rlacombe/ClimateX huggingface dataset:
These differences due to experimental configuration would be smaller still under scenarios with lower CO 2 levels, and so we assess that results from concentration-driven and emissions- driven configurations do not affect the assessment of GSAT projections (IPCC AR6_WGI, confidence: high)
Based on these results, we conclude that global land precipitation is larger during the period 2081–2100 than during the period 1995–2014, under all scenarios considered here (IPCC AR6_WGI, confidence: high)
There is no change in subtropical precipitation in the North Atlantic following SSP1-1.9, SSP1-2.6, or SSP2-4.5 (IPCC AR6_WGI, confidence: high)
These range from 43% under RCP2.6 and 94% under RCP8.5 in September, and from 8% under RCP2.6 and 34% under RCP8.5 in March (IPCC AR6_WGI, confidence: medium)
Based on results from the CMIP6 models, we conclude that on average the Arctic will become practically ice-free in September by the end of the 21st century under SSP2-4.5, SSP3-7.0, and SSP5-8.5 (IPCC AR6_WGI, confidence: high)
Also, in the CMIP6 models, Arctic SIA in March decreases in the future, but to a much lesser degree, in percentage terms, than in September (IPCC AR6_WGI, confidence: high)
The individual model simulations, for which there are twenty for each stabilized temperature level, show that the probability of the Arctic becoming practically ice free at the end of the 21st century is significantly higher for 2°C warming than for 1.5°C warming above 1850–1900 levels (IPCC AR6_WGI, confidence: high)
Further, AR5 concluded that for the period 2081–2100, compared to 1986–2005, GMSL rise is likely (IPCC AR6_WGI, confidence: medium)
In summary, we assess from the CMIP6 models that AMOC weakening over the 21st century is very likely ; the rate of weakening is approximately independent of the emissions scenario (IPCC AR6_WGI, confidence: high)
In summary, in these model simulations the AMOC recovers over several centuries after the cessation of CO 2 emissions (IPCC AR6_WGI, confidence: medium)
We assess that the cumulative uptake of carbon by the ocean and by land will increase through the 21st century irrespective of the considered emissions scenarios except SSP1-1.9 (IPCC AR6_WGI, confidence: very high)
Based on results from the CMIP6 models we conclude that, except for the lower-emissions scenarios SSP1-1.9 and SSP1-2.6, ocean surface pH decreases monotonically through the 21st century (IPCC AR6_WGI, confidence: high)
Strong positive trends for the NAM/NAO indices were observed since 1960, which have weakened since the 1990s (IPCC AR6_WGI, confidence: high)
Based on CMIP6 model results displayed in Figure 4.9a, we conclude that the boreal wintertime surface NAM is more positive by the end of the 21st century under SSP3-7.0 and SSP5-8.5 (IPCC AR6_WGI, confidence: high)
On the other hand, under neither of the lowest emissions scenarios, SSP1-1.9 and SSP1-2.6, does the NAM show a robust change, by the end of the 21st century (IPCC AR6_WGI, confidence: high)
Over the instrumental period, there has been a robust positive trend in the SAM index, particularly since 1970 (IPCC AR6_WGI, confidence: high)
In summary, under the highest emissions scenarios in the CMIP6 models, the SAM in the austral summer becomes more positive through the 21st century (IPCC AR6_WGI, confidence: high)
Over the mid-term period 2041–2060, the very likely GSAT ranges of SSP1-1.9 and SSP5-8.5 are almost completely distinct (IPCC AR6_WGI, confidence: high)
CMIP6 models project a wider range of GSAT change than the assessed range (IPCC AR6_WGI, confidence: high)
Roughly half of this difference arises from a larger historical warming diagnosed in AR6, while the other half arises because for central estimates of climate sensitivity, most scenarios show stronger warming over the near term than was estimated as ‘current’ in SR1.5 (IPCC AR6_WGI, confidence: medium)
If ECS and TCR lie near the lower end of the assessed very likely range, crossing the 1.5°C warming threshold is avoided in scenarios SSP1-1.9 and SSP1-2.6 (IPCC AR6_WGI, confidence: medium)
The AR5 further assessed that it is more likely than not that the mean GSAT for the period 2016–2035 will be more than 1°C above the mean for 1850–1900, and it is very unlikely that it will be more than 1.5°C above the 1850–1900 mean (IPCC AR6_WGI, confidence: medium)
Averaged over the twenty years of the near term and across all scenarios, GSAT is very likely to be higher than over 1995–2014 by 0.4°C–1.0°C (Table 4.5), with most of the uncertainty arising from that in ECS and TCR (IPCC AR6_WGI, confidence: high)
For annual mean GSAT, uncertainty in near-term projections arises in roughly equal measure from internal variability and model uncertainty (IPCC AR6_WGI, confidence: high)
Forecasts initialized from recent observations simulate GSAT changes for the period 2019–2028 relative to the recent past that are consistent with the assessed very likely range in annual mean GSAT (IPCC AR6_WGI, confidence: high)
By 2030, GSAT in any individual year could exceed 1.5°C relative to 1850–1900 with a likelihood between 40 and 60 percent, across the scenarios considered here (IPCC AR6_WGI, confidence: medium)
Near-term projected changes in precipitation are uncertain mainly because of natural internal variability, model uncertainty, and uncertainty in natural and anthropogenic aerosol forcing (IPCC AR6_WGI, confidence: medium)
In summary, we assess that near-term changes in global monsoon precipitation and circulation will be affected by the combined effects of model uncertainty and internal variability, such as AMV and PDV, which together are larger than the forced signal (IPCC AR6_WGI, confidence: medium)
Based on results from CMIP6 models, we conclude that SSP2-4.5, SSP3-7.0, and SSP5-8.5 all clearly lead to increasing 10-, 20-, and 30-year trends in ocean carbon flux over the near term (IPCC AR6_WGI, confidence: high)
Considering these new results since AR5, in the near-term it is likely that any anthropogenic forced signal in the NAM will be of comparable magnitude or smaller than natural internal variability in the NAM (IPCC AR6_WGI, confidence: medium)
Hence, no robust change in amplitude of ENSO SST and rainfall variability is expected in the near term although the rainfall variability slightly increases (IPCC AR6_WGI, confidence: medium)
However, some studies show that despite severe model biases there are skilful predictions in the mean state of tropical Atlantic surface temperature several years ahead (IPCC AR6_WGI, confidence: medium)
The AR5 assessed that emission reductions aimed at decreasing local air pollution could have a near-term warming impact on climate (IPCC AR6_WGI, confidence: high)
Volcanic eruptions generally result in decreased global precipitation for up to a few years following the eruption (Iles and Hegerl, 2014, 2015; Man et al., 2014), with climatologically wet regions drying and climatologically dry regions wetting (IPCC AR6_WGI, confidence: medium)
In these simulations with multiple volcanic forcing futures there is: (i) an increase in the frequency of extremely cold individual years; (ii) an increased likelihood of decades with negative GSAT trend (decades with negative GSAT trends become 50% more commonplace); (iii) later anthropogenic signal emergence (the mean time at which the signal of global warming emerges from the noise of natural climate variability is delayed almost everywhere) (IPCC AR6_WGI, confidence: high)
Yet, remaining disagreements reflect differences in the volcanic forcing datasets used in the simulations (IPCC AR6_WGI, confidence: medium)
The ratio of land-to-ocean warming is greater than one for almost all regions (IPCC AR6_WGI, confidence: high)
Projected reduction in the strength of the AMOC over the 21st century is expected to reduce Arctic warming, but even a strong AMOC reduction would not eliminate Arctic amplification entirely (IPCC AR6_WGI, confidence: medium)
There is growing evidence that year-to-year and day-to-day temperature variability decreases in winter over northern mid- to high-latitudes (Fischer et al., 2011; De Vries et al., 2012; Screen, 2014; Schneider et al., 2015; Holmes et al., 2016; Borodina et al., 2017; Tamarin-Brodsky et al., 2020) which implies that the lowest temperatures rise more than the respective climatological mean temperatures (IPCC AR6_WGI, confidence: medium)
Consistent with the AR5, patterns of precipitation change are very likely to increase in the high latitudes especially during local winter and over tropical oceans under SSP3-7.0 (IPCC AR6_WGI, confidence: high)
CMIP6 projections show an increase in precipitation over larger parts of the monsoon regions and decreases in many subtropical regions including the Mediterranean, southern Africa and south-west Australia (IPCC AR6_WGI, confidence: medium)
CMIP6 models show greater increases in precipitation over land than either globally or over the ocean (IPCC AR6_WGI, confidence: high)
The patterns of precipitation change will exhibit substantial regional differences and seasonal contrast as GSAT increases over the 21st century (IPCC AR6_WGI, confidence: high)
The patterns of monsoon rainfall change in the mid- to long-term include a north–south asymmetry characterized by greater increase in the NH than the SH, and an East–West asymmetry characterized by enhanced Asian-African monsoons and weakened North American monsoon (IPCC AR6_WGI, confidence: medium)
Monsoon precipitation responses depend on region and emissions scenario (IPCC AR6_WGI, confidence: high)
The AR5 assessed that a poleward shift of the SH westerlies and storm track is likely by the end of the 21st century under RCP8.5 (IPCC AR6_WGI, confidence: medium)
The projected large-scale surface ocean acidification will be primarily determined by the pathway of atmospheric CO 2, with weak dependence on change in climate (IPCC AR6_WGI, confidence: high)
However, for a given atmospheric CO 2 scenario, uncertainty in projected ocean acidification increases with ocean depth because of model-simulated differences in ocean circulation that transports anthropogenic CO 2 from the surface to bottom ocean (IPCC AR6_WGI, confidence: high)
To conclude, the forced change in ENSO SST variability is highly uncertain in CMIP5 and CMIP6 models (IPCC AR6_WGI, confidence: medium)
In the Southern Hemisphere the strongest warming over land is to occur, at any given level of global warming, over the subtropical areas of South America, southern Africa and Australia (IPCC AR6_WGI, confidence: high)
Across the globe, in the tropics, subtropics, and mid- to high latitudes, temperatures tend to scale linearly with the level of increase in GSAT and patterns of change are largely scenario independent (IPCC AR6_WGI, confidence: high)
The increases and decreases in precipitation will amplify at higher levels of global warming (IPCC AR6_WGI, confidence: high)
Over the austral-winter rainfall regions of south-western South America, South Africa and Australia, projected decreases in mean annual rainfall show high agreement across models and a strong climate change signal even under 1.5°C of global warming, with further amplification of the signal at higher levels of global warming (IPCC AR6_WGI, confidence: high)
As warming increases, a larger global and land area will experience statistically significant increases or decreases in precipitation (IPCC AR6_WGI, confidence: medium)
Although these climate quantities are not fully reversible, the overshoot scenario results in reduced climate change compared with stabilisation or continued increase in greenhouse gases (Tsutsui et al., 2006; Palter et al., 2018; Tachiiri et al., 2019) (IPCC AR6_WGI, confidence: high)
TCRE remains a valuable concept to assess climate policy goals and how to achieve them but given the non-reversibility of different climate metrics with CO 2 and GSAT reductions, it has limitations associated with evaluating the climate response under overshoot scenarios and CO 2 removal (IPCC AR6_WGI, confidence: medium)
Compared with the differences between the CMIP5 and CMIP6 multi-model ensembles for the same scenario pairs (Table A6 in Tebaldi et al., 2021), the higher ERFs of the SSP scenarios contribute approximately half of the warmer CMIP6 SSP outcomes (IPCC AR6_WGI, confidence: medium)
Surface warming would likewise initially continue under scenarios of decreasing emissions, resulting in a substantial lag between a peak in CO 2 emissions and peak warming (IPCC AR6_WGI, confidence: high)
Among global quantities, emergence of the response to differing CO 2 emissions – representing differences between low- and high-emissions scenarios – is first expected to arise in global mean CO 2 concentrations, about 10 years after emissions pathways have started diverging (IPCC AR6_WGI, confidence: high)
This earlier diagnosed time of emergence compared to Marotzke (2019), while using a similar statistical approach, presumably arose because of the longer-period trends (20 rather than 15 years) and the larger difference between emissions trajectories considered (IPCC AR6_WGI, confidence: medium)
During the near term, a small fraction of the surface can show cooling under all scenarios assessed here, so near-term cooling at any given location is fully consistent with globally averaged surface warming (IPCC AR6_WGI, confidence: high)
Hence, the potential role that CDR will play in lowering the temperature in high-emissions scenarios is limited (IPCC AR6_WGI, confidence: medium)
The climate system response to the deployment of CDR is expected to be delayed by years (e.g., in temperature, precipitation, sea ice extent) to centuries (e.g., sea level and AMOC) (IPCC AR6_WGI, confidence: high)
The climate response to a sudden and sustained CDR termination would depend on the amount of CDR-induced cooling prior to termination and the rate of background CO 2 emissions at the time of termination (IPCC AR6_WGI, confidence: high)
By appropriately adjusting the amount, latitude, altitude, and timing of the aerosol injection, modelling studies suggest that SAI is conceptually able to achieve some desired combination of radiative forcing and climate response (IPCC AR6_WGI, confidence: medium)
Relative to the high-GHG climate, it is likely that MCB would increase precipitation over tropical land due to the inhomogeneous forcing pattern of MCB over ocean and land (IPCC AR6_WGI, confidence: medium)
For the same amount of global mean cooling, different SRM options would cause different patterns of climate change (IPCC AR6_WGI, confidence: medium)
There is an offset of continued warming following cessation of emissions by continued CO 2 removal by natural sinks (IPCC AR6_WGI, confidence: high)
Changes in climate at 2300 have impacts and commitments beyond this timeframe (IPCC AR6_WGI, confidence: high)
Non-CO 2 forcing and feedbacks remain important by 2300 (IPCC AR6_WGI, confidence: high)
GSAT differences between SSP5-3.4-overshoot and SSP1-2.6 peak during the 21st century but decline to less than about 0.25°C after 2150 (IPCC AR6_WGI, confidence: medium)
For SSP1-2.6, such a high-warming storyline implies warming well above rather than well below 2°C (IPCC AR6_WGI, confidence: high)
Irrespective of scenario, high-warming storylines imply changes in many aspects of the climate system that exceed the patterns associated with the best estimate of GSAT changes by up to more than 50% (IPCC AR6_WGI, confidence: high)
The Human Perturbation of the Carbon and Biogeochemical Cycles Global mean concentrations for well-mixed GHGs (CO 2, CH 4 and N 2O) in 2019 correspond to increases of about 47%, 156%, and 23%, respectively, above the levels in 1750 (representative of the pre-industrial era) (IPCC AR6_WGI, confidence: high)
Current atmospheric concentrations of the three GHGs are higher than at any point in the last 800,000 years, and in 2019 reached 409.9 parts per million (ppm) of CO2, 1866.3 parts per billion (ppb) of CH4, and 332.1 ppb of N2O (IPCC AR6_WGI, confidence: very high)
Current CO 2 concentrations in the atmosphere are also unprecedented in the last 2 million years (IPCC AR6_WGI, confidence: high)
In the past 60 million years, there have been periods in Earth’s history when CO 2 concentrations were significantly higher than at present, but multiple lines of evidence show that the rate at which CO 2 has increased in the atmosphere during 1900–2019 is at least 10 times faster than at any other time during the last 800,000 years (high confidence), and 4–5 times faster than during the last 56 million years (IPCC AR6_WGI, confidence: low)
During the last measured decade, global average annual anthropogenic emissions of CO 2, CH 4, and N 2O, reached the highest levels in human history at 10.9 ± 0.9 petagrams of carbon per year (PgC yr–1, 2010–2019), 335–383 teragrams of methane per year (TgCH 4 yr–1, 2008–2017), and 4.2–11.4 teragrams of nitrogen per year (TgN yr–1, 2007–2016), respectively (IPCC AR6_WGI, confidence: high)
The ocean and land sinks of CO 2 have continued to grow over the past six decades in response to increasing anthropogenic CO 2 emissions (IPCC AR6_WGI, confidence: high)
Interannual and decadal variability of the regional and global ocean and land sinks indicate that these sinks are sensitive to climate conditions and therefore to climate change (IPCC AR6_WGI, confidence: high)
However, the effects of these changes are not yet reflected in a weakening trend of the contemporary (1960–2019) ocean sink (IPCC AR6_WGI, confidence: high)
The multi-decadal growth trend in atmospheric CH 4 is dominated by anthropogenic activities (high confidence), and the growth since 2007 is largely driven by emissions from both fossil fuels and agriculture (dominated by livestock) (IPCC AR6_WGI, confidence: medium)
This increase is dominated by anthropogenic emissions, which have increased by 30% between the 1980s and the most recent observational decade (2007–2016) (IPCC AR6_WGI, confidence: high)
Increased use of nitrogen fertilizer and manure contributed to about two-thirds of the increase during the 1980–2016 period, with the fossil fuels/industry, biomass burning, and wastewater accounting for much of the rest (IPCC AR6_WGI, confidence: high)
This is attributed to the effect of larger surface warming in CMIP6 models, which increases ocean stratification and reduces ventilation (IPCC AR6_WGI, confidence: medium)
More than half of the latest CMIP6 ESMs include nutrient limitations on the carbon cycle, but these models still project increasing tropical land carbon (medium confidence) and increasing global land carbon (IPCC AR6_WGI, confidence: high)
Under very high emissions scenarios such as SSP5-8.5, ecosystem carbon losses due to warming lead the land to transition from a carbon sink to a source (medium confidence), while the ocean is expected to remain a sink (IPCC AR6_WGI, confidence: high)
In scenarios with moderate net negative CO 2 emissions, and CO 2 concentrations declining during the 21st century (e.g., SSP1-2.6), the land sink transitions to a net source in decades to a few centuries after CO 2 emissions become net negative, while the ocean remains a sink (IPCC AR6_WGI, confidence: low)
Under scenarios with large net negative CO 2 emissions and rapidly declining CO 2 concentrations (e.g., SSP5-3.4-OS (overshoot)), both land and ocean switch from a sink to a transient source during the overshoot period (IPCC AR6_WGI, confidence: medium)
Models project that, over the 21st century, the combined feedback of 0.02–0.09 W m–2 °C–1 is comparable to the effect of a CO 2 release of 5–18 petagrams of carbon equivalent per °C (PgCeq °C–1) (IPCC AR6_WGI, confidence: low)
The probability of crossing uncertain regional thresholds (e.g., high severity fires, forest dieback) increases with climate change (IPCC AR6_WGI, confidence: high)
Possible abrupt changes and tipping points in biogeochemical cycles lead to additional uncertainty in 21st century GHG concentrations, but these are very likely to be smaller than the uncertainty associated with future anthropogenic emissions (IPCC AR6_WGI, confidence: high)
The fraction of CO2 removed that remains out of the atmosphere, a measure of CDR effectiveness, decreases slightly with increasing amount of removal (medium confidence) and decreases strongly if CDR is applied at lower CO 2 concentrations (IPCC AR6_WGI, confidence: medium)
The net effect of this asymmetry on the global surface temperature is poorly constrained due to low agreement between models (IPCC AR6_WGI, confidence: low)
These side effects and associated Earth system feedbacks can decrease carbon uptake and/or change local and regional climate, and in turn limit the CO 2 sequestration and cooling potential of specific CDR methods (IPCC AR6_WGI, confidence: medium)
Deployment of CDR, particularly on land, can also affect water quality and quantity, food production and biodiversity, with consequences for the achievement of related sustainable development goals (IPCC AR6_WGI, confidence: high)
These effects are often highly dependent on local context, management regime, prior land use, and scale of deployment (IPCC AR6_WGI, confidence: high)
A wide range of co-benefits are obtained with methods that seek to restore natural ecosystems or improve soil carbon (IPCC AR6_WGI, confidence: high)
The biogeochemical effects of terminating CDR are expected to be small for most CDR methods (IPCC AR6_WGI, confidence: medium)
SRM acts to cool the planet relative to unmitigated climate change, which would increase the land sink by reducing plant and soil respiration and slow the reduction of ocean carbon uptake due to warming (IPCC AR6_WGI, confidence: medium)
SRM would not counteract or stop ocean acidification (IPCC AR6_WGI, confidence: high)
The sudden and sustained termination of SRM would rapidly increase global warming, with the return of positive and negative effects on the carbon sinks (IPCC AR6_WGI, confidence: very high)
Increasing global net land CO 2 sink since the 1980s is mainly driven by the fertilization effect from rising atmospheric CO 2 concentrations (Schimel et al., 2015; Sitch et al., 2015; Fernández-Martínez et al., 2019; O’Sullivan et al., 2019; Tagesson et al., 2020; Walker et al., 2021) (IPCC AR6_WGI, confidence: medium)
Multiple lines of evidence suggest that WUE has increased in near proportionality to atmospheric CO 2 (IPCC AR6_WGI, confidence: high)
Increased CO 2 concentrations alleviate the effects of water deficits on plant productivity (IPCC AR6_WGI, confidence: medium)
In conclusion, extensive deployment of BECCS and afforestation/reforestation will require larger amounts of freshwater resources than used by the previous vegetation, altering the water cycle at regional scales (IPCC AR6_WGI, confidence: high)
Consequences of high water consumption on downstream uses, biodiversity, and regional climate depend on prior land cover, background climate conditions, and scale of deployment (IPCC AR6_WGI, confidence: high)
Over the industrial era (1750–2019), the total cumulative CO 2 fossil fuel and industry emissions were 445 ± 20 PgC, and the LULUCF flux (= net land-use change in Figure 5.12) was 240 ± 70 PgC (IPCC AR6_WGI, confidence: medium)
The net export of carbon from the terrestrial domain to the open oceans is estimated to be 0.80 PgC yr–1 (IPCC AR6_WGI, confidence: medium)
Although there is evidence that regional human activities and global warming both increase inland water CH 4 emissions (Beaulieu et al., 2019), the increase in the decadal emissions since AR5 (Ciais et al., 2013) rather reflect improvements in the estimate (IPCC AR6_WGI, confidence: medium)
These contrasting lines of evidence suggest that OH changes may have had a small moderating influence on methane growth since 2007 (IPCC AR6_WGI, confidence: low)
Isotopic composition observations and inventory data suggest that concurrent emissions changes from both fossil fuels and agriculture are playing roles in the resumed CH 4 growth since 2007 (IPCC AR6_WGI, confidence: high)
Shorter-term decadal variability is predominantly driven by the influence of El Niño–Southern Oscillation on emissions from wetlands and biomass burning (Cross-Chapter Box 5.2, Figure 2), and loss due to OH variations (IPCC AR6_WGI, confidence: medium)