How warming is driving 'fundamental' changes to ocean

Climate change has disrupted ocean mixing, a process that helps store away most of the world's excess heat and a significant proportion of CO2. Water on the surface is warmer - and therefore less dense - than the water below, a contrast that is intensified by climate change.

Global warming is also causing massive amounts of fresh water to flush into the seas from melting ice sheets and glaciers, lowering the salinity of the upper layer and further reducing its density. This increasing contrast between the density of the ocean layers makes mixing harder, so oxygen, heat and carbon are all less able to penetrate to the deep seas.

Researchers also found that, contrary to their expectations, winds strengthened by climate change had also acted to deepen the ocean surface layer by five to 10 metres per decade over the last half century. A significant number of marine animals live in this surface layer, with a food web that is reliant on phytoplankton. But as the winds increase, the phytoplankton are churned deeper, away from the light that helps them grow, potentially disrupting the broader food web.

The oceans play a crucial role in mitigating the effects of climate change by absorbing around a quarter of man-made CO2 and soaking up more than 90 percent of the heat generated by greenhouse gases, according to the Intergovernmental Panel for Climate Change (IPCC). Scientists are increasingly sounding the alarm over the potential implications of warming on our oceans.

In 2019, research published in the US Proceedings of the National Academy of Sciences calculated that climate change would empty the ocean of nearly a fifth of all living creatures, measured by mass, by the end of the century.