https://phys.org/news/2019-08-ocean-temperature-common.html
[images in online article]
August 5, 2019
New study: Ocean temperature 'surprises' becoming more common
by Gulf of Maine Research Institute
August 5, 2019—A new study published this week shows how marine
ecosystems around the world are experiencing unusually high ocean
temperatures more frequently than researchers previously expected. These
warming events, including marine heatwaves, are disrupting marine
ecosystems and the people who depend on them.
Dr. Andrew Pershing, Chief Scientific Officer at the Gulf of Maine
Research Institute, led the study, which is entitled "Challenges to
natural and human communities from surprising ocean temperatures," and
published in the Proceedings of the National Academy of Sciences (PNAS).
As part of this new research effort, Dr. Pershing, whose research
previously identified the Gulf of Maine as one of the most rapidly
warming ecosystems in the global ocean, looked at similar warming trends
around the globe.
Dr. Pershing and his colleagues examined 65 large marine ecosystems from
1854-2018 to identify the frequency of surprising ocean temperatures,
which they defined as an annual mean temperature that is two standard
deviations above the mean of the previous three decades.
The researchers identified these "surprises" all over the world,
including the Arctic, North Atlantic, eastern Pacific, and off of
Australia. Moreover, these warming events occurred at nearly double the
rate the scientists expected.
"Across the 65 ecosystems we examined, we expected about six or seven of
them would experience these 'surprises' each year," explains Pershing.
"Instead, we've seen an average of 12 ecosystems experiencing these
warming events each year over the past seven years, including a high of
23 'surprises' in 2016."
The study explores the associated impacts of these warming events on
both natural and human communities.
In natural communities (e.g. coral reefs, fish, plankton, etc.), new
species that prefer warmer conditions can often replace cold-loving
species that suffer when an ecosystem warms. In gradually warming
ecosystems, the changeover of species should be able to keep pace,
according to the study. However, in ecosystems that are experiencing
change much faster, these natural communities are expected to suffer
reductions in both biomass and diversity.
An increase in ocean "surprises" also affects humans. The researchers
explored the challenge rapid ecosystem changes pose to people making
decisions about ocean resources. As the planet continues to warm,
ecosystems and human communities will adapt to the changing conditions.
However, according to the scientists, it is unclear whether such
adjustments will keep pace as the climate trends accelerate.
As part of the study, the research team compared two distinct community
decision-making strategies. Using an economic model, they compared
forward-looking decisions based on climate trends to the results of
decisions made only on historical experiences. They found forward
looking decisions fare much better as the rate of warming increases.
According to the study, many marine ecosystems are already warming fast
enough to apply this decision-making framework.
"We are entering a world where history is an unreliable guide for
decision making," says Pershing. "In a rapidly changing world, betting
that trends will continue is a much better strategy."
As the incidence of these extreme warming events continues to rise, the
results of this study highlight the importance of using climate
projections and other predictive tools to make decisions about the future.
More information: Andrew J. Pershing el al., "Challenges to natural and
human communities from surprising ocean temperatures," PNAS (2019).
www.pnas.org/cgi/doi/10.1073/pnas.1901084116
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