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

== 1.1 Why this Special Report? ==

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All people depend directly or indirectly on the ocean and cryosphere (see FAQ1.1). Coasts are the most densely populated areas on Earth. As of 2010, 28% of the global population (1.9 billion people) were living in areas less than 100 km from the coastline and less than 100 m above sea level, including 17 major cities which are each home to more than 5 million people (Kummu et al., 2016 <sup>[[#fn:r1|1]]</sup> ). Small Island Developing States are together home to around 65 million people (UN, 2015a). The low elevation coastal zone (land less than 10 m above sea level), where people and infrastructure are most exposed to coastal hazards, is currently home to around 11% of the global population (around 680 million people), and by 2050 the population in this zone is projected to grow to more than one billion under all Shared Socioeconomic Pathways (SSPs) (Section 4.3.3.2; Merkens et al., 2016 <sup>[[#fn:r2|2]]</sup> ; O’Neill et al., 2017 <sup>[[#fn:r3|3]]</sup> ). In 2010, approximately 4 million people lived in the Arctic (Section 3.5.1), and an increase of only 4% is projected for 2030 (Heleniak, 2014 <sup>[[#fn:r4|4]]</sup> ) compared to 16 – 23% for the global population increase (O’Neill et al., 2017 <sup>[[#fn:r5|5]]</sup> ). Almost 10% of the global population (around 670 million people) lived in high mountain regions in 2010, and by 2050 the population in these regions is expected to grow to between 736 – 844 million across the SSPs (Section 2.1). For people living in close contact with the ocean and cryosphere, these systems provide essential livelihoods, food security, well-being and cultural identity, but are also a source of hazards (Sections 1.5.1, 1.5.2).

Even people living far from the ocean or cryosphere depend on these systems. Snow and glacier melt from high mountains helps to sustain the rivers that deliver water resources to downstream populations (Kaser et al., 2010 <sup>[[#fn:r6|6]]</sup> ; Sharma et al., 2019 <sup>[[#fn:r7|7]]</sup> ). In the Indus and Ganges river basins, for example, snow and glacier melt provides enough water to grow food crops to sustain a balanced diet for 38 million people, and supports the livelihoods of 129 million farmers (Biemans et al., 2019 <sup>[[#fn:r8|8]]</sup> ). The ocean and cryosphere regulate global climate and weather; the ocean is the primary source of rain and snowfall needed to sustain life on land, and uptake of heat and carbon into the ocean has so far limited the magnitude of anthropogenic warming experienced at the Earth’s surface (Section 1.2). The ocean’s biosphere is responsible for about half of the primary production on Earth, and around 17% of the non-grain protein in human diets is derived from the ocean (FAO, 2018). Communities far from the coast can also be exposed to changes in the ocean through extreme weather events. Ocean and cryosphere changes can result in differing consequences and benefits on local to global scales; for example, declining sea ice in the Arctic is allowing access to shorter international shipping routes but restricting traditional sea ice based travel for Arctic communities.

Human activities are estimated to have so far caused approximately 1°C of global warming (0.8°C – 1.2°C likely range; above pre-industrial levels; IPCC, 2018 <sup>[[#fn:r9|9]]</sup> ). The IPCC Fifth Assessment Report (AR5) concluded that, ‘Warming of the climate system is unequivocal, and since the 1950s, many of the observed changes are unprecedented over decades to millennia. The atmosphere and ocean have warmed, the amounts of snow and ice have diminished, sea level has risen, and the concentrations of greenhouse gases have increased’ (IPCC, 2013 <sup>[[#fn:r10|10]]</sup> ). Subsequently, Parties to the Paris Agreement aimed to strengthen the global response to the threats of climate change, including by ‘holding the increase in global average temperature to well below 2°C above pre-industrial levels and pursuing efforts to limit the temperature increase to 1.5°C’ (UNFCCC, 2015 <sup>[[#fn:r11|11]]</sup> ).

Pervasive ocean and cryosphere changes that are already being caused by human-induced climate change are observed from high mountains, to the polar regions, to coasts and into the deep reaches of the ocean. Changes by the end of this century are expected to be larger under high greenhouse gas emission futures compared with low-emission futures (Cross-Chapter Box 1 in Chapter 1), and inaction on reducing emissions will have large economic costs. If human impacts on the ocean continue unabated, declines in ocean health and services are projected to cost the global economy 428 billion USD yr -1 by 2050, and 1.979 trillion USD yr -1 by 2100. Alternatively, steps to reduce these impacts could save more than a trillion dollars USD yr -1 by 2100 (Ackerman, 2013 <sup>[[#fn:r12|12]]</sup> ). Similarly, sea level rise scenarios of 25 to 123 cm by 2100 without adaptation are expected to see 0.2 – 4.6% of the global population impacted by coastal flooding annually, with average annual losses amounting to 0.3 – 9.3% of global GDP. Investment in adaptation reduces by 2 to 3 orders of magnitude the number of people flooded and the losses caused (Hinkel et al., 2014 <sup>[[#fn:r13|13]]</sup> ).

The United Nations 2030 SDGs (UN, 2015b) are all connected to varying extents with the ocean and cryosphere (see FAQ1.2). Climate action (SDG 13) would limit future ocean and cryosphere changes ( ''high confidence'' ; Cross-Chapter Box 1 in Chapter 1, Figure 1.5, Chapter 2 to 6), and would reduce risks to SDGs that are fundamentally linked to the ocean and cryosphere, including life below water, and clean water and sanitation. (Sections 2.4, 4.4, 5.4; Szabo et al., 2016 <sup>[[#fn:r14|14]]</sup> ; LeBlanc et al., 2017 <sup>[[#fn:r15|15]]</sup> ; Singh et al., 2018 <sup>[[#fn:r16|16]]</sup> ; Visbeck, 2018 <sup>[[#fn:r17|17]]</sup> ; Wymann von Dach et al., 2018 <sup>[[#fn:r18|18]]</sup> ; Kulonen, Accepted). Other goals for sustainable development depend on the services the ocean and cryosphere provide or are impacted by ocean and cryosphere change; including, life on land, health and wellbeing, eradicating poverty and hunger, economic growth, clean energy, infrastructure, and sustainable cities and communities. Progress on the other SDGs (education, gender equality, reduced inequalities, responsible consumption, strong institutions, and partnerships for the goals) are important for reducing the vulnerability of people and communities to the risks of ocean and cryosphere changes (Section 1.5; 2.3), and for supporting mitigation and adaptation responses (Sections 1.6, 1.7 and 1.8.3; ''medium confidence'' ).

The characteristics of ocean and cryosphere change (Section 1.3) present particular challenges to climate-resilient development pathways (CRDPs). Ocean acidification and deoxygenation, ice sheet and glacier mass loss, and permafrost degradation are expected to be irreversible on time scales relevant to human societies and ecosystems (Lenton et al., 2008 <sup>[[#fn:r19|19]]</sup> ; Solomon et al., 2009 <sup>[[#fn:r20|20]]</sup> ; Frölicher and Joos, 2010 <sup>[[#fn:r21|21]]</sup> ; Cai et al., 2016 <sup>[[#fn:r22|22]]</sup> ; Kopp et al., 2016 <sup>[[#fn:r23|23]]</sup> ). Ocean and cryosphere changes also have the potential to worsen anthropogenic climate change, globally and regionally; for example, by additional greenhouse gas emissions released through permafrost thaw that would intensify anthropogenic climate change globally, or by increasing the absorption of solar radiation through snow and ice loss in the Arctic that is causing regional climate to warm at more than twice the global rate (AMAP, 2017 <sup>[[#fn:r24|24]]</sup> ; Steffen et al., 2018 <sup>[[#fn:r25|25]]</sup> ). Ocean and cryosphere changes place particular pressures on the adaptive capacities of cultures who maintain centuries to millennia-old relationships to the planet’s polar, mountain, and coastal environments, as well as on cities, states and nations whose territorial boundaries are being transformed by ongoing sea level rise (Gerrard and Wannier, 2013 <sup>[[#fn:r26|26]]</sup> ). The scale and cross-boundary dimensions of changes in the ocean and cryosphere challenge the ability of current local, regional and international governance structures to respond (Section 1.7). Profound economic and institutional transformations are needed if climate-resilient development is to be achieved, including ambitious mitigation efforts to avoid the risks of large-scale and abrupt ocean and cryosphere changes.

The commissioning of this IPCC Special Report recognises the interconnected ways in which the ocean and cryosphere are expected to change in a warming climate. SROCC assesses new knowledge since AR5 and provides an integrated approach across IPCC working groups I and II, linking physical changes with their ecological and human impacts, and the strategies to respond and adapt to future risks. It is one of three special reports being produced by the IPCC during its Sixth Assessment Cycle (in addition to the three working groups’ main assessment reports). The concurrent IPCC Special Report on Climate Change and Land (released August 2019) links to SROCC where terrestrial environments and their habitability interact closely with the ocean or cryosphere, such as in mountain, Arctic, and coastal regions. SR15 concluded that human-induced warming will reach 1.5°C between 2030 – 2052 if it continues to increase at the current rate ( ''high confidence'' ), and that there are widespread benefits to human and natural systems of limiting warming to 1.5 o C compared with 2 o C or more ( ''high confidence'' ; IPCC, 2018 <sup>[[#fn:r27|27]]</sup> ).

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