Marine heatwaves are human-made

Date:
September 25, 2020
Source:
University of Bern
Summary:
Heatwaves in the world's oceans have become over 20 times more
frequent due to human influence. This is what researchers are
now able to demonstrate. Marine heatwaves destroy ecosystems and
damage fisheries.



FULL STORY ==========================================================================
A marine heatwave (ocean heatwave) is an extended period of time in which
the water temperature in a particular ocean region is abnormally high. In recent years, heatwaves of this kind have caused considerable changes to
the ecosystems in the open seas and at the coast. Their list of negative effects is long: Marine heatwaves can lead to increased mortality among
birds, fish and marine mammals, they can trigger harmful algal blooms,
and greatly reduce the supply of nutrients in the ocean. Heatwaves also
lead to coral bleaching, trigger movements of fish communities to colder waters, and may contribute to the sharp decline of the polar icecaps.


========================================================================== Researchers led by Bern-based marine scientist Charlotte Laufko"tter
have been investigating the question of how anthropogenic climate
change has been affecting major marine heatwaves in recent decades. In
a study recently published in the well-known scientific journal Science, Charlotte Laufko"tter, Jakob Zscheischler and Thomas Fro"licher concluded
that the probability of such events has increased massively as a result
of global warming. The analysis has shown that in the past 40 years,
marine heatwaves have become considerably longer and more pronounced in
all of the world's oceans. "The recent heatwaves have had a serious impact
on marine ecosystems, which need a long time to recover afterwards --
if they ever fully recover," explains Charlotte Laufko"tter.

A huge increase since the 1980s In its investigations, the Bern team
studied satellite measurements of the sea surface temperature between
1981 and 2017. It was found that in the first decade of the study period,
27 major heatwaves occurred which lasted 32 days on average. They reached maximum temperatures of 4.8 degrees Celsius above the long-term average temperature. In the most recent decade to be analyzed, however, 172 major events occurred, lasting an average of 48 days and reaching peaks of 5.5 degrees above the long-term average temperature. The temperatures in the
sea usually fluctuate only slightly. Week-long deviations of 5.5 degrees
over an area of 1.5 million square kilometers -- an area 35 times the
size of Switzerland -- present an extraordinary change to the living
conditions of marine organisms.

Statistical analyses demonstrate human influence For the seven marine
heatwaves with the greatest impact, researchers at the University of
Bern carried out what is referred to as attribution studies.

Statistical analyses and climate simulations are used to assess the
extent to which anthropogenic climate change is responsible for the
occurrence of individual extremes in the weather conditions or the
climate. Attribution studies typically demonstrate how the frequency of
the extremes has changed through human influence.

Without ambitious climate goals, marine ecosystems might disappear
According to the findings of the attribution studies, major marine
heatwaves have become more than 20 times more frequent due to human
influence. While they occurred every hundred or thousand years in
the pre-industrial age, depending on the progress of global warming,
in the future they are set to become the norm. If we are able to
limit global warming to 1.5 degrees, heatwaves will occur once every
decade or century. If temperatures rise by 3 degrees, however, extreme situations can be expected to occur in the world's oceans once per
year or decade. "Ambitious climate goals are an absolute necessity
for reducing the risk of unprecedented marine heatwaves," emphasizes
Charlotte Laufko"tter.

"They are the only way to prevent the irreversible loss of some of the
most valuable marine ecosystems."

========================================================================== Story Source: Materials provided by University_of_Bern. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. Charlotte Laufko"tter, Jakob Zscheischler, Thomas
L. Fro"licher. High-
impact marine heatwaves attributable to human-induced global
warming.

Science, September 25, 2020 DOI: 10.1126/science.aba0690 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/09/200925113351.htm

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