Ocean temperatures last year were the hottest in recorded history, driving destructive weather around the world and pushing a rise in sea levels.
This is according to research — titled Record-setting Ocean Warmth Continued in 2019 — published this week by a team of scientists from China and the United States in the peer-reviewed Advances in Atmospheric Sciences journal.
Temperatures changes are normally talked about in relation to those on the surface. But 90% of the excess heat created by humans burning fossil fuels, and from other natural sources, is stored in the oceans. Because they are vast, it takes a long time for that heat to start changing the temperature of water.
In the past two decades the oceans heated at four-and-a-half times the rate that they had heated in the three decades before that. The last decade is also the hottest on record.
The data came from the Institute for Atmospheric Physics, the National Oceanic and Atmospheric Administration and the National Centre for Environmental Information. Most of it was collected by about 4 000 floats that drift on the world’s oceans.
That data has become increasingly accurate in recent years.
Some 43% of the heat has gone into the Southern Ocean, which is where South African scientists do a great deal of research.
The biggest visible effect of hotter oceans is in rising sea levels: as ice melts the amount of water increases; the water expands with the heat and takes up more space.
Under the waves, more heat means less dissolved oxygen, which is bad for fish.
On land, more heat means more evaporation. The scientists said this “nourishes heavy rain and promotes flooding”. This in turn leads to “a more extreme hydrological cycle and more extreme weather”.