Editing IPCC:AR6/WGI/TS (section)

=== TS.2.5 The Cryosphere ===

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'''Over recent decades, widespread loss of snow and ice has been observed, and several elements of the cryosphere are now in states unseen in centuries ( ''high confidence'' ). Human influence was ''very likely'' the main driver of observed reductions in Arctic sea ice since the late 1970s (with late-summer sea ice loss ''likely'' unprecedented for at least 1000 years) and the widespread retreat of glaciers (unprecedented in at least the last 2,000 years, ''medium confidence'' ). Furthermore, human influence ''very likely'' contributed to the observed Northern Hemisphere spring snow cover decrease since 1950.''' '''By contrast, Antarctic sea ice area experienced no significant net change since 1979, and there is only ''low confidence'' in its projected changes. The Arctic Ocean is projected to become practically sea ice-free in late summer under high CO <sub>2</sub> emissions scenarios by the end of the 21st century ( ''high confidence'' ). It is ''virtually certain'' that further warming will lead to further reductions of Northern Hemisphere snow cover, and there is ''high confidence'' that this is also the case for near-surface permafrost volume.''' '''Glaciers will continue to lose mass at least for several decades even if global temperature is stabilized ( ''very high confidence'' ), and mass loss over the 21st century is ''virtually certain'' for the Greenland Ice Sheet and ''likely'' for the Antarctic Ice Sheet. Deep uncertainty persists with respect to the possible evolution of the Antarctic Ice Sheet within the 21st century and beyond, in particular due to the potential instability of the West Antarctic Ice Sheet. Links to chapters 2.3, 3.4, 4.3, 8.3, 9.3–9.6, Box 9.4, 12.4'''
Current Arctic sea ice coverage levels (both annual and late summer) are at their lowest since at least 1850 ( ''high confidence'' ), and for late summer for the past 1000 years ( ''medium confidence'' ). Since the late 1970s, Arctic sea ice area and thickness have decreased in both summer and winter, with sea ice becoming younger, thinner and more dynamic ( ''very high confidence'' ). It is ''very likely'' that anthropogenic forcing, mainly due to greenhouse gas increases, was the main driver of this loss, although new evidence suggests that anthropogenic aerosol forcing has offset part of the greenhouse gas-induced losses since the 1950s ( ''medium confidence'' ). The annual Arctic sea ice area minimum will ''likely'' fall below 1 million km <sup>2</sup> at least once before 2050 under all assessed SSP scenarios. This practically sea ice-free state will become the norm for late summer by the end of the 21st century in high CO <sub>2</sub> emissions scenarios ( ''high confidence'' ). Arctic summer sea ice varies approximately linearly with global surface temperature, implying that there is no tipping point and observed/projected losses are potentially reversible ( ''high'' ''confidence'' ). Links to chapters 2.3.2, 3.4.1, 4.3.2, 9.3.1, 12.4.9

For Antarctic sea ice, there is no significant trend in satellite-observed sea ice area from 1979 to 2020 in both winter and summer, due to regionally opposing trends and large internal variability. Due to mismatches between model simulations and observations, combined with a lack of understanding of reasons for substantial inter-model spread, there is ''low confidence'' in model projections of future Antarctic sea ice changes, particularly at the regional level. Links to chapters 2.3.2, 3.4.1, 9.3.2

In permafrost regions, increases in ground temperatures in the upper 30 m over the past three to four decades have been widespread ( ''high confidence'' ). For each additional 1°C of warming (up to 4°C above the 1850–1900 level), the global volume of perennially frozen ground to 3 m below the surface is projected to decrease by about 25% relative to the present volume ( ''medium confidence'' ). However, these decreases may be underestimated due to an incomplete representation of relevant physical processes in ESMs ( ''low confidence'' ). Seasonal snow cover is treated in Section TS.2.6. Links to chapters 2.3.2, 9.5.2, 12.4.9

There is ''very high confidence'' that, with few exceptions, glaciers have retreated since the second half of the 19th century; this behaviour is unprecedented in at least the last 2000 years ( ''medium confidence'' ). Mountain glaciers ''very likely'' contributed 67.2 [41.8 to 92.6] mm to the observed GMSL change between 1901 and 2018. This retreat has occurred at increased rates since the 1990s, with human influence ''very likely'' being the main driver. Under RCP2.6 and RCP8.5, respectively, glaciers are projected to lose 18% ± 13% and 36% ± 20% of their current mass over the 21st century ( ''medium confidence'' ). Links to chapters 2.3.2, 3.4.3, 9.5.1, 9.6.1

The Greenland Ice Sheet was smaller than at present during the Last Interglacial period (roughly 125,000 years ago) and the mid-Holocene (roughly 6,000 years ago) ( ''high confidence'' ). After reaching a recent maximum ice mass at some point between 1450 and 1850, the ice sheet retreated overall, with some decades ''likely'' close to equilibrium (i.e., mass loss approximately equalling mass gained). It is ''virtually certain'' that the Greenland Ice Sheet has lost mass since the 1990s, with human influence a contributing factor ( ''medium confidence'' ). There is ''high confidence'' that annual mass changes have been consistently negative since the early 2000s. Over the period 1992–2020, Greenland ''likely'' lost 4890 ± 460 Gt of ice, contributing 13.5 ± 1.3 mm to GMSL rise. There is ''high confidence'' that Greenland ice mass losses are increasingly dominated by surface melting and runoff, with large interannual variability arising from changes in surface mass balance. Projections of future Greenland ice-mass loss (Box TS.4, Table 1; Figure TS.11e) are dominated by increased surface melt under all emissions scenarios ( ''high confidence'' ). Potential irreversible long-term loss of the Greenland Ice Sheet, and of parts of the Antarctic Ice Sheet, is assessed in Box TS.9. Links to chapters 2.3.2, 3.4.3, 9.4.1, 9.4.2, 9.6.3, Atlas.11.2

It is ''likely'' that the Antarctic Ice Sheet has lost 2670 ± 530 Gt, contributing 7.4 ± 1.5 mm to GMSL rise over 1992–2020. The total Antarctic ice mass losses were dominated by the West Antarctic Ice Sheet, with combined West Antarctic and Peninsula annual loss rates increasing since about 2000 ( ''very high confidence'' ). Furthermore, it is ''very likely'' that parts of the East Antarctic Ice Sheet have lost mass since 1979. Since the 1970s, snowfall has ''likely'' increased over the western Antarctic Peninsula and eastern West Antarctica, with large spatial and interannual variability over the rest of Antarctica. Mass losses from West Antarctic outlet glaciers, mainly induced by ice shelf basal melt ( ''high confidence'' ), outpace mass gain from increased snow accumulation on the continent ( ''very high confidence'' ). However, there is only ''limited evidence'' , with ''medium agreement'' , of anthropogenic forcing of the observed Antarctic mass loss since 1992 (with ''low confidence'' in process attribution). Increasing mass loss from ice shelves and inland discharge will ''likely'' continue to outpace increasing snowfall over the 21st century (Figure TS.11f). Deep uncertainty persists with respect to the possible evolution of the Antarctic Ice Sheet along high-end mass-loss storylines within the 21st century and beyond, primarily related to the abrupt and widespread onset of marine ice sheet instability and marine ice cliff instability. (See also Boxes TS.3 and TS.4). Links to chapters 2.3.2, 3.4.3, 9.4.2, 9.6.3, Box 9.4, Atlas.11.1

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'''Box TS.4 | Sea Level'''

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'''Global mean sea level (GMSL) increased by 0.20 [0.15 to 0.25] m over the period 1901 to 2018, with a rate of rise that has accelerated since the 1960s to 3.7 [3.2 to 4.2] mm yr <sup>–1</sup> for the period 2006–2018 <sup></sup> ( ''high confidence'' ). Human activities were ''very likely'' the main driver of observed GMSL rise since 1971, and new observational evidence leads to an assessed sea level rise over the period 1901 to 2018 that is consistent with the sum of individual components contributing to sea level rise, including expansion due to ocean warming and melting of glaciers and ice sheets ( ''high confidence'' ). It is ''virtually certain'' that GMSL will continue to rise over the 21st century in response to continued warming of the climate system (Box TS.4, Figure 1). Sea level responds to greenhouse gas (GHG) emissions more slowly than global surface temperature, leading to weaker scenario dependence over the 21st century than for global surface temperature ( ''high confidence'' ). This slow response also leads to long-term committed sea level rise, associated with ongoing ocean heat uptake and the slow adjustment of the ice sheets, that will continue over the centuries and millennia following cessation of emissions ( ''high confidence'' ) (Box TS.9). By 2100, GMSL is projected to rise by 0.28–0.55 m ( ''likely'' range) under SSP1-1.9 and 0.63–1.01 m ( ''likely'' range) under SSP5-8.5 relative to the 1995–2014 average ( ''medium confidence'' ). Under the higher CO <sub>2</sub> emissions scenarios, there is deep uncertainty in sea level projections for 2100 and beyond associated with the ice-sheet responses to warming. In a low-likelihood, high-impact storyline and a high CO <sub>2</sub> emissions scenario, ice-sheet processes characterized by deep uncertainty could drive GMSL rise up to about 5 m by 2150. Given the long-term commitment, uncertainty in the timing of reaching different GMSL rise levels is an important consideration for adaptation planning. Links to chapters 2.3, 3.4, 3.5, 9.6, Box 9.4, Cross-Chapter Box 9.1, Table 9.5'''
GMSL change is driven by warming or cooling of the ocean (and the associated expansion/contraction) and changes in the amount of ice and water stored on land. Paleo-evidence shows that GMSL has been about 70 m higher and 130 m lower than present within the past 55 million years and was ''likely'' 5 to 10 m higher during the Last Interglacial (Box TS.2, Figure 1). Sea level observations show that GMSL rose by 0.20 [0.15 to 0.25] m over the period 1901–2018 at an average rate of 1.7 [1.3 to 2.2] mm yr <sup>–1</sup> . New analyses and paleo-evidence since AR5 show this rate is ''very likely'' faster than during any century over at least the last three millennia ( ''high confidence'' ). Since AR5, there is strengthened evidence for an increase in the rate of GMSL rise since the mid-20th century, with an average rate of 2.3 [1.6–3.1] mm yr <sup>–1</sup> over the period 1971–2018 increasing to 3.7 [3.2–4.2] mm yr <sup>–1</sup> for the period 2006–2018 ( ''high confidence'' ). Links to chapters 2.3.3, 9.6.1, 9.6.2

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'''Box TS.4, Figure 1 |'''

'''Global mean sea level (GMSL) change on different time scales and under different scenarios.''' ''The intent of this figure is to (i) show the century-scale GMSL projections in the context of the 20th century observations, (ii) illustrate ‘deep uncertainty’ in projections by considering the timing of GMSL rise milestones, and (iii) show the long-term commitment associated with different warming levels, including the paleo evidence to support this.'' '''(a)''' GMSL change from 1900 to 2150, observed (1900–2018) and projected under the SSP scenarios (2000–2150), relative to a 1995–2014 baseline. Solid lines show median projections. Shaded regions show ''likely'' ranges for SSP1-2.6 and SSP3-7.0. Dotted and dashed lines show respectively the 83rd and 95th percentile ''low confidence'' projections for SSP5-8.5. Bars at right show ''likely'' ranges for SSP1-1.9, SSP1-2.6, SSP2-4.5, SSP3-7.0 and SSP5-8.5 in 2150. Lightly shaded thick/thin bars show 17th–83rd/5th–95th percentile ''low-confidence'' ranges in 2150 for SSP1-2.6 and SSP5-8.5, based upon projection methods incorporating structured expert judgement and marine ice cliff instability. ''Low confidence'' range for SSP5-8.5 in 2150 extends to 4.8/5.4 m at the 83rd/95th percentile. '''(b)''' GMSL change on 100- (blue), 2000- (green) and 10,000-year (magenta) time scales as a function of global surface temperature, relative to 1850–1900. For 100-year projections, GMSL is projected for the year 2100, relative to a 1995–2014 baseline, and temperature anomalies are average values over 2081–2100. For longer-term commitments, warming is indexed by peak warming above 1850–1900 reached after cessation of emissions. Shaded regions show paleo-constraints on global surface temperature and GMSL for the Last Interglacial and mid-Pliocene Warm Period. Lightly shaded thick/thin blue bars show 17th–83rd/5th–95th percentile ''low confidence'' ranges for SSP1-2.6 and SSP5-8.5 in 2100, plotted at 2°C and 5°C. '''(c)''' Timing of exceedance of GMSL thresholds of 0.5, 1.0, 1.5 and 2.0 m, under different SSPs. Lightly shaded thick/thin bars show 17th–83rd/5th–95th percentile ''low-confidence'' ranges for SSP1-2.6 and SSP5-8.5. Links to chapters 4.3.2, 9.6.1, 9.6.2, 9.6.3, Box 9.4
GMSL will continue to rise throughout the 21st century (Box TS.4, Figure 1a). Considering only those processes in whose projections we have at least ''medium confidence'' , relative to the period 1995–2014, GMSL is projected to rise between 0.18 m (0.15–0.23 m, ''likely range'' ; SSP1-1.9) and 0.23 m (0.20–0.30 m, ''likely range'' ; SSP5-8.5) by 2050. By 2100, the projected rise is between 0.38 m (0.28–0.55 m, ''likely range'' ; SSP1-1.9) and 0.77 m (0.63–1.01 m, ''likely range'' ; SSP5-8.5) Links to chapters Table 9.9 . The methods, models and scenarios used for sea level projections in the AR6 are updated from those employed by SROCC, with contributions informed by the latest model projections described in the ocean and cryosphere Sections (Sections TS.2.4 and TS.2.5). Despite these differences, the sea level projections are broadly consistent with those of SROCC. Links to chapters 4.3.2, 9.6.3

Importantly, ''likely'' range projections do not include those ice-sheet-related processes whose quantification is highly uncertain or that are characterized by deep uncertainty. Higher amounts of GMSL rise before 2100 could be caused by earlier-than-projected disintegration of marine ice shelves, the abrupt, widespread onset of marine ice sheet instability (MISI) and marine ice cliff instability (MICI) around Antarctica, and faster-than-projected changes in the surface mass balance and dynamical ice loss from Greenland (Box TS.4, Figure 1). In a low-likelihood, high-impact storyline and a high CO <sub>2</sub> emissions scenario, such processes could in combination contribute more than one additional meter of sea level rise by 2100 (Box TS.3). Links to chapters 4.3.2, 9.6.3, Box 9.4

Beyond 2100, GMSL will continue to rise for centuries to millennia due to continuing deep ocean heat uptake and mass loss from ice sheets, and will remain elevated for thousands of years ( ''high confidence'' ). By 2150, considering only those processes in whose projections we have at least ''medium confidence'' and assuming no acceleration in ice-mass flux after 2100, GMSL is projected to rise between 0.6 m (0.4–0.9 m, ''likely'' range, SSP1-1.9) and 1.3 m (1.0–1.9 m, ''likely'' range) (SSP5-8.5), relative to the period 1995–2014 based on the SSP scenario extensions. Under high CO <sub>2</sub> emissions, processes in which there is ''low confidence'' , such as MICI, could drive GMSL rise up to about 5 m by 2150 (Box TS.4, Figure 1a). By 2300, GMSL will rise 0.3–3.1 m under low CO <sub>2</sub> emissions (SSP1-2.6) ( ''low confidence'' ). Under high CO <sub>2</sub> emissions (SSP5-8.5), projected GMSL rise is between 1.7 and 6.8 m by 2300 in the absence of MICI and by up to 16 m considering MICI ( ''low confidence'' ). Over 2000 years, there is ''medium agreemen'' t and ''limited evidence'' that committed GMSL rise is projected to be about 2–3 m with 1.5°C peak warming, 2–6 m with 2°C of peak warming, 4–10 m with 3°C of peak warming, 12–16 m with 4°C of peak warming, and 19–22 m with 5°C of peak warming. Links to chapters 9.6.3

Looking at uncertainty in time provides an alternative perspective on uncertainty in future sea level rise (Box TS.4, Figure 1c). For example, considering only ''medium confidence'' processes, GMSL rise is likely to exceed 0.5 m between about 2080 and 2170 under SSP1-2.6 and between about 2070 and 2090 under SSP5-8.5. Given the long-term commitment, uncertainty in the timing of reaching different levels of GMSL rise is an important consideration for adaptation planning. Links to chapters 9.6.3

At regional scales, additional processes come into play that modify the local sea level change relative to GMSL, including vertical land motion, ocean circulation and density changes, and gravitational, rotational, and deformational effects arising from the redistribution of water and ice mass between land and the ocean. These processes give rise to a spatial pattern that tends to increase sea level rise at the low latitudes and reduce sea level rise at high latitudes. However, over the 21st century, the majority of coastal locations have a median projected regional sea level rise within ±20% of the projected GMSL change ( ''medium confidence'' ). Further details on regional sea level change and extremes are provided in Section TS.4. Links to chapters 9.6.3

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'''Box TS.5 | The Carbon Cycle'''

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'''The continued growthof atmospheric CO <sub>2</sub> concentrations over the industrial era is unequivocally due to emissions from human activities. Ocean and land carbon sinks slow the rise of CO <sub>2</sub> in the atmosphere. Projections show that while land and ocean sinks absorb more CO <sub>2</sub> under high emissions scenarios than low emissions scenarios, the fraction of emissions removed from the atmosphere by natural sinks decreases with higher concentrations ( ''high confidence'' ). Projected ocean and land sinks show similar responses for a given scenario, but the land sink has a much higher interannual variability and wider model spread. The slowed growth rates of the carbon sinks projected for the second half of this century are linked to strengthening carbon–climate feedbacks and stabilization of atmospheric CO <sub>2</sub> under medium-to-no-mitigation and high-mitigation scenarios, respectively (see FAQ 5.1). Links to chapters 5.2, 5.4'''
Carbon sinks for anthropogenic CO <sub>2</sub> are associated with mainly physical ocean and biospheric land processes that drive the exchange of carbon between multiple land, ocean and atmospheric reservoirs. These exchanges are driven by increasing atmospheric CO <sub>2</sub> , but are modulated by changes in climate (Box TS.5, Figure 1c,d). The Northern and Southern Hemispheres dominate the land and ocean sinks, respectively (Box TS.5, Figure 1). Ocean circulation and thermodynamic processes also play a critical role in coupling the global carbon and energy (heat) cycles. There is ''high confidence'' that this ocean carbon–heat nexus is an important basis for one of the most important carbon–climate metrics, the transient climate response to cumulative CO <sub>2</sub> emissions (TCRE; Section TS.3.2.1) used to determine the remaining carbon budget. Links to chapters 5.1, 5.2, 5.5, 9.2, Cross-Chapter Box 5.3

Based on multiple lines of evidence using interhemispheric gradients of CO <sub>2</sub> concentrations, isotopes, and inventory data, it is unequivocal that the growth in CO <sub>2</sub> in the atmosphere since 1750 (see Section TS.2.2) is due to the direct emissions from human activities. The combustion of fossil fuels and land-use change for the period 1750–2019 resulted in the release of 700 ± 75 PgC ( ''likely'' range, 1 PgC = 10 <sup>15</sup> g of carbon) to the atmosphere, of which about 41% ± 11% remains in the atmosphere today ( ''high confidence'' ). Of the total anthropogenic CO <sub>2</sub> emissions, the combustion of fossil fuels was responsible for about 64% ± 15%, growing to an 86% ± 14% contribution over the past 10 years. The remainder resulted from land-use change. During the last decade (2010–2019), average annual anthropogenic CO <sub>2</sub> emissions reached the highest levels in human history at 10.9 ± 0.9 PgC yr <sup>–1</sup> ( ''high confidence'' ). Of these emissions, 46% accumulated in the atmosphere (5.1 ± 0.02 PgC yr <sup>–1</sup> ), 23% (2.5 ± 0.6 PgC yr <sup>–1</sup> ) was taken up by the ocean and 31% (3.4 ± 0.9 PgC yr <sup>–1</sup> ) was removed by terrestrial ecosystems ( ''high confidence'' ). Links to chapters 5.2.1, 5.2.2, 5.2.3

The ocean ( ''high confidence'' ) and land ( ''medium confidence'' ) sinks of CO <sub>2</sub> have increased with anthropogenic emissions over the past six decades (Box TS.5, Figure 1). This coherence between emissions and the growth in ocean and land sinks has resulted in the airborne fraction of anthropogenic CO <sub>2</sub> remaining at 44 ± 10% over the past 60 years ( ''high confidence'' ). Interannual and decadal variability of the ocean and land sinks indicate that they are sensitive to changes in the growth rate of emissions as well as climate variability and are therefore also sensitive to climate change ( ''high confidence'' ). Links to chapters 5.2.1

The land CO <sub>2</sub> sink is driven by carbon uptake by vegetation, with large interannual variability, for example, linked to the El Niño–Southern Oscillation (ENSO). Since the 1980s, carbon fertilization from rising atmospheric CO <sub>2</sub> has increased the strength of the net land CO <sub>2</sub> sink ( ''medium confidence'' ). During the historical period, the growth of the ocean sink has been primarily determined by the growth rate of atmospheric CO <sub>2</sub> . However, there is ''medium confidence'' that changes to physical and chemical processes in the ocean and in the land biosphere, which govern carbon feedbacks, are already modifying the characteristics of variability, particularly the seasonal cycle of CO <sub>2</sub> , in both the ocean and land. However, changes to the multi-decadal trends in the sinks have not yet been observed. Links to chapters 2.3.4, 3.6.1, 5.2.1

In AR6, ESM projections are assessedwith CO <sub>2</sub> concentrations by 2100 from about 400 ppm (SSP1-1.9) to above 1100 ppm (SSP5-8.5). Most simulations are performed with prescribed atmospheric CO <sub>2</sub> concentrations, which already account for a central estimate of climate–carbon feedback effects. Carbon dioxide emissions-driven simulations account for uncertainty in these feedbacks, but do not significantly change the projected global surface temperature changes ( ''high confidence'' ). Although land and ocean sinks absorb more CO <sub>2</sub> under high emissions than low emissions scenarios, the fraction of emissions removed from the atmosphere decreases ( ''high confidence'' ). This means that the more CO <sub>2</sub> that is emitted, the less efficient the ocean and land sinks become ( ''high confidence'' ), an effect which compensates for the logarithmic relationship between CO <sub>2</sub> and its radiative forcing, which means that for each unit increase in additional atmospheric CO <sub>2</sub> the effect on global temperature decreases. (Box TS.5, Figure 1f,g). Links to chapters 4.3.1, 5.4.5, 5.5.1.2

Ocean and land sinks show similar responses for a given scenario, but the land sink has a much higher interannual variability and wider model spread. Under SSP3-7.0 and SSP5-8.5, the initial growth of both sinks in response to increasing atmospheric concentrations of CO <sub>2</sub> is subsequently limited by emerging carbon–climate feedbacks ( ''high confidence'' ) (Box TS.5, Figure 1f). Projections show that the ocean and land sinks will stop growing from the second part of the 21st century under all emissions scenarios, but with different drivers for different emissions scenarios. Under SSP3-7.0 and SSP5-8.5, the weakening growth rate of the ocean CO <sub>2</sub> sink in the second half of the century is primarily linked to the strengthening positive feedback from reduced carbonate buffering capacity, ocean warming and altered ocean circulation (e.g., AMOC changes). In contrast, for SSP1-1.9, SSP1-2.6 and SSP2-4.5, the weakening growth rate of the ocean carbon sink is a response to the stabilizing or declining atmospheric CO <sub>2</sub> concentrations. Under SSP1-1.9, models project that combined land and ocean sinks will turn into a weak source by 2100 ( ''medium confidence'' ). Under high CO <sub>2</sub> emissions scenarios, it is ''very likely'' that the land carbon sink will grow more slowly due to warming and drying from the mid-21st century, but it is ''very unlikely'' that it will switch from being a sink to a source before 2100.

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'''Box TS.5, Figure 1 |'''

'''Carbon cycle processes and projections.''' ''The intent of this figure is to show the response of the carbon cycle to carbon dioxide (CO'' 2 '') emissions and climate and its role in determining future CO'' 2 ''levels through projected changes to sinks and sink fractions.'' The figure shows changes in carbon storage in response to elevated CO <sub>2</sub> '''(a, b)''' and the response to climate warming '''(c, d)''' . Maps show spatial patterns of changes in carbon uptake during simulations with 1% per year increase in CO <sub>2</sub> ( [[IPCC:Wg1:Chapter:Chapter-5#5.4.5.5|Section 5.4.5.5]] ), and zonal mean plots show distribution of carbon changes is dominated by the land (green lines) in the tropics and Northern Hemisphere and ocean (blue lines) in the Southern Hemisphere. Hatching indicates regions where fewer than 80% of models agree on the sign of response. '''(e)''' Future CO <sub>2</sub> projections: projected CO <sub>2</sub> concentrations in the Shared Socio-economic Pathway (SSP) scenarios in response to anthropogenic emissions, results from coupled Earth system models for SSP5-8.5 and from the MAGICC7 emulator for other scenarios ( [[IPCC:Wg1:Chapter:Chapter-4#4.3.1|Section 4.3.1]] ). '''(f)''' Future carbon fluxes: projected combined land and ocean fluxes (positive downward) up to 2100 for the SSP scenarios, and extended to 2300 for available scenarios, 5–95% uncertainty plumes shown for SSP1-2.6 and SSP3-7.0 (Sections 4.3.2.4, 5.4.5.4 and 5.4.10). The numbers near the top show the number of model simulations used. '''(g)''' Sink fraction: the fraction of cumulative emissions of CO <sub>2</sub> removed by land and ocean sinks. The sink fraction is smaller under conditions of higher emissions. Links to chapters Figure 4.3; 5.4.5; Figures 5.25, 5.27 and 5.30
Climate change alone is expected to increase land carbon accumulation in the high latitudes (not including permafrost, which is assessed in Sections TS.2.5 and TS.3.2.2), but also to lead to a counteracting loss of land carbon in the tropics ( ''medium confidence'' ). Earth system model projections show that the overall uncertainty of atmospheric CO <sub>2</sub> by 2100 is still dominated by the emissions pathway, but carbon–climate feedbacks (see Section TS.3.3.2) are important, with increasing uncertainties in high emissions pathways (Box TS.5, Figure 1e). Links to chapters 4.3.2, 5.4.1, 5.4.2, 5.4.4, 5.4.5, 11.6, 11.9, Cross-Chapter Box 5.1, Cross-Chapter Box 5.3

Under three SSP scenarios with long-term extensions until 2300 (SSP5-8.5, SSP5-3.4-OS, SSP1-2.6), ESMs project a change of the land from a sink to a source ( ''medium confidence'' ). The scenarios make simplified assumptions about emissions reductions, with SSP1-2.6 and SSP5-3.4-OS reaching about 400 ppm by 2300, while SSP5-8.5 exceeds 2000 ppm. Under high emissions, the transition is warming-driven, whereas it is linked to the decline in atmospheric CO <sub>2</sub> under net negative CO <sub>2</sub> emissions. The ocean remains a sink throughout the period to 2300 except under very large net negative emissions. The response of the natural aspects of the carbon cycle to carbon dioxide removal is further developed in Section TS.3.3.2. Links to chapters 5.4.9

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