Editing IPCC:AR6/WGI/Chapter-1 (section)

==== 1.2.2.6 The Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) ====

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Efforts to address climate change take place alongside and in the context of other major environmental problems, such as biodiversity loss. IPBES, established in 2012, builds on the IPCC model of a science–policy interface and assessment. The Platform’s objective is to ‘strengthen the science–policy interface for biodiversity and ecosystem services for the conservation and sustainable use of biodiversity, long-term human well-being and sustainable development’ ( [[#UNEP--2012|UNEP, 2012]] ). The SROCC ( [[#IPCC--2019b|IPCC, 2019b]] ) and SRCCL ( [[#IPCC--2019a|IPCC, 2019a]] ) assessed the relations between changes in biodiversity and in the climate system. The rolling work programme of IPBES up to 2030 will address interlinkages among biodiversity, water, food and health. This assessment will use a nexus approach to examine interlinkages between biodiversity and the above-mentioned issues, including climate change mitigation and adaptation. Furthermore, IPBES and IPCC will directly collaborate on biodiversity and climate change under the rolling work programme.

Addressing climate change alongside other environmental problems, while simultaneously supporting sustainable socio-economic development, requires a holistic approach. Since AR5, there is increasing attention on the need for coordination among previously independent international agendas, and a recognition that climate change, disaster risk, economic development, biodiversity conservation and human well-being are tightly interconnected. The current COVID-19 pandemic provides an example of the need for such interconnection, with its widespread impacts on economy, society and environment (e.g., [[#Shan--2021|Shan et al., 2021]] ). Cross-Chapter Box 6.1 assesses the consequences of the COVID-19 lockdowns for emissions of GHGs and SLCFs, and related implications for the climate. Another example of the interconnected nature of these issues is the close link between SLCF emissions, climate change and air quality concerns (Chapter 6). Emissions of halocarbons have previously been successfully regulated under the Montreal Protocol and its Kigali Amendment. This has been achieved in an effort to reduce ozone depletion that has also modulated other anthropogenic climate influence ( [[#Estrada--2013|Estrada et al., 2013]] ; [[#Wu--2013|Wu et al., 2013]] ). In the process, emissions of some SLCFs were jointly regulated to reduce environmental and health impacts from air pollution (e.g., Gothenburg Protocol; [[#Reis--2012|Reis et al., 2012]] ). Considering the recognized importance of SLCFs in climate change processes, the IPCC decided in May 2019 to approve that the IPCC Task Force on National Greenhouse Gas Inventories produces an IPCC Methodology Report on SLCFs to develop guidance for national SLCF inventories.

The evolving governance context since AR5 challenges the IPCC to provide policymakers and other actors with information relevant for both adaptation to and mitigation of climate change, and for the loss and damage induced.

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'''Cross-Chapter Box 1.1 | The WGI Contribution to AR6 and Its Potential Relevance for the Global Stocktake'''

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'''Contributing Authors:''' Malte Meinshausen (Australia/Germany), Gian-Kasper Plattner (Switzerland), Aïda Diongue-Niang (Senegal), Francisco J. Doblas-Reyes (Spain), David Frame (New Zealand), Nathan P. Gillett (Canada), Helene T. Hewitt (United Kingdom), Richard G. Jones (United Kingdom), Hong Liao (China), Jochem Marotzke (Germany), James Renwick (New Zealand), Joeri Rogelj (United Kingdom, Belgium), Maisa Rojas (Chile), Sonia I. Seneviratne (Switzerland), Claudia Tebaldi (United States of America), Blair Trewin (Australia)

'''The global stocktake under the Paris Agreement (PA) evaluates the collective progress of countries’ actions towards attaining the Agreement’s purpose and long-term goals every five years.''' The first global stocktake is due in 2023, and then every five years thereafter, unless otherwise decided by the Conference of the Parties. The purpose and long-term goals of the PA are captured inter alia in Article 2: to ‘strengthen the global response to the threat of climate change, in the context of sustainable development and efforts to eradicate poverty, including by’: ''mitigation'' ''[[#footnote-005|3]]'' specifically, ‘holding the increase in the global average temperature to well below 2°C above pre-industrial levels and to pursue efforts to limit the temperature increase to 1.5°C above pre-industrial levels, recognizing that this would significantly reduce the risks and impacts of climate change’; ''adaptation'' , that is, ‘increasing the ability to adapt to the adverse impacts of climate change and foster climate resilience and low greenhouse gas (GHG) emissions development, in a manner that does not threaten food production’; and ''means of implementation and support'' , that is, ‘making finance flows consistent with a pathway towards low GHG emissions and climate-resilient development.’

The PA further specifies that the stocktake shall be undertaken in a ‘comprehensive and facilitative manner, considering mitigation, adaptation and the means of implementation and support, and in the light of equity and the best available science’ (Article 14). '''The sources of input''' envisaged for the global stocktake include the ‘latest reports of the Intergovernmental Panel on Climate Change’ as a central source of information. <sup>[[#footnote-004|4]]</sup> The global stocktake is one of the key formal avenues for scientific inputs into the UNFCCC and PA negotiation process alongside, for example, the Structured Expert Dialogues (SEDs) under the UNFCCC ( [[#1.2.2|Section 1.2.2]] ). <sup>[[#footnote-003|5]]</sup>

'''The WGI Assessment provides a wide range of information with potential relevance for the global stocktake, complementing the IPCC AR6 Special Reports, the contributions from WGII and WGIII and the Synthesis Report.''' This includes the state of GHG emissions and concentrations, the current state of the climate, projected long-term warming levels under different scenarios, near-term projections, the attribution of extreme events, and remaining carbon budgets. Cross-Chapter Box 1.1, Table 1 provides pointers to the in-depth material that WGI has assessed and that may be relevant for the global stocktake.

'''The following tabular overview of potentially relevant information from the WGI contribution for the global stocktake is structured into three sections: the current state of the climate, the long-term future, and the near-term.''' These sections and their order align with the three questions of the Talanoa dialogue, launched during COP23, based on the Pacific concept of ''talanoa'' ''[[#footnote-002|6]]'' : ‘ ''Where are we’, ‘Where do we want to go’'' and ‘ ''How do'' ''we get there?’''

'''Cross-Chapter Box 1.1, Table 1 |'''

'''WGI assessment findings and their potential relevance for the global stocktake.''' The table combines information assessed in this report that could potentially be relevant for the global stocktake process. Section 1 focuses on the current state of the climate and its recent past. Section 2 focuses on long-term projections in the context of the PA’s 1.5°C and 2.0°C goals and on progress towards net zero greenhouse gas emissions. Section 3 considers challenges and key insights for mitigation and adaptation in the near term from a WGI perspective. Further information on potential relevance of the aspects listed here in terms of, for example, impacts and socio-economic aspects can be found in the WGII and WGIII reports
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! colspan="3"| '''Section 1: State of the Climate –''' ‘ ''Where are we?’''

''WGI Assessment to inform about past changes in the climate system, current climate and co'' ''mmitted changes''

|-
! '''Question'''

! '''Chapter/Section'''

! '''Potential Relevance and Expl''' '''anatory Remarks'''

|-
| How much warming have we observed in global mean surface air temperatures?

| Cross-Chapter Box 1.2; Cross-Chapter Box 2.3;

2.3.1.1, especially 2.3.1.1.3

| Knowledge about the current warming relative to pre-industrial levels allows us to quantify the remaining distance to the PA goal of keeping global mean temperatures well below 2°C above pre-industrial levels or pursue best efforts to limit warming to 1.5°C above pre-industrial levels. Many of the Report’s findings are provided against a proxy for pre-industrial temperature levels, with Cross-Chapter Box 1.2 examining the difference between pre-industrial levels and the 1850–1900 period.

|-
| How much has the ocean warmed?

| 2.3.3.1; 7.2; Box 7.2; 9.2.1.1; Box 9.1

| A warming ocean can affect marine life (e.g., coral bleaching) and is also one of the main contributors to long-term sea level rise (thermal expansion). Marine heatwaves can accentuate the impacts of ocean warming on marine ecosystems. Also, knowing the heat uptake of the ocean helps to better understand the response of the climate system and hence helps to project future warming.

|-
| How much have land areas warmed and how has precipitation changed?

| 2.3.4; 5.4.3; 5.4.8; 8.2.1; 8.2.3; 8.5.1

| A stronger than global-average warming over land, combined with changing precipitation patterns, and/or increased aridity in some regions (like the Mediterranean) can severely affect land ecosystems and species distributions, the terrestrial carbon cycle, and food production systems. Amplified warming in the Arctic can enhance permafrost thawing, which in turn can result in overall stronger anthropogenic warming (a positive feedback loop). Intensification of heavy precipitation events can cause more severe impacts related to flooding.

|-
| How did the sea ice area change in recent decades in both the Arctic and Antarctic?

| 2.3.2.1.1; 2.3.2.1.2;

9.3; Cross-Chapter Box 10.1; 12.4.9

| Sea ice area influences mass and energy (ice albedo, heat and momentum) exchange between the atmosphere and the ocean, and its changes in turn impact polar life, adjacent land and ice masses and complex dynamical flows in the atmosphere. The loss of a year-round sea ice cover in the Arctic can severely impact Arctic ecosystems, affect the livelihood of First Nations in the Arctic, and amplify Arctic warming with potential consequences for the warming of the surrounding permafrost regions and ice sheets.

|-
| How much have atmospheric CO <sub>2</sub> and other GHG concentrations increased?

| 2.2.3; 2.2.4; 5.1.1; 5.2.2; 5.2.3; 5.2.4

| The main human influence on the climate is via combustion of fossil fuels and CO <sub>2</sub> emissions related to land-use change: the principal causes of increased CO <sub>2</sub> concentrations since the pre-industrial period. Historical observations indicate that current atmospheric concentrations are unprecedented within at least the last 800 kyr. An understanding of historical fossil fuel emissions and carbon cycle interactions, as well as methane (CH <sub>4</sub> ) and nitrous oxide (N <sub>2</sub> O) sinks and sources, are crucial for better estimates of future GHG emissions compatible with the PA’s long-term goals.

|-
| How much did sea level rise in past centuries and how large is the long-term commitment?

| 2.3.3.3;

9.6.1; 9.6.2; FAQ 9.1; Box 9.1; 9.6.3; 9.6.4

| Sea level rise is a comparatively slow consequence of a warming world. Historical warming committed the world already to long-term sea level rise that is not reversed in even the lowest emissions scenarios (such as 1.5°C), which come with a commitment to a multi-metre sea level rise. Regional sea level change near coastlines differs from global mean sea level change due to vertical land movement, ice mass changes and ocean dynamical changes.

|-
| How much has the ocean acidified and how much oxygen has it lost?

| 2.3.4.3; 2.3.4.2; 5.3

| Ocean acidification is affecting marine life, especially organisms that build calciferous shells and structures (e.g., coral reefs). Together with less oxygen in upper ocean waters and increasingly widespread oxygen minimum zones, and in addition to ocean warming, this poses adaptation challenges for coastal and marine ecosystems and their services, including seafood supply.

|-
| How much of the observed warming was due to anthropogenic influences?

| 3.3.1

| To monitor progress toward the PA’s long-term goals it is important to know how much of the observed warming is due to human activities. [[IPCC:Wg1:Chapter:Chapter-3|Chapter 3]] assesses human-induced warming in global mean near-surface air temperature for the decade 2010–2019, relative to 1850–1900 with associated uncertainties, based on detection and attribution studies. This estimate can be compared with observed estimates of warming for the same decade reported in Chapter 2, and is typically used to calculate carbon budgets consistent with remaining below a particular temperature threshold.

|-
| How much has anthropogenic influence changed other aspects of the climate system?

| 3.3.2; 3.3.3; 3.4; 3.5; 3.6; 3.7; 8; 10.4; 12

| Climate change impacts are driven by changes in many aspects of the climate system, including changes in the water cycle, atmospheric circulation, ocean, cryosphere, biosphere and modes of variability. To better plan climate change adaptation it is relevant to know which observed changes have been driven by human influence.

|-
| How much are anthropogenic emissions contributing to changes in the severity and frequency of extreme events?

| 1.5; Cross-Chapter Box 1.3; Cross-Chapter Box 3.2; 9.6.4; 11.3–11.8; 12.3

| Adaptation challenges are often accentuated in the face of extreme events, including floods, droughts, bushfires and tropical cyclones. For agricultural management, infrastructure planning, and designing for climate resilience it is relevant to know whether extreme events will become more frequent in the near future. In that respect it is important to understand whether observed extreme events are part of a natural background variability or caused by past anthropogenic emissions. This attribution of extreme events is therefore key to understanding current events, as well as to better project the future evolution of these events, such as temperature extremes, heavy precipitation, floods, droughts, extreme storms and compound events, and extreme sea level. Also, loss and damage events are often related to extreme events, which means that future disasters can be fractionally attributed to past human emissions.

|}

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! colspan="3"| '''Section 2: Long-Term Climate Futures –''' ''‘Where do'' ''we want to go?’''

''WGI Assessment to inform how long-term climate change could unfold depending on chosen em'' ''issions futures''

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! '''Question'''

! '''Chapter'''

! '''Potential Relevance and Expl''' '''anatory Remarks'''

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| How are climate model projections used to project the range of future global and regional climate changes?

| 3.8.2; Cross-Chapter Box 3.1; Box 4.1; 10.3; 10.4; 12.4

| The scientific literature provides new insights in a developing field of scientific research regarding evaluating model performance and weighting. This can lead to more constrained projection ranges for a given scenario and some variables, which take into account the performance of climate models and interdependencies among them. These techniques have a strong relevance to quantifying future uncertainties, for example regarding the likelihood of the various scenarios exceeding the PA’s long-term temperature goals of 1.5°C or 2°C.

|-
| If emissions scenarios are pursued that achieve mitigation goals by 2050, what will be the difference in climate over the 21st century compared to emissions scenarios where no additional climate policies are implemented?

| 1.2.2; 4.6; FAQ 4.2; Chapters 9 and 11; 12.4; Atlas;

Interactive Atlas

| Estimating the scale and timing of mitigation compatible with the PA’s long-term goals requires an understanding of the climate system response to a change in anthropogenic emissions. The new generation of scenarios spans the response space from very low emissions scenarios (SSP1-1.9) under the assumption of accelerated and effective climate policy implementation, to very high emissions scenarios in the absence of additional climate policies (SSP3-7.0 or SSP5-8.5). It can be informative to place current NDCs and their emissions mitigation pledges within this low- and high-end scenario range, that is, in the context of intermediate-high emissions scenarios (RCP4.5, RCP6.0 or SSP4-6.0). Climate response differences between those future intermediate or high emissions scenarios and those compatible with the PA’s long-term temperature goals can help inform policymakers about the corresponding adaptation challenges.

|-
| What is the climatic effect of net zero GHG emissions and a balance between anthropogenic sources and anthropogenic sinks?

| Box 1.4; 4.7.2; 5.2.2–5.2.4; 7.6

| Understanding the long-term climate effect of global emissions levels, including the effect of net zero emissions targets adopted by countries as part of their long-term climate strategies, can be important when assessing whether the collective level of mitigation action is consistent with the long-term goals of the PA. Understanding the dynamics of natural sources of CO <sub>2</sub> , CH <sub>4</sub> and N <sub>2</sub> O is a fundamental prerequisite to derive climate projections. Net zero GHG emissions, that is, the balance between anthropogenic sources and anthropogenic sinks of CO <sub>2</sub> and other GHGs, will halt human-induced global warming and/or lead to slight reversal below peak warming levels. Net zero CO <sub>2</sub> emissions will approximately lead to a stabilization of CO <sub>2</sub> -induced global warming.

|-
| What is the remaining carbon budget that is consistent with the PA’s long-term temperature goals?

| 5.5

| The remaining carbon budget provides an estimate of how much CO <sub>2</sub> can still be emitted into the atmosphere by human activities while keeping GMST to a specific warming level. It thus provides key geophysical information about emissions limits consistent with limiting global warming to well below 2°C above pre-industrial levels and to pursue efforts to limit the temperature increase to 1.5°C. Remaining carbon budgets can be seen in the context of historical CO <sub>2</sub> emissions to date. The concept of the transient climate response to cumulative CO <sub>2</sub> emissions (TCRE) indicates that one tonne of CO <sub>2</sub> has the same effect on global warming irrespective of whether it is emitted in the past, today, or in the future. In contrast, the global warming from short-lived climate forcers (SLCFs) is dependent on their rate of emission rather than their cumulative emissions.

|-
| What is our current knowledge on the ‘Reasons for Concern’ related to the PA’s long-term temperature goals and higher warming levels?

| Cross-Chapter Box 12.1; individual domains are discussed in 2.3.3; 3.5.4; 4.3.2; 5.3; 8.4.1; 9.4.2, 9.5; Chapters 11 and 12

| Synthesis information on projected changes in indices of climatic impact-drivers feeds into different Reasons for Concern. Where possible, an explicit transfer function between different warming levels and indices quantifying characteristics of these hazards is provided, or the difficulties in doing so documented. Those indices include Arctic sea ice area in September; global average change in ocean acidification; volume of glaciers or snow cover; ice volume change for the West Antarctic Ice Sheet (WAIS) and Greenland Ice Sheet (GrIS); Atlantic Meridional Overturning Circulation (AMOC) strength; amplitude and variance of El Niño–Southern Oscillation (ENSO) mode (Niño 3.4 index); and weather and climate extremes.

|-
| What are the climate effects and air pollution co-benefits of rapid decarbonisation due to the reduction of co-emitted short-lived climate forcers (SLCFs)?

| 6.6.3; 6.7.3; Box 6.2

| Understanding to what degree rapid decarbonization strategies bring about reduced air pollution due to reductions in co-emitted SLCFs can help inform considerations of integrated and/or complementary policies, with synergies for pursuing the PA goals, the World Health Organization (WHO) air quality guidelines and the Sustainable Development Goals (SDGs).

|-
| What are the equilibrium climate sensitivity (ECS), the transient climate response (TCR), and transient climate response to CO <sub>2</sub> emissions (TCRE) and what do these indicators tell us about expected warming over the 21st century under various scenarios?

| Box 4.1; 5.4; 5.5.1; 7.5

| ECS measures the long-term global mean warming in response to doubling CO <sub>2</sub> concentrations from pre-industrial levels, while TCR also takes into account the inertia of the climate system and is an indicator for the near- and medium-term warming. TCRE is similar to TCR, but asks the question of what is the implied warming in response to cumulative CO <sub>2</sub> emissions (rather than CO <sub>2</sub> concentration changes). The higher the ECS, TCR or TCRE, the lower are the GHG emissions that are consistent with the PA’s long-term temperature goals.

|-
| What is the Earth’s energy imbalance and why does it matter?

| 7.2.2

| The current global energy imbalance implies that one can expect additional warming before the Earth’s climate system attains equilibrium with the current level of concentrations and radiative forcing. Note though, that future warming commitments can be different depending on how future concentrations and radiative forcing change.

|-
| What are the regional and long-term changes in precipitation, evaporation and runoff?

| 8.4.1; 8.5; 8.6; 10.4; 10.6; 11.4; 11.9; 11.6; 11.7; 12.4; Atlas; Interactive Atlas

| Changes in regional precipitation – in terms of both extremes and long-term averages – are important for estimating adaptation challenges. Projected changes of precipitation minus evaporation (P–E) are closely related to surface water availability and drought probability. Understanding water cycle changes over land, including seasonality, variability and extremes, and their uncertainties, is important to estimate a broad range of climate impacts and adaptation, including food production, water supply and ecosystem functioning.

|-
| Are we committed to irreversible sea level rise and what is the expected sea level rise by the end of the century if we pursue strong mitigation or high emissions scenarios?

| 4.7.2; 9.6.3; 9.6.4; 12.4;

Interactive Atlas

| Unlike many regional climate responses, global mean sea level (GMSL) keeps rising, even in the lowest emissions scenarios and is not halted when warming is halted. This is due to the long time scales on which ocean heat uptake, glacier melt and ice sheets react to temperature changes. Tipping points and thresholds in polar ice sheets need to be considered. Thus, sea level rise commitments and centennial-scale irreversibility of ocean warming and sea level rise are important for future impacts under even the lowest of the emissions scenarios.

|-
| Can we project future climate extremes under various global warming levels in the long term?

| Chapter 11; 12.4;

Interactive Atlas

| Projections of future extreme weather and climate events and their regional occurrence, including at different global warming levels, are important for adaptation and disaster risk reduction. The attribution of these extreme events to natural variability and human-induced changes can be of relevance for both assessing adaptation challenges and issues of loss and damage.

|-
| What is the current knowledge of potential surprises, abrupt changes, tipping points and low-likelihood, high-impact outcomes related to different levels of future emissions or warming?

| 1.4.4; 4.7.2; 4.8; 5.4.8; Box 5.1; 8.5.3.2; 8.6.2; Box 9.4; 11.2.4; Cross-Chapter Box 4.1; Cross-Chapter Box 12.1

| From a risk perspective, it is useful to have information about lower-probability events and system changes, if they have the potential to result in high impacts, given the dynamic interactions between climate-related hazards and socio-economic drivers (i.e., exposure and vulnerability of the affected human or ecological systems). Examples include permafrost thaw, CH <sub>4</sub> clathrate feedbacks, ice-sheet mass loss and ocean turnover circulation changes, all of which can accelerate warming globally or yield particular regional responses and impacts.

|}

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! colspan="3"| '''Section 3: The Near Term –''' ‘ ''How do'' ''we get there?’''

''WGI Assessment to inform near-term adaptation and mit'' ''igation options''

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! '''Questions'''

! '''Chapter'''

! '''Potential Relevance and Expl''' '''anatory Remarks'''

|-
| What are projected key climate indices under low, intermediate and high emissions scenarios in the near term, that is, the next 20 years?

| 4.3; 4.4; FAQ 4.1, 10.6; 12.3; Atlas; Interactive Atlas

| Much of the near-term information and comparison to historical observations allows us to quantify the climate adaptation challenges for the next decades as well as the opportunities to reduce climate change by pursuing lower emissions. For this time scale both the forced changes and the internal variability are important.

|-
| How can the climate benefit of mitigating emissions of different GHGs be compared?

| 7.6

| For mitigation challenges, it is important to compare efforts to reduce emissions of CO <sub>2</sub> versus emissions of other climate forcers, such as short-lived CH <sub>4</sub> or long-lived N <sub>2</sub> O. Global warming potentials (GWPs), which are used in the UNFCCC and in emissions inventories, are updated and various other metrics are also investigated in this Report. While the NDCs of Parties to the PA, emissions inventories under the UNFCCC, and various emissions trading schemes work on the basis of GWP-weighted emissions, some recent discussion in the scientific literature also considers projecting temperatures induced by SLCFs on the basis of emissions changes, not emissions per se.

|-
| Do mountain glaciers shrink, currently and in the near future, in regions that are currently dependent on them for seasonal freshwater supply?

| 2.3.2.3; 8.4.1;

9.5; Cross-Chapter Box 10.4; 12.4:

Atlas.5.2.2;

Atlas.5.3.2;

Atlas.6.2; Atlas.9.2

| Mountain glaciers and seasonal snow cover often feed downstream river systems during the melting period, and can be an important source of freshwater. Changing river discharge can pose adaptation challenges. Melting mountain glaciers are among the main contributors to observed GMSL rise.

|-
| What are the capacities and limitations in the provision of regional climate information for adaptation and risk management?

| Cross-Chapter Box 1.3; 10.5; 10.6; Box 10.2; Cross-Chapter Box 10.4; 11.9; 12.6; Cross-Chapter Box 12.1

| Challenges for adaptation and risk management are predominantly local, even if globally interlinked. There are a number of approaches used in the production of regional climate information for adaptation purposes focusing on regional scales. All of them consider a range of sources of data and knowledge that are distilled into, at times contextual, climate information. A wealth of examples can be found in this Report, including assessments of extremes and climatic impact-drivers, and attribution at regional scales. Specific regions and case studies for regional projections are considered, like the Sahel and West African monsoon drought and recovery, the southern Australian rainfall decline, and the Caribbean small island summer drought, and regional projections are discussed for Cape Town, the Mediterranean region and Hindu Kush Himalaya.

|-
| How important are reductions in short-lived climate forcers compared to the reduction of CO <sub>2</sub> and other long-lived GHGs?

| 6.1; 6.6; 6.7; 7.6

| While most of the radiative forcing which causes climate change comes from CO <sub>2</sub> emissions, short-lived climate forcers also play an important role in the anthropogenic effect on climate change. Many aerosol species, especially SO4, tend to cool the climate and mask some GHG-induced warming, so reductions in these SLCFs would have a warming effect. On the other hand, many short-lived species themselves exert a warming effect, including black carbon and CH <sub>4</sub> , the second most important anthropogenic GHG (in terms of current radiative forcing). Notably, the climate response to aerosol emissions has a strong regional pattern and is different from that of GHG-driven warming.

|-
| What are potential co-benefits and side effects of climate change mitigation?

| 5.6.2; 6.1; 6.7.5

| The reduction of fossil fuel-related emissions often goes hand-in-hand with a reduction of air pollutants, such as aerosols and ozone. Reductions will improve air quality and result in broader environmental benefits (reduced acidification, eutrophication, and often tropospheric ozone recovery). More broadly, various co-benefits are discussed in WGII and WGIII, as well as co-benefits and side effects related to certain mitigation actions, like increased biomass use and associated challenges to food security and biodiversity conservation.

|-
| What large near-term surprises could result in particular adaptation challenges?

| 1.4; 4.4.4; Cross-Chapter Box 4.1; 8.5.2; 11.2.4; Cross-Chapter Box 12.1

| Surprises can come from a range of sources: from incomplete understanding of the climate system, from surprises in emissions of natural (e.g., volcanic) sources, or from disruptions to the carbon cycle associated with a warming climate (e.g., methane release from permafrost thawing, tropical forest dieback). There could be large natural variability in the near term; or also accelerated climate change due to a markedly more sensitive climate than previously thought. When the next large explosive volcanic eruption will happen is unknown. The largest volcanic eruptions over the last few hundred years led to substantial but temporary cooling, including precipitation changes.

|}

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