over complex terrain is documented using reflectivity data from an S-band scanning radar (NPOL) that was deployed on the west coast of Washington State during the Olympic Mountains Experiment (OLYMPEX). From November 2015 through mid-January 2016, NPOL obtained high-resolution data within sectors over the ocean and over the windward slopes of the Olympic Mountains. Contoured Frequency by Altitude Diagrams of radar reflectivity highlight a higher frequency of occurrence of larger reflectivities for all heights between 2 and 8 km over land compared to ocean, with the largest difference in the 4- to 6-km range indicating a robust signature of enhancement aloft over the windward slopes. This enhancement pattern is found to some degree under all environmental conditions considered but is especially pronounced during periods of high vapor transport, high melting level height, southwest low-level winds, and neutral stability. These conditions are generally associated with warm sectors of midlatitude cyclones and atmospheric rivers. Past studies have postulated that a secondary enhancement in reflectivity aloft was an intrinsic part of atmospheric river type systems. However, these results show that further significant enhancement of this signature occurs as deep moist-neutral, high water vapor content flow is lifted when it encounters a mountain range. Reflectivity data from the dual-precipitation radar aboard the Global Precipitation Measurement satellite also documents this reflectivity increase aloft over the Olympic Mountains compared to the adjacent ocean, showing the potential for Global Precipitation Measurement to provide reliable estimates of precipitation structure over remote mountainous regions.

Research areas: Atmospheric/Ocean Indicators
Model intercomparison of COSMO 5.0 and IFS 45r1 at kilometer-scale grid spacing (2021)

Abstract. The increase in computing power and recent model developments allow for the use of global kilometer-scale weather and climate models for routine forecasts. At these scales, deep convective processes can be partially resolved explicitly by the model dynamics. Next to horizontal resolution, other aspects such as the applied numerical methods, the use of the hydrostatic approximation, and time step size are factors that might influence a model's ability to resolve deep convective processes. In order to improve our understanding of the role of these factors, a model intercomparison between the nonhydrostatic COSMO model and the hydrostatic Integrated Forecast System (IFS) from ECMWF has been conducted. Both models have been run with different spatial and temporal resolutions in order to simulate 2 summer days over Europe with strong convection. The results are analyzed with a focus on vertical wind speed and precipitation. Results show that even at around 3 km horizontal grid spacing the effect of the hydrostatic approximation seems to be negligible. However, time step proves to be an important factor for deep convective processes, with a reduced time step generally allowing for higher updraft velocities and thus more energy in vertical velocity spectra, in particular for shorter wavelengths. A shorter time step is also causing an earlier onset and peak of the diurnal cycle. Furthermore, the amount of horizontal diffusion plays a crucial role for deep convection with more diffusion generally leading to larger convective cells and higher precipitation intensities. The study also shows that for both models the parameterization of deep convection leads to lower updraft and precipitation intensities and biases in the diurnal cycle with a precipitation peak which is too early.

Research areas: Validation
Stratospheric and Tropospheric Flux Contributions to the Polar Cap Energy Budgets (2021)

Abstract The flux of moist static energy into the polar regions plays a key role in the energy budget and climate of the polar regions. While usually studied from a vertically integrated perspective (Fwall), this analysis examines its vertical structure, using the NASA-MERRA-2 reanalysis to compute climatological and anomalous fluxes of sensible, latent, and potential energy across 70N and 65S for the period 19802016. The vertical structure of the climatological flux is bimodal, with peaks in the middle to lower troposphere and middle to upper stratosphere. The near-zero flux at the tropopause defines the boundary between stratospheric (Fstrat) and tropospheric (Ftrop) contributions to Fwall. Especially at 70N, Fstrat is found to be important to the climatology and variability of Fwall, contributing 20.9 W m2 to Fwall (19% of Fwall) during the winter and explaining 23% of the variance of Fwall. During winter, an anomalous poleward increase in Fstrat preceding a sudden stratospheric warming is followed by an increase in outgoing longwave radiation anomalies, with little influence on the surface energy budget of the Arctic. Conversely, a majority of the energy input by an anomalous poleward increase in Ftrop goes toward warming the Arctic surface. Overall, Ftrop is found to be a better metric than Fwall for evaluating the influence of atmospheric circulations on the Arctic surface climate.

Research areas: Atmospheric/Ocean Indicators