Editing IPCC:AR6/SYR/Longer-Report (section)

==== 2.1.1. Observed Warming and its Causes ====

<div id="h3-1-siblings" class="h3-siblings"></div>

'''Global surface temperature was around 1.1°C above 1850–1900 in 2011–2020 (1.09 [0.95 to 1.20]°C)''' '''[[#footnote-093|64]] , with larger increases over land (1.59 [1.34 to 1.83]°C) than over the ocean (0.88 [0.68 to 1.01]°C)''' '''[[#footnote-092|65]] . Observed warming is human- caused, with warming from greenhouse gases (GHG), dominated by CO''' '''2 and methane (CH''' '''4), partly masked by aerosol cooling (Figure 2.1)''' . Global surface temperature in the first two decades of the 21st century (2001–2020) was 0.99 [0.84 to 1.10]°C higher than 1850–1900. Global surface temperature has increased faster since 1970 than in any other 50-year period over at least the last 2000 years ( ''high confidence'' ). The ''likely'' range of total human-caused global surface temperature increase from 1850–1900 to 2010–2019 '''[[#footnote-091|66]]''' is 0.8°C to 1.3°C, with a best estimate of 1.07°C. It is ''likely'' that well-mixed GHGs '''[[#footnote-090|67]]''' contributed a warming of 1.0°C to 2.0°C, and other human drivers (principally aerosols) contributed a cooling of 0.0°C to 0.8°C, natural (solar and volcanic) drivers changed global surface temperature by ±0.1°C and internal variability changed it by ±0.2°C. { ''WGI SPM A.1, WGI SPM A.1.2, WGI SPM A.1.3, WGI SPM A.2.2, WGI Figure SPM.2; SRCCL TS.2'' }

Observed increases in well-mixed GHG concentrations since around 1750 are unequivocally caused by GHG emissions from human activities. Land and ocean sinks have taken up a near-constant proportion (globally about 56% per year) of CO 2 emissions from human activities over the past six decades, with regional differences ( high confidence ) . In 2019, atmospheric CO 2 concentrations reached 410 parts per million (ppm), CH 4 reached 1866 parts per billion (ppb) and nitrous oxide ( N 2 O ) reached 332 ppb [[#footnote-089|68]] . Other major contributors to warming are tropospheric ozone (O 3 ) and halogenated gases. Concentrations of CH 4 and N 2 O have increased to levels unprecedented in at least 800,000 years ( very high confidence ) , and there is high confidence that current CO 2 concentrations are higher than at any time over at least the past two million years. Since 1750, increases in CO 2 (47%) and CH 4 (156%) concentrations far exceed – and increases in N 2 O (23%) are similar to – the natural multi-millennial changes between glacial and interglacial periods over at least the past 800,000 years ( very high confidence ) . The net cooling effect which arises from anthropogenic aerosols peaked in the late 20th century ( high confidence ) . { WGI SPM A1.1, WGI SPM A1.3, WGI SPM A.2.1, WGI Figure SPM.2, WGI TS 2.2, WGI 2ES, WGI Figure 6.1 }

<div id="figure-2-1" class="_idGenObjectStyleOverride-2 figure-cont"></div>

[[File:091ec207e6eb5e141653abb239b1a8a8 IPCC_AR6_SYR_Figure_2_1.png]]
'''Figure 2.1: The causal chain from emissions to resulting warming of the climate system.''' Emissions of GHG have increased rapidly over recent decades '''(panel (a))''' . Global net anthropogenic GHG emissions include CO 2 from fossil fuel combustion and industrial processes (CO 2 -FFI) (dark green); net CO 2 from land use, land-use change and forestry (CO 2 -LULUCF) (green); CH 4 ; N 2 O; and fluorinated gases (HFCs, PFCs, SF 6 , NF 3 ) (light blue). These emissions have led to increases in the atmospheric concentrations of several GHGs including the three major well-mixed GHGs CO 2 , CH 4 and N 2 O '''(panel (b)''' , annual values). To indicate their relative importance each subpanel’s vertical extent for CO 2 , CH 4 and N 2 O is scaled to match the assessed individual direct effect (and, in the case of CH 4 indirect effect via atmospheric chemistry impacts on tropospheric ozone) of historical emissions on temperature change from 1850–1900 to 2010–2019. This estimate arises from an assessment of effective radiative forcing and climate sensitivity. The global surface temperature (shown as annual anomalies from a 1850–1900 baseline) has increased by around 1.1°C since 1850–1900 '''(panel (c))''' . The vertical bar on the right shows the estimated temperature ''(very likely range)'' during the warmest multi-century period in at least the last 100,000 years, which occurred around 6500 years ago during the current interglacial period (Holocene). Prior to that, the next most recent warm period was about 125,000 years ago, when the assessed multi-century temperature range [0.5°C to 1.5°C] overlaps the observations of the most recent decade. These past warm periods were caused by slow (multi-millennial) orbital variations. Formal detection and attribution studies synthesise information from climate models and observations and show that the best estimate is that all the warming observed between 1850–1900 and 2010–2019 is caused by humans '''(panel (d))''' . The panel shows temperature change attributed to: total human influence; its decomposition into changes in GHG concentrations and other human drivers (aerosols, ozone and land-use change (land-use reflectance)); solar and volcanic drivers; and internal climate variability. Whiskers show ''likely'' ranges. ''{ WGI SPM A.2.2, WGI Figure SPM.1, WGI Figure SPM.2, WGI TS2.2, WGI 2.1; WGIII Figure SPM.1, WGIII A.III.II.2.5.1 }''

[https://www.ipcc.ch/figures/figure-2-1 ]

'''Average annual GHG emissions during 2010 –2019 were higher than in any previous decade, but the rate of growth between 2010 and 2019 (1.3% yr''' -1 ) was lower than that between 2000 and 2009 (2.1% yr -1 ) '''[[#footnote-088|69]] .''' Historical cumulative net CO 2 emissions from 1850 to 2019 were 2400 ±240 GtCO 2 . Of these, more than half (58%) occurred between 1850 and 1989 [1400 ±195 GtCO 2 ], and about 42% between 1990 and 2019 [1000 ±90 GtCO 2 ]. Global net anthropogenic GHG emissions have been estimated to be 59±6.6 GtCO 2 -eq in 2019, about 12% (6.5 GtCO 2 -eq) higher than in 2010 and 54% (21 GtCO 2 -eq) higher than in 1990. By 2019, the largest growth in gross emissions occurred in CO 2 from fossil fuels and industry (CO 2 -FFI) followed by CH 4 , whereas the highest relative growth occurred in fluorinated gases (F-gases), starting from low levels in 1990. ( ''high confidence'' ) { ''WGIII SPM B1.1, WGIII SPM B.1.2, WGIII SPM B.1.3, WGIII Figure SPM.1, WGIII Figure SPM.2'' }

<div id="figure-2-1" class="_idGenObjectStyleOverride-2 figure-cont"></div>

[[File:94a7f0eb0d41f519dc02f8fdd48dfc77 IPCC_AR6_SYR_Figure_2_2.png]]
'''Figure 2.2: Regional GHG emissions, and the regional proportion of total cumulative production-based CO''' '''2''' emissions from 1850 to 2019. Panel (a) shows the share of historical cumulative net anthropogenic CO 2 emissions per region from 1850 to 2019 in GtCO 2 . This includes CO 2 -FFI and CO 2 -LULUCF. Other GHG emissions are not included. CO 2 -LULUCF emissions are subject to high uncertainties, reflected by a global uncertainty estimate of ±70% (90% confidence interval). '''Panel (b)''' shows the distribution of regional GHG emissions in tonnes CO 2 -eq per capita by region in 2019. GHG emissions are categorised into: CO 2 -FFI; net CO 2 -LULUCF; and other GHG emissions (CH 4 , N 2 O, fluorinated gases, expressed in CO 2 -eq using GWP100-AR6). The height of each rectangle shows per capita emissions, the width shows the population of the region, so that the area of the rectangles refers to the total emissions for each region. Emissions from international aviation and shipping are not included. In the case of two regions, the area for CO 2 -LULUCF is below the axis, indicating net CO 2 removals rather than emissions. '''Panel (c)''' shows global net anthropogenic GHG emissions by region (in GtCO 2 -eq yr ''–1'' (GWP100-AR6)) for the time period 1990–2019. Percentage values refer to the contribution of each region to total GHG emissions in each respective time period. The single-year peak of emissions in 1997 was due to higher CO 2 -LULUCF emissions from a forest and peat fire event in South East Asia. Regions are as grouped in Annex II of WGIII. '''Panel (d)''' shows population, gross domestic product (GDP) per person, emission indicators by region in 2019 for total GHG per person, and total GHG emissions intensity, together with production-based and consumption-based CO 2 -FFI data, which is assessed in this report up to 2018. Consumption-based emissions are emissions released to the atmosphere in order to generate the goods and services consumed by a certain entity (e.g., region). Emissions from international aviation and shipping are not included. ''{ WGIII Figure SPM.2 }''

[https://www.ipcc.ch/figures/figure-2-2 ]

'''Regional contributions to global human-caused GHG emissions continue to differ widely.''' Historical contributions of CO 2 emissions vary substantially across regions in terms of total magnitude, but also in terms of contributions to CO 2 -FFI (1650 ± 73 GtCO 2 -eq) and net CO 2 -LULUCF (760 ± 220 GtCO 2 -eq) emissions (Figure 2.2). Variations in regional and national per capita emissions partly reflect different development stages, but they also vary widely at similar income levels. Average per capita net anthropogenic GHG emissions in 2019 ranged from 2.6 tCO 2 -eq to 19 tCO 2 -eq across regions (Figure 2.2). Least Developed Countries (LDCs) and Small Island Developing States (SIDS) have much lower per capita emissions (1.7 tCO 2 -eq and 4.6 tCO 2 -eq, respectively) than the global average (6.9 tCO 2 -eq), excluding CO 2 -LULUCF. Around 48% of the global population in 2019 lives in countries emitting on average more than 6 tCO 2 -eq per capita, 35% of the global population live in countries emitting more than 9 tCO 2 -eq per capita '''[[#footnote-087|70]]''' (excluding CO 2 -LULUCF) while another 41% live in countries emitting less than 3 tCO 2 -eq per capita. A substantial share of the population in these low-emitting countries lack access to modern energy services. ( ''high confidence'' ) { ''WGIII SPM B.3, WGIII SPM B3.1, WGIII SPM B.3.2, WGIII SPM B.3.3'' }

'''Net GHG emissions have increased since 2010 across all major sectors (''' '''''high confidence).''''' In 2019, approximately 34% (20 GtCO 2 -eq) of net global GHG emissions came from the energy sector, 24% (14 GtCO 2 -eq) from industry, 22% (13 GtCO 2 -eq) from AFOLU, 15% (8.7 GtCO 2 -eq) from transport and 6% (3.3 GtCO 2 -eq) from buildings '''[[#footnote-086|71]]''' ( ''high confidence'' ). Average annual GHG emissions growth between 2010 and 2019 slowed compared to the previous decade in energy supply (from 2.3% to 1.0%) and industry (from 3.4% to 1.4%) but remained roughly constant at about 2% yr ''–1'' in the transport sector ( ''high confidence'' ). About half of total net AFOLU emissions are from CO 2 LULUCF, predominantly from deforestation ( ''medium confidence'' ). Land overall constituted a net sink of –6.6 (±4.6) GtCO 2 yr ''–1'' for the period 2010–2019 '''[[#footnote-085|72]]''' ( ''medium confidence'' ). { ''WGIII SPM B.2, WGIII SPM B.2.1, WGIII SPM B.2.2, WGIII TS 5.6.1'' } .

'''Human-caused climate change is a consequence of more than a century of net GHG emissions from energy use, land-use and land use change, lifestyle and patterns of consumption, and production.''' Emissions reductions in CO 2 from fossil fuels and industrial processes (CO 2 -FFI), due to improvements in energy intensity of GDP and carbon intensity of energy, have been less than emissions increases from rising global activity levels in industry, energy supply, transport, agriculture and buildings. The 10% of households with the highest per capita emissions contribute 34–45% of global consumption-based household GHG emissions, while the middle 40% contribute 40–53%, and the bottom 50% contribute 13–15%. An increasing share of emissions can be attributed to urban areas (a rise from about 62% to 67–72% of the global share between 2015 and 2020). The drivers of urban GHG emissions '''[[#footnote-084|73]]''' are complex and include population size, income, state of urbanisation and urban form. ( ''high confidence'' ) { ''WGIII SPM B.2, WGIII SPM B.2.3, WGIII SPM B.3.4, WGIII SPM D.1.1'' }

<div id="2.2.3" class="h3-container"></div>

<span id="observed-climate-system-changes-and-impacts-to-date"></span>