Effects of “unprecedented” marine heat waves may be irreversible
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July marked Earth’s hottest temperatures ever, and heat
waves are currently affecting over 44% of ocean area, making the current marine
heat wave the most widespread ever recorded. Scientists at the National Oceanic
and Atmospheric Administration (NOAA) expect that number to rise to over 50% by this
fall. Usually, about 10% of the world’s oceans experience a heatwave at any
given time.
The levels of marine heat waves this year are
“unprecedented,” said Dillon Amaya, a scientist who studies climate extremes at
the NOAA.
The marine heat wave could lead to a redistribution of
ocean species that may then also destabilize additional ecosystems, according
to Jenn Caselle, a research biologist at the University of California, Santa
Barbara’s Marine Science Institute.
“These marine communities that are reshuffling right now could stay in those reshuffled states and become our new normal,” said Caselle.
Cascade of problems
Concern for coral is
one example of the cascade of problems that can occur. Bleached corals can
spell death for fish and invertebrates that rely on coral ecosystems for food
and shelter. Once corals are bleached, they rarely recover.
From 2013-2017, a heat wave wreaked havoc in the Pacific,
driving large numbers of sea urchins north to cooler waters where they fed on
kelp, ultimately decimating kelp populations in the waters off of Northern
California. The current Pacific heat wave has a similar potential to cause a
reshuffling of marine life, with wildlife that prefers warmer water replacing
that which prefers colder water, said Caselle.
The redistribution of species also effects humans. The
kelp decimation during the 2013-2017 Pacific heat wave triggered a decline in
abalone populations, cutting off the California abalone fishing industry.
In the Northeast, the redistribution effect has meant that some species are moving outside of areas where fishermen are permitted to catch them, said Vincent Saba, a fisheries scientist with NOAA’s Northeast Fisheries Science Center.
For example, populations of summer flounder, one of
the most sought-after commercial fish in the Atlantic, have shifted northward and
into deeper, cooler waters, threatening the
livelihoods of fishing communities.
Similar issues among commercial species are likely to
arise as more widespread marine heat waves happen, said Caselle. “It’s going to
take human communities some time to adapt.”
Shifting baselines
While this year’s heat waves are extreme weather events
compared to a few decades ago, they’re not actually abnormal compared to
current climate conditions. Ocean temperatures have warmed about 0.12 degrees
Fahrenheit per decade since pre-industrial times, meaning that ocean
temperatures that seemed extreme decades ago are becoming common today,
according to a paper published
in the journal Nature in April.
“This is the new normal,” said Saba, one of the authors
of the Nature paper.
Conservation actions, such as protecting wide areas of
the ocean from fishing, can only do so much to prevent ecosystem disturbance
from such heat waves, according to a study published
by Caselle this month. The most important way to protect the oceans from heat
effects is to halt climate change as quickly as possible, she said.
Most Americans, however, don’t consider climate change or
the environment as a top concern, according to recent polling. And
scientists agree that the
current actions world governments have taken to halt climate change are not
sufficient to keep warming under the limits set by the 2016 Paris Agreement.
“We can build all the marine protected areas in the
world, and we can try to convince the fisheries managers to be proactive in the
face of loss,” said Caselle. “But if we don’t stop burning fossil fuels and
emitting, there’ll be a point where there’s only so much we can do,” she said.