Progress on the Evolutionary Characteristics and Climatic Causes for Warming and Marine Heatwaves in the Coastal China Seas

Over the past decades, the coastal China seas (CCSs) have experienced strong warming and frequent extremely high sea temperature events (marine heatwaves, MHWs), resulting in a series of ecological disasters, including mass mortality of marine organisms and outbreaks of harmful algal bloom. This paper presents a comprehensive review of the research progress involving the warming and MHWs in CCSs, including the characteristics and causes for long-term warming trends and MHWs, as well as their ecological impacts and adaptation strategies. The sea surface temperature (SST) in CCSs, especially in the East China seas (Bohai, Yellow, and East China Seas, hereafter ECSs), has demonstrated an enhanced response to global warming under the combined influences of the East Asian monsoon and Kuroshio, with an annual mean increase of 1.02°C±0.19°C and 1.45°C±0.32°C during 1960–2022, respectively. The interannual and interdecadal variability of SST in CCSs is also teleconnected to large-scale climate modes, such as El Nino–Southern Oscillation (ENSO) and Pacific Decadal Oscillation. Ocean warming has led to rapid northward migration of geographic isotherms and seasonal phenological changes (i.e., spring arrives earlier and fall ends later than normal), resulting in changes in the growth rhythm, geographic distribution, community structure, and ecological service functions of marine organisms. Since 1982, the frequency, intensity, and duration of MHWs in CCSs have increased obviously and are expected to increase further in the future. The frequency of MHWs in ECSs and the South China Sea is 20 and 4 times higher than that in the 1980s, respectively, and these frequencies are highly correlated with the negative Indian Ocean Dipole and the El Niño. Frequent extreme MHWs have resulted in devastating disasters in marine ecosystems, such as mass coral bleaching and mortality. In the future, CCSs, especially the mid-high latitudes of CCSs, will be simultaneously exposed to increased warming, deoxygenation, acidification, and reduced productivity. Marine ecosystems, especially warm-water coral reefs in the South China Sea, are at risk of mass breaching climate tipping points. Therefore, in-depth research on the physical processes and predictability of MHWs, as well as the development of forecasting and early warning systems, are urgently needed. Additionally, transformative climate action measures should be developed to enhance the climate resilience of marine ecosystems, and strong mitigation measures need to be established immediately to slow down global warming.