Oceans On Simmer

The world's oceans will witness marine heatwaves, sea ice-free Arctic, severe cyclones

- M Rajeevan

Oceans regulate the climate by absorbing atmospheric carbon dioxide (CO2) and by altering the energy budget, carbon cycle and nutrient cycle. They have helped reduce the worst impacts of climate change by absorbing over 90 per cent of excess global temperature rise and about 25 per cent of CO2 emission. However, global warming is causing (i) warming, (ii) acidification and (iii) deoxygenation of oceans.

The oceans have warmed unabated since 2005, continuing the clear multidecadal trends documented by the Intergovernmental Panel on Climate Change (IPCC). At the ocean surface, temperature has on average increased by 0.88°C from 1850-1900 to 2011-20, with 0.60°C of this warming having occurred since 1980. The ocean surface temperature is projected to increase by about 1.5°C by the 2050s with respect to the 1850-1990 threshold. The rise has been observed not only at the surface but also in deep ocean waters. The major impact of ocean warming is seen over the Arctic Ocean which will likely become practically sea ice-free during the seasonal sea ice minimum for the first time before 2050.

It is virtually certain that global mean sea level will rise through the 2050s because all contributors to global the mean sea level will likely continue. Relative to 1995-2014, the global mean sea level will rise 0.18-0.23 m by 2050 and by 0.38-0.77 m by 2100. The rise is mainly due to thermal expansion and mass loss from glaciers and ice sheets.