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

==== 10.4.3.3 Projected Impacts ====

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Water pollution and climate stressors have been considered major challenges to ecosystem sustainability, and now it has been shown that the combined effect these two stressors would be more damaging ( [[#Buchanan--2019|Buchanan et al., 2019]] ). For seagrass beds the pollution stress was found to increase by 2.6% (from 39.7 to 42.3%) when climate factors were added. Assuming the pollution levels remain at the 2014 levels, different scenarios including RCP2.6 and RCP8.5 were worked out for the Bohai Sea, and the results indicated amplification of the impacts on the ecosystem. Pollutants like petroleum hydrocarbons, dissolved inorganic nitrogen and soluble reactive phosphorus were the major pollution stressors ( [[#Lu--2018|Lu et al., 2018]] ). In the future, policies that focus strictly on pollution control should be changed and take into account the interactive effects of climate change for better forecast and management of potential ecological risks ( [[#Lu--2018|Lu et al., 2018]] ).

Projected changes in catch potential (in percent) by 2050 and 2100 relative to 2000 under RCP2.6 and RCP8.5, based on outputs from the dynamic bioclimate envelop model and the dynamic size-based food-web models, indicate that the marine and coastal resources of most Asian countries will be impacted with varying intensity ( [[#FAO--2018b|FAO, 2018b]] ).

Better management of resources through projections of resource distribution, abundance and catch is required; however, lack of data (e.g., oceanographic surveys) and scientific knowledge is a constraint to this aim ( [[#Maung%20Saw%20Htoo--2017|Maung Saw Htoo et al., 2017]] ). Effective forecasts of areas of resource abundance based on habitat preference have to be worked out for Asian regions.

Modelling and assessment of the vulnerability and habitat suitability of the Persian Gulf for 55 species to climate change indicated that there is a high rate of risk of local extinction in the southwest part of the Persian Gulf, off the coast of Saudi Arabia, Qatar and the United Arab Emirates (UAE). Likelihood of reduced catch was observed, and Bahrain and Iran were found to be more vulnerable to climate change ( [[#Wabnitz--2018|Wabnitz et al., 2018]] ). Projected changes in fish catches can impact the supply of fish available for local consumption (i.e., food security) and exports (i.e., income generation) ( [[#Wabnitz--2018|Wabnitz et al., 2018]] ). As per ( [[#UNESCAP--2018a|UNESCAP, 2018a]] ), over 40% of coral reefs and 60% of coastal mangroves in the Asia-Pacific region have already been lost, and approximately 80% of the region’s coral reefs are currently at risk.

Regionally, the escalation in thermal stress estimated for the different global warming scenarios is greatest for Southeast Asia and least for the Pacific Ocean ( [[#Lough--2018|Lough et al., 2018]] ). For the 100 reef locations examined here and given current rates of warming, the 1.5°C global warming target represents twice the thermal stress they experienced in 2016 ( [[#Lough--2018|Lough et al., 2018]] ).

In the Southeast Asia region threats from both warming and acidification has indicated that by 2030, 99% of reefs will be affected, and by 2050, 95% are expected to be in the highest levels of the ‘threatened’ category ( [[#Burke--2011|Burke et al., 2011]] ), similar to global corals ( [[#Frieler--2013|Frieler et al., 2013]] ; [[#Bruno--2016|Bruno and Valdivia, 2016]] ). Modelling results indicate that even under RCP scenarios, the functional traits of coral reefs can be affected ( [[#van%20der%20Zande--2020|van der Zande et al., 2020]] ) and coral communities will mainly consist of small numbers of temperature-tolerant and fast-growing species ( [[#Kubicek--2019|Kubicek et al., 2019]] ). Increases in temperature (+3°C) and ''p'' CO2 (+400 matm) projected for this century can reduce the sperm availability for fertilisation, which along with adult population decline either due to climate change or anthropogenic impacts ( [[#Hughes--2017|Hughes et al., 2017]] ) can affect coral reproductive success thereby reducing the recovery of populations and their adaptation potential ( [[#Albright--2013|Albright and Mason, 2013]] ; [[#Hughes--2018|Hughes et al., 2018]] ; [[#Jamodiong--2018|Jamodiong et al., 2018]] ). In the southern Persian Gulf, increased disturbance frequency and severity has caused progressive reduction in coral size, cover and population fecundity ( [[#Riegl--2018|Riegl et al., 2018]] ), and this can lead to functional extinction. Connectivity required to avoid extinctions has increased exponentially with disturbance frequency and correlation of disturbances across the metapopulation. In the Philippines experiments have also proved that scleractinian corals, such as ''A. tenuis, A. millepora'' and ''F. colemani'' , which spawn their gametes directly into the water column, may experience limitations from sperm dilution and delays in initial sperm–egg encounters that can impact successful fertilisation ( [[#de%20la%20Cruz--2020|de la Cruz and Harrison, 2020]] ).

Apart from these threats, natural hazards have also been found to affect coral reefs of Asia. The extensive and diverse coral reefs of Muscat, Oman, in the northeast Arabian Peninsula were found to have long-term effects from Cyclone Gonu, which struck the Oman coast in June 2007, more than coastal development ( [[#Coles--2015|Coles et al., 2015]] ).

Sandy beaches are subject to highly dynamic hydrological and geomorphological processes, giving them more natural adaptive capacity to climate hazards ( [[#Bindoff--2019|Bindoff et al., 2019]] ). Progress is being made towards models that can reliably project beach erosion under future scenarios despite the presence of multiple confounding drivers in the coastal zone (Chapter 3). Assuming minimal human intervention and projected impacts of SLR by 2100 under RCP8.5-like scenarios, 57–72% of Thai beaches (Ritphring, 2018), at least 50% loss of area on around a third of Japanese beaches (Mori, 2018) will disappear.

Marine heatwaves (MHWs) in Asia have been making changes to the structure and functioning of coastal and marine ecosystems ( [[#Kim--2017|Kim and Han, 2017]] ; [[#Oliver--2017|Oliver et al., 2017]] ; [[#Frölicher--2018|Frölicher and Laufkötter, 2018]] ; [[#Oliver--2019|Oliver et al., 2019]] ; [[#Smale--2019|Smale et al., 2019]] ), affecting resources like copepods ( [[#Doan--2019|Doan et al., 2019]] ) and coral reefs ( [[#Zhang--2017c|Zhang et al., 2017c]] ). Coral reefs of the southeast Indian Ocean have been affected by MHWs ( [[#Zhang--2017c|Zhang et al., 2017c]] ).

Simulation of RCP scenarios have shown that continued warming can drive a poleward shift in distribution of the seaweed ''Ecklonia cava'' of Japan, and under the lowest-emissions scenario (RCP2.6) most populations may not be impacted, but under the highest-emissions scenario (RCP8.5) the existing habitat may become unsuitable and it can also increase predation by herbivorous fishes ( [[#Takao--2015|Takao et al., 2015]] ).

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