rlacombe/ClimateX huggingface dataset:
Combining the lines of evidence and adding uncertainties in quadrature, the ERFari+aci estimated for 2014 relative to 1750 is assessed to be –1.3 [–2.0 to –0.6] W m–2 (IPCC AR6_WGI, confidence: medium)
However, based on a general reduction in global mean AOD over this period (Section 2.2.6 and Figure 2.9), combined with a reduction in emissions of aerosols and their precursors in updated emissions inventories (Hoesly et al., 2018), the aerosol ERF is assessed to have decreased in magnitude from about 2014 to 2019 (IPCC AR6_WGI, confidence: medium)
Aerosols are therefore assessed to have contributed an ERF of –1.1 [–1.7 to –0.4] W m–2 over 1750–2019 (IPCC AR6_WGI, confidence: medium)
Adding the irrigation effect to this gives an overall assessment of the ERF from land-use change of –0.20 ± 0.10 W m–2 (IPCC AR6_WGI, confidence: medium)
The best estimate solar ERF is assessed to be 0.01 W m–2, using the 14C reconstruction from SATIRE-M, with a likely range of –0.06 to +0.08 W m–2 (IPCC AR6_WGI, confidence: medium)
The Lockwood and Ball (2020) full uncertainty range is halved as the period of reduced solar activity in the Maunder Minimum had ended by 1750 (IPCC AR6_WGI, confidence: medium)
The ERF for volcanic stratospheric aerosols is assessed to be –20 ± 5 W m–2 per unit SAOD (IPCC AR6_WGI, confidence: medium)
The stratospheric-temperature-adjusted radiative efficiency for CH 4 is increased by approximately 25% (IPCC AR6_WGI, confidence: high)
The tropospheric adjustment is tentatively assessed to be –14% (IPCC AR6_WGI, confidence: low)
A +7% tropospheric adjustment has been added to the radiative efficiency for N 2O and +12% to CFC-11 and CFC-12 (IPCC AR6_WGI, confidence: low)
However, the total aerosol ERF is assessed to be more negative compared to AR5, due to revised estimates rather than trends (IPCC AR6_WGI, confidence: high)
Carbon dioxide continues to contribute the largest part (56 ± 16%) of this GHG ERF (IPCC AR6_WGI, confidence: high)
As discussed in Section 7.3.3, aerosols have in total contributed an ERF of –1.1 [–1.7 to –0.4] W m–2 over 1750–2019 (IPCC AR6_WGI, confidence: medium)
The total human forced GSAT change from 1750 to 2019 is calculated to be 1.29 [1.00 to 1.65] °C (IPCC AR6_WGI, confidence: high)
Nonetheless, simple physically basedof a WMGHG warming of 1.58 [1.17 to 2.17] °C (high confidence), a warming from ozone changes of 0.23 [0.11 to 0.39] °C (high confidence), and a cooling of –0.50 [–0.22 to –0.96] °C from aerosol effects (IPCC AR6_WGI, confidence: medium)
There is also a –0.06 [–0.15 to +0.01] °C contribution from surface reflectance changes which is dominated by land-use change (IPCC AR6_WGI, confidence: medium)
However, since 1980 the aerosol cooling trend has stabilized and may have started to reverse, so that over the last few decades the long-term warming has been occurring at a faster rate than would be expected due to CO 2 alone (IPCC AR6_WGI, confidence: high)
Since AR5, several studies have confirmed that a shift from tundra to boreal forests and the associated albedo change leads to increased warming in Northern Hemisphere high latitudes (IPCC AR6_WGI, confidence: high)
Given the limited number of studies, we take the full range of estimates discussed above for the biogeophysical feedback parameter, and assess the very likely range to be from 0.0 to +0.3 W m–2 °C–1, with a central estimate of +0.15 W m–2 °C–1 (IPCC AR6_WGI, confidence: low)
As such, overall, on multi- centennial time scales the feedback parameter associated with ice sheets is likely negative (medium confidence), but on multi-millennial time scales by the time the ice sheets reach equilibrium, the feedback parameter is very likely positive (IPCC AR6_WGI, confidence: high)
For both the MPWP and EECO, models are more consistent with the temperature and CO 2 proxies than at the time of AR5 (IPCC AR6_WGI, confidence: high)
For the LGM Northern Hemisphere, which is the region with the most data and the time period with the least uncertainty in model boundary conditions, polar amplification in the PMIP4 ensemble mean is in good agreement with the proxies, especially for SAT (IPCC AR6_WGI, confidence: medium)
It is very likely that the warming in the Arctic will be more pronounced than the global average over the 21st century (IPCC AR6_WGI, confidence: high)
This is supported by models’ improved ability to simulate polar amplification during past time periods, compared with at the time of AR5 (IPCC AR6_WGI, confidence: high)
The value of α’ is larger if quantified based on the observed pattern of warming since 1980 (Figure 2.11b) which is more distinct from the equilibrium warming pattern expected under CO 2 forcing (IPCC AR6_WGI, confidence: high)
In summary, the process-based estimate of TCR is assessed to have the central value of 2.0°C with the likely range from 1.6 to 2.7 °C and the very likely range from 1.3 to 3.1 °C (IPCC AR6_WGI, confidence: high)
Regression-based feedbacks thus provide estimates of the radiative feedbacks that are associated with internal climate variability (e.g., Brown et al., 2014), and do not provide a direct estimate of ECS (IPCC AR6_WGI, confidence: high)
Estimates based on the response to volcanic eruptions agree with other lines of evidence (Knutti et al., 2017), but they do not constitute a direct estimate of ECS (IPCC AR6_WGI, confidence: high)
However, there is robust evidence and high agreement across the lines of evidence that ECS is extremely likely greater than 1.6°C (IPCC AR6_WGI, confidence: high)
There is robust evidence and medium agreement across the lines of evidence that ECS is very likely greater than 1.8°C and likely greater than 2.2°C (IPCC AR6_WGI, confidence: high)
These ranges of ECS correspond to estimates based on historical global energy budget constraints (Section 7.5.2.1) under the assumption of no feedback dependence on evolving SST patterns (i.e., α’ = 0) and thus represent an underestimate of the true ECS ranges that can be inferred from this line of evidence (IPCC AR6_WGI, confidence: high)
Global energy budget constraints indicate a central estimate (median) TCR value of 1.9°C and that TCR is likely in the range 1.5 to 2.3 °C and very likely in the range 1.3 to 2.7 °C (IPCC AR6_WGI, confidence: high)
As such, based solely on the paleoclimate record, it is assessed to be very likely that ECS is greater than 1.5°C (IPCC AR6_WGI, confidence: high)
Despite the large variation in individual studies at the extreme upper end, all except two studies (both of which are from glacial–interglacial time periods associated with low confidence) have central estimates that are below 6°C; overall we assess that it is extremely likely that ECS is below 8°C (IPCC AR6_WGI, confidence: high)
The high ECS and TCR values can in some CMIP6 models be traced to improved representation of extratropical cloud feedbacks (IPCC AR6_WGI, confidence: medium)
Solely based on its ECS or TCR values an individual ESM cannot be ruled out as implausible, though some models with high (greater than 5°C) and low (less than 2°C) ECS are less consistent with past climate change (IPCC AR6_WGI, confidence: high)
Global ocean heat uptake is a smaller source of uncertainty in long-term surface warming (IPCC AR6_WGI, confidence: high)
In summary, GWPs and GTPs for methane and nitrous oxide are slightly lower than in AR5 (IPCC AR6_WGI, confidence: medium)
Estimates of the yield are 61% (Boucher et al., 2009) and 88% (Shindell et al., 2017), so the assessed range is 50–100% with a central value of 75% (IPCC AR6_WGI, confidence: low)
Methane from fossil fuel sources has therefore slightly higher emissions metric values than those from biogenic sources (IPCC AR6_WGI, confidence: high)
Hence, net zero CO 2 and net zero GHG, quantified using these new approaches, would both lead to approximately stable contributions to temperature change after net zero emissions are achieved (IPCC AR6_WGI, confidence: high)
The overall effect of anthropogenic aerosols is to reduce global precipitation and alter large-scale atmospheric circulation patterns through their well- understood surface radiative cooling effect (IPCC AR6_WGI, confidence: high)
Land- use and land-cover changes also drive regional water cycle changes through their influence on surface water and energy budgets (IPCC AR6_WGI, confidence: high)
An increase in near-surface atmospheric water holding capacity of about 7% per 1°C of warming explains a similar magnitude of intensification of heavy precipitation events (from sub-daily up to seasonal time scales) that increases the severity of flood hazards when these extremes occur (IPCC AR6_WGI, confidence: high)
The severity of very wet and very dry events increases in a warming climate (IPCC AR6_WGI, confidence: high)
A slowdown of tropical circulation with global warming partly offsets the warming- induced strengthening of precipitation in monsoon regions (IPCC AR6_WGI, confidence: high)
Greater warming over land than over the ocean alters atmospheric circulation patterns and, on average, reduces continental near-surface relative humidity, which contributes to regional drying (IPCC AR6_WGI, confidence: high)
Global warming has contributed to an overall increase in atmospheric moisture and precipitation intensity (high confidence), increased terrestrial evapotranspiration (medium confidence), influenced global patterns in aridity (very likely), and enhanced contrasts in surface salinity and precipitation minus evaporation patterns over the oceans (IPCC AR6_WGI, confidence: high)
Earlier onset of spring snowmelt and increased melting of glaciers have already contributed to seasonal changes in streamflow in high-latitude and low-elevation mountain catchments (IPCC AR6_WGI, confidence: high)
Shifts in the tropical rain belt are associated with the inter-hemispheric temperature response to the time-evolving radiative influence of anthropogenic aerosols and the ongoing warming influence of greenhouse gases (IPCC AR6_WGI, confidence: high)
Cooling in the Northern Hemisphere by sulphate aerosols explained a southward shift in the tropical rain belt and contributed to the Sahel drought from the 1970s to the 1980s (high confidence), subsequent recovery from which has been linked with greenhouse gas warming (IPCC AR6_WGI, confidence: medium)
Observed changes in regional monsoon precipitation, especially over South Asia, East Asia and West Africa, have been limited over much of the 20th century due to increases driven by warming from greenhouse gases being counteracted by decreases due to cooling from anthropogenic aerosols (IPCC AR6_WGI, confidence: high)
Urbanization has increased local precipitation (medium confidence) and resulting runoff intensity (IPCC AR6_WGI, confidence: high)
Projected increases in precipitation amount and intensity will be associated with increased runoff in the northern high latitudes (IPCC AR6_WGI, confidence: high)
Runoff from small glaciers will typically decrease through loss of ice mass, while runoff from large glaciers is likely to increase with increasing global warming until glacier mass becomes depleted (IPCC AR6_WGI, confidence: high)
In the Mediterranean, south-western South America, and western North America, future aridification will far exceed the magnitude of change seen in the last millennium (IPCC AR6_WGI, confidence: high)
Some tropical regions are also projected to experience increased aridity, including the Amazon basin and Central America (IPCC AR6_WGI, confidence: high)
In the tropics and in the extratropics of both hemispheres during summer/warm season, interannual variability of precipitation and runoff over land is projected to increase at a faster rate than changes in seasonal mean precipitation amount (IPCC AR6_WGI, confidence: medium)
Precipitation extremes will increase in almost all regions (high confidence), even where seasonal mean precipitation is projected to decrease (IPCC AR6_WGI, confidence: medium)
Summer monsoon precipitation is projected to increase for the South, South East and East Asian monsoon domains, while North American monsoon precipitation is projected to decrease (IPCC AR6_WGI, confidence: medium)
West African monsoon precipitation is projected to increase over the Central Sahel and decrease over the far western Sahel (IPCC AR6_WGI, confidence: medium)
A continued poleward shift of storm tracks in the Southern Hemisphere (likely) and the North Pacific (IPCC AR6_WGI, confidence: medium)
The annual contrast between the wettest and driest month of the year is likely to increase by 3–5% per 1°C in most monsoon regions in terms of precipitation, precipitation minus evaporation, and runoff (IPCC AR6_WGI, confidence: medium)
High-resolution climate and hydrological models provide a better representation of land surfaces, including topography, vegetation and land-use change, which improve the accuracy of simulations of regional changes in the water cycle (IPCC AR6_WGI, confidence: high)
Water cycle changes that have already emerged from natural variability will become more pronounced in the near term, but the occurrence of volcanic eruptions (either single large events or clustered smaller ones) can alter the water cycle for several years, decreasing global mean land precipitation and altering monsoon circulation (IPCC AR6_WGI, confidence: high)
Non-linear water cycle responses are explained by the interaction of multiple drivers, feedbacks and time scales (IPCC AR6_WGI, confidence: high)
Non-linear responses of regional runoff, groundwater recharge and water scarcity highlight the limitations of simple pattern-scaling techniques (IPCC AR6_WGI, confidence: medium)
Water resources fed by melting glaciers are particularly exposed to non-linear responses (IPCC AR6_WGI, confidence: high)
The paleoclimate records show that a collapse in the Atlantic Meridional Overturning Circulation (AMOC) causes abrupt shifts in the water cycle (IPCC AR6_WGI, confidence: high)
The impact of SRM can affect different regions in potentially disruptive ways (IPCC AR6_WGI, confidence: low)
Detectable human influ ence on changes to the water cycle were found in atmospheric moisture content (medium confidence), global-scale changes of precipitation over land (medium confidence), intensification of heavy precipitation events over land regions where sufficient data networks exist (IPCC AR6_WGI, confidence: medium)
Further evidence that anthropogenic global warming has caused an increase in the frequency, intensity and/or amount of heavy precipitation events at the global scale (medium confidence), as well as in drought occurrence in the Mediterranean region (IPCC AR6_WGI, confidence: medium)
A key finding is that ‘limiting global warming to 1.5°C compared to 2°C would approximately halve the proportion of the world population expected to suffer water scarcity, although there is considerable variability between regions (IPCC AR6_WGI, confidence: medium)
This Report indicates that since 1850–1900, land surface temperature has risen nearly twice as much as global surface temperature (high confidence), with an increase in dry climates (IPCC AR6_WGI, confidence: high)
Land surface processes modulate the likelihood, intensity and duration of many extreme events including droughts (medium confidence) and heavy precipitation (IPCC AR6_WGI, confidence: medium)
The direction and magnitude of hydrological changes induced by land use change and land surface feedbacks vary with location and season (IPCC AR6_WGI, confidence: high)
Desertification exacerbates climate change through feedbacks involving vegetation cover, greenhouse gases and mineral dust aerosol (IPCC AR6_WGI, confidence: high)
Urbanization increases extreme rainfall events over or downwind of cities (IPCC AR6_WGI, confidence: medium)
Global precipitation increases due to GHGs are offset by the well-understood overall surface radiative cooling effect by aerosols (IPCC AR6_WGI, confidence: high)
Over land, the average warming-related increase in precipitation is expected to be smaller than over the ocean due to increasing land –ocean thermal contrast and surface feedbacks, but the overall precipitation increase over land is generally reinforced by fast atmospheric responses to GHGs that strengthens convergence of winds (IPCC AR6_WGI, confidence: medium)
Global mean precipitation and evaporation increase at a lower rate than atmospheric moisture per 1°C of global warming (IPCC AR6_WGI, confidence: high)
To summarize, increased moisture transport from evaporative oceans to high precipitation regions of the atmospheric circulation will drive amplified P–E and salinity patterns over the ocean (IPCC AR6_WGI, confidence: high)
Greater warming over land than ocean alters atmospheric circulation patterns and on average reduces continental near-surface relative humidity which along with vegetation feedbacks can contribute to regional decreases in precipitation (IPCC AR6_WGI, confidence: high)
Mean tropical circulation is expected to slow with global warming (high confidence) but temporary multi-decadal strengthening is possible due to internal variability (IPCC AR6_WGI, confidence: medium)
Slowing of the tropical circulation reduces the meridional P–E gradient over the Pacific and can partly offset thermodynamic amplification of P–E patterns and strengthening of monsoons (IPCC AR6_WGI, confidence: high)
Melting of snowpack or glaciers can increase streamflow in high-latitude and high-altitude catchments until frozen water reserves are depleted (IPCC AR6_WGI, confidence: high)
On a global level, warmer temperatures increase evaporative demand in the atmosphere, and thus (assuming sufficient soil moisture is available) increase moisture loss from evapotranspiration (IPCC AR6_WGI, confidence: high)
In snow-dominated regions, high temperatures increase the fraction of precipitation falling as rain instead of snow and advance the timing of spring snowmelt (IPCC AR6_WGI, confidence: high)
While potentially buffering water resource capacity, in some cases these interventions may unexpectedly increase vulnerability (IPCC AR6_WGI, confidence: medium)
Beyond a lack of precipitation, changes in evapotranspiration are critical components of drought, because these can lead to soil moisture declines (IPCC AR6_WGI, confidence: high)
Under very dry soil conditions, evapotranspiration becomes restricted and plants experience water stress in response to increased atmospheric demand (IPCC AR6_WGI, confidence: medium)
Human activities and decision-making have a critical impact on drought severity (IPCC AR6_WGI, confidence: high)
Urbanization can increase local precipitation (medium confidence) and resulting runoff intensity (IPCC AR6_WGI, confidence: high)
A warming climate combined with direct human demand for water is expected to deplete groundwater resources in dry regions (IPCC AR6_WGI, confidence: high)
In particular, aerosols induce intense convection at the Himalaya foothills during the pre-monsoon season, which generates a regional convergence there (IPCC AR6_WGI, confidence: medium)
It is likely that the global land P–E variations observed since the late 1970s were dominated by internal variability, mostly linked to ENSO teleconnections (IPCC AR6_WGI, confidence: medium)
There is further evidence of a faster increase since the 1980s (IPCC AR6_WGI, confidence: medium)
There is, however, a detectable increase in northern high-latitude annual precipitation over land which has been primarily driven by human-induced global warming (IPCC AR6_WGI, confidence: high)
Human influence has strengthened the zonal mean precipitation contrast between the wet tropics and dry subtropics since the 1980s (IPCC AR6_WGI, confidence: medium)
In contrast to AR5, there are now consistent trends in pan evaporation and evapotranspiration at the global scale, given the recent increase in both variables since the mid-1990s (IPCC AR6_WGI, confidence: medium)
Plant water use efficiency (WUE) is expected to rise with CO 2 levels (IPCC AR6_WGI, confidence: high)
Both central and north-eastern Africa have experienced a decline in rainfall since about 1980 (IPCC AR6_WGI, confidence: high)
In some regions of western North America and the Mediterranean, paleoclimate evidence suggests that recent warming has resulted in droughts that are of similar or greater intensity than those reconstructed over the last millennium (IPCC AR6_WGI, confidence: medium)
In summary, human-induced global warming has been the primary driver of a global glacier recession since the early 20th century (IPCC AR6_WGI, confidence: high)
Most glaciers have lost mass more rapidly since the 1960s and in an unprecedented way over the last decade, thereby contributing to increased glacier runoff, especially from larger glaciers until a maximum is reached, which tends to occur later in basins with larger glaciers and higher ice-cover fractions (IPCC AR6_WGI, confidence: high)
AR6 assesses that NH spring snow cover has been decreasing since 1978 (very high confidence) and that this trend extends back to 1950 (IPCC AR6_WGI, confidence: high)
In summary, a decline in the spring NH snow cover extent, snow depth and duration has been observed since the late 1960s and has been attributed to human influence (IPCC AR6_WGI, confidence: high)
Decreasing precipitation trends in the NH during the 1950s –1980s have been attributed to anthropogenic aerosol emissions from North America and Europe (IPCC AR6_WGI, confidence: high)
In AR6, Chapter 2 (Section 2.3.1.4.1) states that the HC has very likely widened and strengthened since at least the 1980s, mostly in the NH (IPCC AR6_WGI, confidence: medium)
As assessed in Section 3.3.3.1, GHG increases and stratospheric ozone depletion have contributed to the expansion of the zonal mean HC in the SH since around 1980, and the expansion of the NH HC has not exceeded the range of internal variability (IPCC AR6_WGI, confidence: medium)
GHG increases and stratospheric ozone depletion have contributed to expansion of the zonal mean HC in the SH since around 1970, while the expansion of the NH HC has not exceeded the range of internal variability (IPCC AR6_WGI, confidence: medium)
The causes of the observed strengthening of the WC during 1980 –2014 are not well understood due to competing influences from individual external forcings and since this strengthening is outside the range of variability simulated in coupled models (IPCC AR6_WGI, confidence: medium)
The SAsiaM strengthened during past periods of enhanced summer insolation in the NH, such as the early-to-mid Holocene warm period around 9000 to 6000 years before the present (BP) (Masson-Delmotte et al., 2013; Mohtadi et al., 2016; Braconnot et al., 2019) and weakened during cold periods (IPCC AR6_WGI, confidence: high)
Results from climate models indicate that anthropogenic aerosol forcing has dominated the recent decrease in summer monsoon precipitation, as opposed to the expected intensification due to GHG forcing (IPCC AR6_WGI, confidence: high)
On paleoclimate time scales, the SAsiaM strengthened in response to enhanced summer warming in the NH during the early-to-mid Holocene, while it weakened during cold intervals (IPCC AR6_WGI, confidence: high)
These changes are tightly linked to orbital forcing and changes in high-latitude climate (IPCC AR6_WGI, confidence: medium)
The transition towards a positive PDV phase has been one of the main drivers of the EAsiaM weakening since the 1970s (IPCC AR6_WGI, confidence: high)
On paleoclimate time scales, enhanced summer insolation in the Northern Hemisphere (NH) intensified the WAfriM precipitation during the early-to-mid Holocene (IPCC AR6_WGI, confidence: high)
The WAfriM experienced the wettest decade of the 20th century during the 1950s and early 1960s (IPCC AR6_WGI, confidence: high)
Wetter conditions of the WAfriM prevailed later from the mid-to-late 1990s, although the positive trend in precipitation started since the late 1980s (see also Section 10.4.2.1) over the Sahel (high confidence) and in the Guinean coastal region (IPCC AR6_WGI, confidence: medium)
In summary, most regions of West Africa experienced a wet period in the mid-20th century followed by a very dry period in the 1970s and 1980s that is attributed to aerosol cooling of the NH (IPCC AR6_WGI, confidence: high)