Editing IPCC:AR6/SR15/Chapter-3 (section)

==== 3.4.4.7 Loss of sea ice ====

<div id="section-3-4-4-7-block-1"></div>

Sea ice is a persistent feature of the planet’s polar regions (Polyak et al., 2010) <sup>[[#fn:r621|621]]</sup> and is central to marine ecosystems, people (e.g., food, culture and livelihoods) and industries (e.g., fishing, tourism, oil and gas, and shipping). Summer sea ice in the Arctic, however, has been retreating rapidly in recent decades (Section 3.3.8), with an assessment of the literature revealing that a fundamental transformation is occurring in polar organisms and ecosystems, driven by climate change ( ''high confidence'' ) (Larsen et al., 2014) <sup>[[#fn:r622|622]]</sup> . These changes are strongly affecting people in the Arctic who have close relationships with sea ice and associated ecosystems, and these people are facing major adaptation challenges as a result of sea level rise, coastal erosion, the accelerated thawing of permafrost, changing ecosystems and resources, and many other issues (Ford, 2012; Ford et al., 2015) <sup>[[#fn:r623|623]]</sup> .

There is considerable and compelling evidence that a further increase of 0.5°C beyond the present-day average global surface temperature will lead to multiple levels of impact on a variety of organisms, from phytoplankton to marine mammals, with some of the most dramatic changes occurring in the Arctic Ocean and western Antarctic Peninsula (Turner et al., 2014, 2017b; Steinberg et al., 2015; Piñones and Fedorov, 2016) <sup>[[#fn:r624|624]]</sup> .

The impacts of climate change on sea ice are part of the focus of the IPCC Special Report on the Ocean and Cryosphere in a Changing Climate (SROCC), due to be released in 2019, and hence are not covered comprehensively here. However, there is a range of responses to the loss of sea ice that are occurring and which increase at 1.5°C and further so with 2°C of global warming. Some of these changes are described briefly here. Photosynthetic communities, such macroalgae, phytoplankton and microalgae dwelling on the underside of floating sea ice are changing, owing to increased temperatures, light and nutrient levels. As sea ice retreats, mixing of the water column increases, and phototrophs have increased access to seasonally high levels of solar radiation ( ''medium confidence'' ) (Dalpadado et al., 2014; W.N. Meier et al., 2014) <sup>[[#fn:r625|625]]</sup> . These changes are expected to stimulate fisheries productivity in high-latitude regions by mid-century ( ''high confidence'' ) (Cheung et al., 2009, 2010, 2016b; Lam et al., 2014) <sup>[[#fn:r626|626]]</sup> , with evidence that this is already happening for several high-latitude fisheries in the Northern Hemisphere, such as the Bering Sea, although these ‘positive’ impacts may be relatively short-lived (Hollowed and Sundby, 2014; Sundby et al., 2016) <sup>[[#fn:r627|627]]</sup> . In addition to the impact of climate change on fisheries via impacts on net primary productivity (NPP), there are also direct effects of temperature on fish, which may in turn have a range of impacts (Pörtner et al., 2014) <sup>[[#fn:r628|628]]</sup> . Sea ice in Antarctica is undergoing changes that exceed those seen in the Arctic (Maksym et al., 2011; Reid et al., 2015) <sup>[[#fn:r629|629]]</sup> , with increases in sea ice coverage in the western Ross Sea being accompanied by strong decreases in the Bellingshausen and Amundsen Seas (Hobbs et al., 2016) <sup>[[#fn:r630|630]]</sup> . While Antarctica is not permanently populated, the ramifications of changes to the productivity of vast regions, such as the Southern Ocean, have substantial implications for ocean foodwebs and fisheries globally.

<div id="section-3-4-4-8"></div>

<span id="sea-level-rise"></span>