Study: Heat buildup in oceans
By Chris Mooney and Brady Dennis
The Washington PostThe world’s oceans have been soaking up far more excess heat
in recent decades than scientists realized, suggesting that Earth could be set to
warm even faster than predicted in the years ahead, according to new research
Over the past quarter century, Earth’s oceans have retained 60 percent more
heat each year than scientists previously had thought, said Laure Resplandy,
a geoscientist at Princeton University who led the startling study published Wednesday
in the journal Nature. The difference represents an enormous amount of additional
energy, originating from the sun and trapped by the Earth’s atmosphere — more than
eight times the world’s energy consumption, year after year.
In the scientific realm, the new findings help to resolve long-running doubts
about the rate of the warming of the oceans prior to the year 2007, when reliable
measurements from devices called “Argo floats” were put to use worldwide.
Before that, different types of temperature records — and an overall lack of them
— contributed to murkiness about how quickly the oceans were heating up.
The higher-than-expected amount of energy in the oceans means more heat is
being retained within the Earth’s climate system each year, rather than escaping
into space. In essence, more heat in the oceans signals that global warming itself
is more advanced than scientists thought.
“We thought that we got away with not a lot of warming in both the ocean and
the atmosphere for the amount of CO2 that we emitted,” said Resplandy, who
published the work with experts from the Scripps Institution of Oceanography
and several other institutions in the U.S., China, France, and Germany. “But
we were wrong. The planet warmed more than we thought. It was hidden from
us just because we didn’t sample it right. But it was there. It was in the ocean already.”
Wednesday’s study also could have important policy implications. If ocean
temperatures are rising more rapidly than previously calculated, that could leave
nations even less time to dramatically cut the world’s emissions of carbon dioxide,
in hopes of limiting global warming to the ambitious goal of 2.7 degrees Fahrenheit
above pre-industrial levels.
The world already has warmed 1.8 degrees Fahrenheit since the late 19th century.
Scientists backed by the United Nations reported this month that with warming
projected to increase steadily, the world faces a daunting challenge in trying to limit
that warming to only another half degree Celsius. The group found that it would take
“unprecedented” action by leaders across the globe over the coming decade to
even have a shot at that goal.
Meanwhile, the Trump administration has continued to roll back regulations aimed
at reducing carbon emissions from vehicles, coal plants and other sources and
has said it intends to withdraw from the Paris climate accord. In one instance,
he administration relied on an assumption that the planet will warm a disastrous 7
degrees Fahrenheit, or about 4 degrees Celsius, by the end of the century in arguing
that a proposal to ease vehicle fuel-efficiency standards would have only minor climate impacts.
The new research underscores the potential consequences of global inaction. Faster warming
oceans mean that seas will rise faster and that more heat will be delivered to critical locations
that already are facing the effects of a warming climate, such as coral reefs in the tropics and
the ice sheets of Greenland and Antarctica.
“In case the larger estimate of ocean heat uptake turns out to be true, adaptation to — and mitigation of — our changing climate would become more urgent,” said Pieter Tans, leader of the Carbon Cycle Greenhouse Gases Group at NOAA, who was not involved in the study.
The oceans absorb more than 90 percent of the excess energy trapped within the
The new research does not measure the ocean’s temperature directly. Rather,
it measures the volume of gases, specifically oxygen and carbon dioxide, that
have escaped the ocean in recent decades and headed into the atmosphere as it
heats up. The method offered scientists a reliable indicator of ocean temperature
change because it reflects a fundamental behavior of a liquid when heated.
“When the ocean warms, it loses some gas to the atmosphere,” said Resplandy.
“That’s an analogy that I make all the time: if you leave your Coke in the sun, it
will lose the gas.”
This approach allowed researchers to recheck the contested history of ocean
temperatures in a different and novel way. In doing so, they came up with a higher
number for how much warming the oceans have experienced over time.
“I feel like this is a triumph of earth system science. That we could get confirmation
from atmospheric gases of ocean heat content is extraordinary,” said Joellen Russell,
a professor and oceanographer at the University of Arizona. “You’ve got the A-team here on this paper.”
But Russell said the findings themselves are hardly as uplifting.
“(It) does have implications for climate sensitivity, meaning how warm does a
certain amount of CO2 make us,” Russell said, adding that the world could have a
smaller “carbon budget” than once thought.