Ocean systems are already facing significant impacts of climate change. At the ocean surface, temperature has on average increased by 0.88  °C from 1850-1900 to 2011-2020 . Marine heatwaves have increased in frequency over the 20th century, with an approximate doubling since the 1980s , and their intensity and duration have also increased  . In the Northeast Pacific, for example, an intense and long-lasting marine heatwave during 2013-2015 bridged to the strong 2015-2016 El Niño  resulted in over 5 years of warmer-than-normal temperatures affecting the migration, distribution and abundance of several marine species, including fisheries resources . The surface open ocean pH has declined globally over the last 40 years by 0.003-0.026 pH per decade , and a decline in the ocean interior pH has been observed in all ocean basins over the past two to three decades  . The ocean is losing dissolved oxygen  in the range of 0.5-3.3% between 1970 and 2010 for the 0-1000 m depth stratum , salt content is being redistributed   and vertical stratification is increasing  . There is high confidence that all these new physical, chemical and biological conditions affect marine organisms' physiology, distribution and ecology, with an overall shift in biomass and species composition affecting ecosystem structure and function . Under climate change, freshwater ecosystems are highly exposed to eutrophication, species invasion and rising temperatures . Major threats to wetland fisheries include water stress, sedimentation, weed proliferation, sea level rise and loss of wetland connectivity .
IPCC
Climate Change 2022: Impacts, Adaptation and Vulnerability
IPCC Report