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1,100 | AR6_WGI | 883 | 25 | In summary, the net aviation ERF is assessed to be +0.1 W m–2 (±0.045) for the year 2018 | low | 0 | train |
1,101 | AR6_WGI | 883 | 27 | The climate response to SLCF‑related aviation terms exhibits substantial spatio‑temporal heterogeneity in characteristics | high | 2 | train |
1,102 | AR6_WGI | 883 | 28 | Overall, cirrus and contrail cirrus warming, as well as NO x‑induced ozone increase, induce strong but short‑lived warming contributions to the GSAT response 10 years after a one‑year pulse of present‑day aviation emissions (medium confidence), while CO 2 both gives a warming effect in the near term and dominates the long‑term warming impact | high | 2 | train |
1,103 | AR6_WGI | 883 | 39 | In summary, a year’s worth of present‑day global shipping emissions (i.e., without the implementation of the 2020 clean fuel standards) cause a net global cooling (–0.0024 ± 0.0025°C) on 10–20 year time horizons | high | 2 | train |
1,104 | AR6_WGI | 884 | 12 | In summary, the present‑day global land‑based transport pulse emissions cause a net global warming on all time scales (high confidence) and are detrimental to air quality | high | 2 | train |
1,105 | AR6_WGI | 884 | 29 | By far the largest 10‑year GSAT effects are from the energy production (fossil fuel mining and distribution), agriculture and waste management sectors | high | 2 | train |
1,106 | AR6_WGI | 884 | 31 | On the 10‑year time horizon, other net warming sectors are residential fossil fuel and energy combustion (dominated by CO 2) and aviation and residential biofuel (dominated by SLCFs and cloud) | medium | 1 | train |
1,107 | AR6_WGI | 885 | 5 | In terms of source regions, the largest contributions to net short‑ term warming are caused by emissions in Eastern Asia, Latin America and North America, followed by Africa, Eastern Europe, West‑Central Asia and South East Asia | medium | 1 | train |
1,108 | AR6_WGI | 885 | 9 | Overall, the global sectors that contribute the largest warming on short time scales are the methane‑dominated sources, that is energy production (fossil fuel mining and distribution), and agriculture and waste management | high | 2 | train |
1,109 | AR6_WGI | 885 | 10 | On short time scales, other net warming sectors are residential fossil fuel and energy combustion (dominated by CO 2), and aviation and residential biofuel (dominated by SLCFs) | medium | 1 | train |
1,110 | AR6_WGI | 885 | 11 | On short time scales, global emissions from industry and shipping cause a net cooling effect despite a considerable warming from CO 2 emissions | high | 2 | train |
1,111 | AR6_WGI | 885 | 12 | On longer time horizons, the sectors that contribute the largest warming are energy combustion and industry due to the large CO 2 emissions | high | 2 | train |
1,112 | AR6_WGI | 885 | 26 | Residential and commercial cooking and heating are among the most important anthropogenic sources of ambient PM 2.5, except in the Middle East and Asia‑Pacific Developed (high confidence) and agriculture is the dominant source in Europe and North America | medium | 1 | train |
1,113 | AR6_WGI | 885 | 27 | Energy and industry are important PM 2.5 contributors in most regions, except Africa | high | 2 | train |
1,114 | AR6_WGI | 891 | 1 | Additional policies (e.g., access to clean energy, waste management) envisaged to attain SDGs bring complementary SLCF reduction | high | 2 | train |
1,115 | AR6_WGI | 891 | 2 | Sustained methane mitigation, wherever it occurs, stands out as an option that combines near ‑ and long‑term gains on surface temperature (high confidence) and leads to an air pollution benefit by reducing ozone levels globally | high | 2 | train |
1,116 | AR6_WGI | 891 | 21 | Emissions Global fossil CO 2 emissions are estimated to have declined by 7% | medium | 1 | train |
1,117 | AR6_WGI | 892 | 8 | Anthropogenic NO x emissions, which are largely from the transport sector, are estimated to have decreased by a maximum of 35% in April | medium | 1 | train |
1,118 | AR6_WGI | 892 | 18 | Except for ozone, temporary improvement of air quality during lockdown periods was observed in most regions of the world (high confidence), resulting from a combination of interannual meteorological variability and the impact of COVID‑19 containment measures | high | 2 | train |
1,119 | AR6_WGI | 892 | 19 | Estimated air pollution reductions associated with lockdown periods are lower than what can be expected from integrated mitigation policy leading to lasting reductions | medium | 1 | train |
1,120 | AR6_WGI | 893 | 17 | The range in peak global mean ERF in spring 2020 was [0.025 to 0.2] W m–2 | medium | 1 | train |
1,121 | AR6_WGI | 893 | 18 | By the end of 2020, the ERF was at half the peak value | medium | 1 | train |
1,122 | AR6_WGI | 893 | 19 | Climate responses Changes in atmospheric composition due to COVID‑19 emissions reductions are not thought to have caused a detectable change in global temperature or rainfall in 2020 | high | 2 | train |
1,123 | AR6_WGI | 894 | 22 | Simulated GSAT and rainfall changes are unlikely to be detectable in observations | high | 2 | train |
1,124 | AR6_WGI | 898 | 16 | Consequently, SSPs span a wider range of SLCF emissions than considered in the RCPs, better covering the diversity of future options in air pollution management and SLCF‑induced climate effects | high | 2 | train |
1,125 | AR6_WGI | 899 | 1 | However, this decrease is twice as large when methane emissions are abated simultaneously (SSP3‑7.0‑lowSLCF‑lowCH 4), underlying the importance of methane emissions reduction as an important lever to reduce ozone pollution | high | 2 | train |
1,126 | AR6_WGI | 900 | 1 | In the latter case, PM levels are estimated to increase until 2050 over large parts of Asia and surface ozone pollution worsens over all continental areas throughout the whole century | high | 2 | train |
1,127 | AR6_WGI | 900 | 2 | In scenarios without climate change mitigation but with strong air pollution control (SSP5‑8.5), high methane levels hamper the decline in global surface ozone in the near term and only PM levels decrease | high | 2 | train |
1,128 | AR6_WGI | 904 | 29 | Furthermore, under SSP5‑8.5, HFCs induce a warming of 0.06°C with a very likely range of [0.04 to 0.08] °C in 2050 and 0.2 [0.1 to 0.3] °C by the end of the 21st century, relative to 2019, while under SSP1‑2.6, warming due to HFCs is negligible (below 0.02°C) | high | 2 | train |
1,129 | AR6_WGI | 905 | 2 | Methane mitigation that also reduces tropospheric ozone, stands out as an option that combines near‑ and long‑term gains on surface temperature | high | 2 | train |
1,130 | AR6_WGI | 905 | 14 | The assessment shows that both strong air pollution control and strong climate change mitigation, implemented independently, lead to a large reduction of exposure to PM 2.5 and ozone by the end of the century | high | 2 | train |
1,131 | AR6_WGI | 905 | 15 | However, implementation of air pollution control, relying on the deployment of existing technologies, leads to benefits more rapidly than climate change mitigation | high | 2 | train |
1,132 | AR6_WGI | 905 | 16 | Notably, under the underlying SSP3 context, significant parts of the population remain exposed to air quality exceeding the WHO guidelines for PM 2.5 over the whole century | high | 2 | train |
1,133 | AR6_WGI | 908 | 1 | In summary, the warming induced by SLCF changes is stable after 2040 in the WGI core set of SSP scenarios associated with lower global air pollution as long as methane emissions are also mitigated, but the overall warming induced by SLCF changes is higher in scenarios in which air quality continues to deteriorate (caused by growing fossil fuel use and limited air pollution control) | high | 2 | train |
1,134 | AR6_WGI | 908 | 5 | Sustained methane mitigation, wherever it occurs, stands out as an option that combines near ‑ and long‑term gains on surface temperature (high confidence) and leads to air pollution benefits by reducing surface ozone level globally | high | 2 | train |
1,135 | AR6_WGI | 908 | 6 | Strong air pollution control as well as strong climate change mitigation, implemented independently, lead to large reduction of the exposure to air pollution by the end of the century | high | 2 | train |
1,136 | AR6_WGI | 908 | 7 | Implementation of air pollution control, relying on the deployment of existing technologies, leads more rapidly to air ‑quality benefits than climate change mitigation which requires systemic changes but, in both cases, significant parts of the population remain exposed to air pollution exceeding the WHO guidelines | high | 2 | train |
1,137 | AR6_WGI | 941 | 13 | Energy will continue to accumulate in the Earth system until at least the end of the 21st century, even under strong mitigation scenarios, and will primarily be observed through ocean warming and associated with continued sea level rise through thermal expansion | high | 2 | train |
1,138 | AR6_WGI | 941 | 19 | More comprehensive analysis of inventory components and cross-validation of global heating rates from satellite and in situ observations lead to a strengthened assessment relative to AR5 | high | 2 | train |
1,139 | AR6_WGI | 941 | 23 | Both estimates are consistent with an independent observation-based assessment of the global energy increase of 284 [96 to 471] ZJ, (very likely range) expressed relative to the estimated 1850–1900 Earth energy imbalance | high | 2 | train |
1,140 | AR6_WGI | 941 | 25 | These trends are neither a local phenomenon nor a measurement artefact | high | 2 | train |
1,141 | AR6_WGI | 941 | 26 | Multi-decadal variation in anthropogenic aerosol emissions are thought to be a major contributor | medium | 1 | train |
1,142 | AR6_WGI | 941 | 27 | The downward and upward thermal radiation at the surface has increased in recent decades, in line with increased greenhouse gas concentrations and associated surface and atmospheric warming and moistening | medium | 1 | train |
1,143 | AR6_WGI | 941 | 31 | For carbon dioxide, the adjustments include the physiological effects on vegetation | high | 2 | train |
1,144 | AR6_WGI | 942 | 3 | The 0.59 W m–2 increase in ERF from greenhouse gases is partly offset by a better-constrained assessment of total aerosol ERF that is more strongly negative than in AR5, based on multiple lines of evidence | high | 2 | train |
1,145 | AR6_WGI | 942 | 4 | Changes in surface reflectance from land-use change, deposition of light-absorbing particles on ice and snow, and contrails and aviation-induced cirrus have also contributed to the total anthropogenic ERF over the industrial era, with –0.20 [–0.30 to –0.10] W m–2 (medium confidence), +0.08 [0 to 0.18] W m–2 (low confidence) and +0.06 [0.02 to 0.10] W m–2 | low | 0 | train |
1,146 | AR6_WGI | 942 | 10 | The estimated ERF for methane has slightly increased due to a combination of increases from improved spectroscopic treatments being somewhat offset by accounting for adjustments | high | 2 | train |
1,147 | AR6_WGI | 942 | 12 | The ERF due to aerosol–cloud interactions (ERFaci) contributes most to the magnitude of the total aerosol ERF (high confidence) and is assessed to be –1.0 [–1.7 to –0.3] W m–2 (medium confidence), with the remainder due to aerosol–radiation interactions (ERFari), assessed to be –0.3 [–0.6 to 0.0] W m–2 | medium | 1 | train |
1,148 | AR6_WGI | 942 | 17 | It is also assessed to be smaller in magnitude at –1.1 [–1.7 to –0.4] W m–2, primarily due to recent emissions changes | medium | 1 | train |
1,149 | AR6_WGI | 942 | 22 | A net negative cloud feedback is very unlikely | high | 2 | train |
1,150 | AR6_WGI | 942 | 27 | Furthermore, on long time scales the ice-sheet feedback parameter is very likely positive, promoting additional warming on millennial time scales as ice sheets come into equilibrium with the forcing | high | 2 | train |
1,151 | AR6_WGI | 942 | 29 | This new understanding, along with updated estimates of historical temperature change, ERF, and Earth’s energy imbalance, reconciles previously disparate ECS estimates | high | 2 | train |
1,152 | AR6_WGI | 942 | 31 | Warming over the instrumental record provides robust constraints on the lower end of the ECS range | high | 2 | train |
1,153 | AR6_WGI | 943 | 7 | These higher ECS and TCR values can, in some models, be traced to changes in extra-tropical cloud feedbacks that have emerged from efforts to reduce biases in these clouds compared to satellite observations | medium | 1 | train |
1,154 | AR6_WGI | 943 | 11 | The CMIP models with the highest ECS and TCR values provide insights into low-likelihood, high-impact outcomes, which cannot be excluded based on currently available evidence | high | 2 | train |
1,155 | AR6_WGI | 943 | 14 | The calculated GSAT change is composed of a well-mixed greenhouse gas 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), a cooling of –0.50 [–0.22 to –0.96] °C from aerosol effects (medium confidence), and a –0.06 [–0.15 to +0.01] °C contribution from surface reflectance changes from land-use change and light-absorbing particles on ice and snow | medium | 1 | train |
1,156 | AR6_WGI | 943 | 15 | Changes in solar and volcanic activity are assessed to have together contributed a small change of –0.02 [–0.06 to +0.02] °C since 1750 | medium | 1 | train |
1,157 | AR6_WGI | 943 | 18 | Global ocean heat uptake is a smaller source of uncertainty in centennial-time scale surface warming | high | 2 | train |
1,158 | AR6_WGI | 943 | 22 | When used for multi-scenario experiments, calibrated physically based emulators can adequately reflect assessments regarding future GSAT from Earth system models and/or other lines of evidence | high | 2 | train |
1,159 | AR6_WGI | 943 | 24 | The causes of this polar amplification are well understood, and the evidence is stronger than at the time of AR5, supported by better agreement between modelled and observed polar amplification during warm paleo time periods | high | 2 | train |
1,160 | AR6_WGI | 943 | 26 | The rate of Arctic surface warming will continue to exceed the global average over this century | high | 2 | train |
1,161 | AR6_WGI | 943 | 31 | Metrics for methane from fossil fuel sources account for the extra fossil CO 2 that these emissions contribute to the atmosphere and so have slightly higher emissions metric values than those from biogenic sources | high | 2 | train |
1,162 | AR6_WGI | 944 | 1 | By contrast, if emissions are weighted by their 100-year GWP or GTP values, different multi-gas emissions pathways with the same aggregated CO 2 equivalent emissions rarely lead to the same estimated temperature outcome | high | 2 | train |
1,163 | AR6_WGI | 944 | 5 | In contrast, reaching net zero GHG emissions when quantified using new emissions metrics such as CGTP or GWP* would lead to approximate temperature stabilization | high | 2 | train |
1,164 | AR6_WGI | 951 | 31 | In summary, since AR5, the magnitudes of the global mean energy budget components have been quantified more accurately, not only at the TOA, but also at the Earth’s surface, where independent estimates of the radiative components have converged | high | 2 | train |
1,165 | AR6_WGI | 953 | 4 | In summary, variations in the energy exchange between Earth and space can be accurately tracked since the advent of improved observations since the year 2000 (high confidence), while reconstructions indicate that the Earth’s energy imbalance was larger in the 2000s than in the 1985–1999 period | high | 2 | train |
1,166 | AR6_WGI | 953 | 34 | The assessed changes in the global energy inventory (Box 7.2, Figure 1, and Table 7.1) yields an average value for Earth’s energy imbalance (N in Box 7.1, Equation 7.1) of 0.57 [0.43 to 0.72] W m–2 for the period 1971–2018, expressed relative to Earth’s surface area | high | 2 | train |
1,167 | AR6_WGI | 953 | 35 | The estimates for the periods 1993–2018 and 2006–2018 yield substantially larger values of 0.72 [0.55 to 0.89] W m–2 and 0.79 [0.52 to 1.06] W m–2, respectively, consistent with the increased radiative forcing from GHGs | high | 2 | train |
1,168 | AR6_WGI | 954 | 1 | To put these numbers in context, the 2006–2018 average Earth system heating is equivalent to approximately 20 times the annual rate of global energy consumption in 2018.1 Consistent with AR5 (Rhein et al., 2013), this Report finds that ocean warming dominates the changes in the global energy inventory | high | 2 | train |
1,169 | AR6_WGI | 954 | 2 | The contributions from the other components across all periods are approximately 5% from land heating, 3% for cryosphere heating and 1% associated with warming of the atmosphere | high | 2 | train |
1,170 | AR6_WGI | 955 | 23 | The origin of these trends is not fully understood, although there is evidence that anthropogenic aerosols have made a substantial contribution | medium | 1 | train |
1,171 | AR6_WGI | 957 | 4 | For the period 1970–2011, AR5 reported that the global energy budget was closed within uncertainties | high | 2 | train |
1,172 | AR6_WGI | 961 | 10 | The physiological adjustments are therefore assessed to make a substantial contribution to the overall tropospheric adjustment for CO 2 | high | 2 | train |
1,173 | AR6_WGI | 961 | 15 | Due to the agreement between the studies and the understanding of the physical mechanisms there is medium confidence in the mechanisms underpinning the tropospheric adjustment, but low confidence in its magnitude.The ERF from doubling CO 2 (2×CO 2) from the 1750 level (278 ppm; Section 2.2.3.3) is assessed to be 3.93 ± 0.47 W m–2 | high | 2 | train |
1,174 | AR6_WGI | 963 | 9 | This does not correspond to the division between ozone production and ozone depletion and is sensitive to the choice of tropopause | high | 2 | train |
1,175 | AR6_WGI | 963 | 11 | This small positive (but with uncertainty encompassing negative values) stratospheric ozone SARF is due to contributions from ozone precursors to lower stratospheric ozone and some of the CMIP6 models showing ozone depletion in the upper stratosphere, where depletion contributes a positive radiative forcing | medium | 1 | train |
1,176 | AR6_WGI | 963 | 12 | As there is insufficient evidence to quantify adjustments, for total ozone the assessed central estimate for ERF is assumed to be equal to SARF | low | 0 | train |
1,177 | AR6_WGI | 963 | 32 | It has increased by 0.49 W m–2 compared to AR5 (reference year 2011) | high | 2 | train |
1,178 | AR6_WGI | 963 | 34 | Changes in the radiative efficiencies (including adjustments) of CO 2, CH 4, N 2O and halogenated compounds have increased the ERF by an additional 0.15 W m–2 compared to the AR5 values | high | 2 | train |
1,179 | AR6_WGI | 963 | 38 | The combined ERF from ozone and stratospheric water vapour has increased since AR5 by 0.10 ± 0.50 W m–2 | high | 2 | train |
1,180 | AR6_WGI | 966 | 22 | Based on the above, IRFari is assessed to be –0.25 ± 0.2 W m–2 | medium | 1 | train |
1,181 | AR6_WGI | 966 | 24 | Adding this small adjustment to our assessed IRFari estimate of –0.25 W m–2, and accounting for additional uncertainty in the adjustments, ERFari is assessed to –0.3 ± 0.3 | medium | 1 | train |
1,182 | AR6_WGI | 968 | 27 | Taking the average across the studies providing IRFaci estimates discussed above and considering the general agreement among estimates (Table 7.7), IRFaci is assessed to be –0.7 ± 0.5 W m–2 | medium | 1 | train |
1,183 | AR6_WGI | 969 | 9 | These three studies together suggest a global Cf adjustment that augments ERFaci relative to IRFaci by –0.5 ± 0.4 W m–2 | medium | 1 | train |
1,184 | AR6_WGI | 969 | 18 | Combining IRFaci and the associated adjustments in Cf and LWP (adding uncertainties in quadrature), considering only liquid-water clouds and evidence from satellite observations alone, the central estimate and very likely range for ERFaci is assessed to be –1.0 ± 0.7 W m–2 | medium | 1 | train |
1,185 | AR6_WGI | 969 | 37 | There is thus limited evidence and medium agreement for a small negative contribution to ERFaci from anthropogenic INP-induced cirrus modifications | low | 0 | test |
1,186 | AR6_WGI | 969 | 41 | From model-based evidence, ERFaci is assessed to –1.0 ± 0.8 W m–2 | medium | 1 | train |
1,187 | AR6_WGI | 970 | 1 | The strong agreement between the two largely independent lines of evidence increases confidence in the overall assessment of the central estimate and very likely range for ERFaci of –1.0 ± 0.7 W m–2 | medium | 1 | train |
1,188 | AR6_WGI | 970 | 38 | Based solely on energy balance considerations or other observational constraints, it is extremely likely that the total aerosol ERF is negative (high confidence), but extremely unlikely that the total aerosol ERF is more negative than –2.0 W m–2 | high | 2 | train |
1,189 | AR6_WGI | 971 | 18 | 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 | medium | 1 | train |
1,190 | AR6_WGI | 971 | 26 | 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 | medium | 1 | train |
1,191 | AR6_WGI | 971 | 28 | Aerosols are therefore assessed to have contributed an ERF of –1.1 [–1.7 to –0.4] W m–2 over 1750–2019 | medium | 1 | train |
1,192 | AR6_WGI | 972 | 35 | 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 | medium | 1 | train |
1,193 | AR6_WGI | 974 | 6 | 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 | medium | 1 | train |
1,194 | AR6_WGI | 974 | 8 | 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 | medium | 1 | train |
1,195 | AR6_WGI | 974 | 38 | The ERF for volcanic stratospheric aerosols is assessed to be –20 ± 5 W m–2 per unit SAOD | medium | 1 | train |
1,196 | AR6_WGI | 975 | 7 | The stratospheric-temperature-adjusted radiative efficiency for CH 4 is increased by approximately 25% | high | 2 | train |
1,197 | AR6_WGI | 975 | 8 | The tropospheric adjustment is tentatively assessed to be –14% | low | 0 | train |
1,198 | AR6_WGI | 975 | 9 | A +7% tropospheric adjustment has been added to the radiative efficiency for N 2O and +12% to CFC-11 and CFC-12 | low | 0 | train |
1,199 | AR6_WGI | 976 | 4 | However, the total aerosol ERF is assessed to be more negative compared to AR5, due to revised estimates rather than trends | high | 2 | train |
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