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A satellite image of the blue planet, September 10, 2020. Image: keystone
The seas are sweating, and more and more often
Heat waves are hitting the world’s oceans with increasing frequency because humans fuel climate change. This is what researchers from the University of Bern report.
Dead seabirds, collapsed fish populations and discolored coral – these are just a few examples of the negative effects heat waves can have on the oceans. Many marine ecosystems need long recovery times, “if they ever fully recover,” first author Charlotte Laufkötter said in a statement from the University of Bern on Thursday.
The marine scientist and her team evaluated satellite measurements of the water temperature of all oceans between 1981 and 2017. As a result, heat waves have gotten longer and hotter in the last 40 years.
Hotter and longer heat waves
The 27 major heat waves that occurred in the first decade examined lasted an average of 32 days. They reached maximum temperatures of 4.8 degrees Celsius above the long-term average temperature. In the last decade analyzed, however, there were 172 extreme events. They lasted an average of 48 days and peaked 5.5 degrees above the long-term average.
There is a general trend towards the causes of the most frequent heat waves. In the course of global warming, surface water has risen by an average of 0.6 degrees, regionally up to 1 degree, Laufkötter said. In addition, there are individual reasons for each heat wave: hot air masses above, changes in ocean currents or large-scale climatic oscillations, which are related to the El Niño weather phenomenon.
Marine heat waves will soon be the norm
To determine the influence of humans on the seven most devastating heat waves, the researchers carried out so-called attribution studies. These can be used to estimate the extent to which extreme events carry the human signature. To this end, the Bern team created two worlds using simulations: a real one with increasing concentrations of greenhouse gases in the atmosphere and a fictitious one without an increase in greenhouse gases.
According to them, large heat waves in the world’s oceans have become more than 20 times more frequent due to humans and, according to the researchers, they should become the norm as the temperature rises. “To reduce the risk of unprecedented marine heat waves, ambitious climate targets are absolutely necessary,” Laufkötter said. This is the only way to avoid the irrevocable loss of valuable ecosystems. (sda)
