Editing IPCC:AR6/WGII/Chapter-10 (section)

==== 10.4.3.2 Observed Impacts ====

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Primary production in the western Indian Ocean showed a reduction by 20% during the past six decades, attributed to rapid warming and ocean stratification which restricted nutrient mixing ( [[#Roxy--2016|Roxy et al., 2016]] ). Variation in secondary-production zooplankton densities and biomass in the East Asian Marginal Seas affected the recruitment of fishes due to mismatch in spawning period and larval-feed availability during the last three climate regime shifts (CRS) in the mid-1970s, late 1980s and late 1990s, which were characterised by the North Pacific index and the Pacific Decadal Oscillation index (Kun [[#Jung--2017|Jung et al., 2017]] ). In the western North Pacific, climate change has affected recruitment and the population dynamics of pelagic fishes, such as sardine and anchovy ( [[#Nakayama--2018|Nakayama et al., 2018]] ), and also shifts in the spawning ground and extension of the spawning period of the chub mackerel ''Scomber japonicas'' ( [[#Kanamori--2019|Kanamori et al., 2019]] ).

Varied responses to CRS in the China seas have been observed for small pelagic fishes ( [[#Ma--2019|Ma et al., 2019]] ) and cephalopods ( [[#Ichii--2017|Ichii et al., 2017]] ). The winter and summer SSTs have shown evidence of decadal variability with abrupt changes from cold to warm in substantial association with climate indices to which coastal cephalopods in the China seas respond differentially, with some benefiting from warmer environments while others respond negatively ( [[#Pang--2018|Pang et al., 2018]] ). In the western and eastern North Pacific marine ecosystem, it is indicated that groundfish may suffer more than pelagic fish ( [[#Yati--2020|Yati et al., 2020]] ). Habitat Suitability index models using SST, chlorophyll- ''a'' , sea surface height anomaly (SSHA) and sea surface salinity (SSS), as well as fishing effort, strongly indicate that Neon flying squid is affected by interannual environmental variations and undertakes short-term migrations to suitable habitat, affecting the fisheries ( [[#Yu--2015|Yu et al., 2015]] ). The 2015–2016 El Niño was found to impact coral reefs of shallower regions (depth of 5–15 m) in South Andaman, India, more than those beyond 20 m ( [[#Majumdar--2018|Majumdar et al., 2018]] ). On the southeast coast of India, with bleaching largely mediated by the SST anomaly and during the recovery period, macroalgae outgrowth has been observed (2.75%) indicating impacts on the benthic community ( [[#Ranith--2019|Ranith and Kripa, 2019]] ). In the South China Sea, the increase in SST was found to be higher than predicted in recent decades, while the pH decreased at a rate of 0.012–0.014 yr –1 , more than the predicted level, due to high microbial respiratory processes releasing CO 2 ( [[#Yuan--2019|Yuan et al., 2019]] ). Simulation experiments have shown differential adaptation capacity of common species (Zheng, 2019; [[#Yuan--2019|Yuan et al., 2019]] ).

The UN’s (2019) report on climate action and support trends highlights that the impacts of climate change on coastal ecosystems are mainly increased risks due to flooding, inundation due to extreme events, coastal erosions, ecosystem processes and, in the case of fisheries, variations in population or stock structures due to ocean circulation pattern, habitat loss degradation and ocean acidification. Analysis of data on the occurrence of varied natural hazards from 1900 to 2019 has shown that tropical cyclones, riverine floods and droughts have increased significantly, and the impacts of these events on coastal communities are also severe and destructive. The UN’s average score for SDG Goal 14 (Life Under Water) for Asia was estimated as 46 among the scores of 40 nations, and the Ocean Health Biodiversity index was comparatively high (average 87.9); however, the indices show that more region-specific action plans are required to achieve the UN 2030 goal for Life Under Water.

Apart from the human impacts, the ecology and resource abundance of coastal waters have been found to be impacted by extreme events. During tropical cyclones ecological variations, like lowering of SST, an increase in chlorophyll- ''a'' and a decrease in oxygen ( [[#Chacko--2019|Chacko, 2019]] ; [[#Girishkumar--2019|Girishkumar et al., 2019]] ) have been observed. Global analyses of such events have indicated that they may have an impact on the fishery directly by creating unfavourable ecological conditions and destruction of critical habitats indirectly by affecting the eggs and larvae as well as subsequent fishery recruitment ( [[#McKinnon--2003|McKinnon et al., 2003]] ; [[#Bailey--2016|Bailey and Secor, 2016]] ). In the South China Sea in July 2000, during a 3-day cyclone period, an estimated thirtyfold increase in surface chlorophyll- ''a'' concentration was observed ( [[#Lin--2003|Lin et al., 2003]] ). The estimated carbon fixation resulting from this event alone is 0.8 Mt, or 2–4% of the SCS’s annual new production ( [[#Lin--2003|Lin et al., 2003]] ). Since an average of 14 cyclones pass over this region annually, the contribution of cyclones to the annual new production has been estimated to be as high as 20–30% ( [[#Lin--2003|Lin et al., 2003]] ).

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