SROCC summary for policymakers In its Summary for Policymakers (SPM), the report said that, since 1970, the "global ocean has warmed unabated" and "has taken up more than 90% of the
excess heat in the climate system." The rate of
ocean warming has "more than doubled" since 1993. Marine heatwaves are increasing in intensity and since 1982, they have "very likely doubled in frequency". Surface acidification has increased as the oceans absorb more CO2.
Ocean deoxygenation "has occurred from the surface to ."
Rising sea levels Global mean sea levels (GMSL) rose by per year which is "2.5 times faster than the rate from 1900 to 1990". At the rate of acceleration, it "could reach around to by 2100 even if greenhouse gas emissions are sharply reduced and global warming is limited to well below 2 °C, but around to if emissions continue to increase strongly. In their summary of the SROCC,
Carbon Brief said that rate of
rising sea levels is "unprecedented" over the past century. Worst-case projections are higher than thought and a rise by 2100 "cannot be ruled out", if greenhouse gas emissions continue to increase strongly."
Ocean deoxygenation The viability of species is being disrupted throughout the
ocean food web due to changes in
ocean chemistry. As the ocean warms,
mixing between water layers decreases, resulting in less oxygen and nutrients being available for
marine life.
Meridional overturning circulation in the Atlantic Chapter 6 which deals with ...,
Atlantic meridional overturning circulation (AMOC) "will very likely weaken over the 21st century" but it is unlikely that AMOC will collapse. A weakening of AMOC would result in "a decrease in marine productivity in the North Atlantic, more winter storms in Europe, a reduction in Sahelian and South Asian summer rainfall, a decrease in the number of tropical cyclones in the Atlantic, and an increase in regional sea-level around the Atlantic especially along the northeast coast of North America."
Carbon Brief described AMOC as "the system of currents in the Atlantic Ocean that brings warm water up to Europe from the tropics. It is driven by the formation of North Atlantic Deep Water – the sinking of cold, salty water in the high latitudes of the North Atlantic."
Melting glaciers There has been an acceleration of glaciers melting in Greenland and Antarctica as well as in mountain glaciers around the world, from 2006 to 2015. This now represents a loss of 720 billion tons (653 billion metric tons) of ice a year.
Ice sheets Carbon Brief said that the melting of Greenland's ice sheets is "unprecedented in at least 350 years." The combined melting of Antarctic and
Greenland ice sheets has contributed "700% more to sea levels" than in the 1990s.
Arctic sea ice decline The
Arctic Ocean could be ice free in September "one year in three" if global warming continues to rise to 2 °C. Prior to industrialization, it was only "once in every hundred years".
Global marine animal biomass and fish catch decline In "Chapter 5: Changing Ocean, Marine Ecosystems, and Dependent Communities", the authors warn that marine organisms are being affected by ocean warming with direct impacts on human communities, fisheries, and food production. The
Times said that it is likely that there will be a 15% decrease in the number of marine animals and a decrease of 21% to 24% in the "catches by fisheries in general" by the end of the 21st century because of climate change.
Decline of snow and lake ice cover In "Chapter 3: Polar Regions", the authors reported that there has been a decline of snow and lake ice cover. From 1967 to 2018, the extent of snow in June decreased at a rate of "13.4 ± 5.4% per decade".
Thawing permafrost Future climate-induced changes to
permafrost "will drive habitat and biome shifts, with associated changes in the ranges and abundance of ecologically-important species." As
permafrost soil melts, there is a possibility that carbon will be unleashed. The permafrost
soil carbon pool is much "larger than carbon stored in plant biomass". "Expert assessment and laboratory soil incubation studies suggest that substantial quantities of C (tens to hundreds Pg C) could potentially be transferred from the permafrost carbon pool into the atmosphere under the
Representative Concentration Pathway (RCP) 8.5" projection.
Low-lying islands and coasts In the final section on low-lying islands and coasts (LLIC), the report says that cities and megacities—including New York City, Tokyo, Jakarta, Mumbai, Shanghai, Lagos And Cairo—are "at serious risk from climate-related ocean and
cryosphere changes." If emissions remain high, some low-lying islands are likely to become "uninhabitable" by the end of the 21st century. Low lying areas including islands and the
Low Elevation Coastal Zone were estimated have approximately 625 million people living in them based on 2000 estimates, with most in "non-developed contexts." ==Reactions==