A Cooler Pacific May Be Behind Recent Pause in Global Warming
A study in the journal Nature could help explain why the Earth’s average temperature hasn’t increased during the past 15 years — despite a long-term trend of global warming.
The Earth’s average temperature has risen by more than 1 degree Fahrenheit since the beginning of the Industrial Revolution. But the temperature rise has not been moving in lock step with the rise of carbon dioxide in the atmosphere. Carbon dioxide — mainly from burning fossil fuels — traps heat in the air.
Now scientists at the Scripps Institution of Oceanography have more evidence that this global “pause” has to do with conditions in the Pacific Ocean.
“We started the study trying to resolve several contradictions,” says Shang-Ping Xie.
He and a colleague asked why the global average temperature has bucked its long-term upward trend. And they also set out to explain why — even during this hiatus — there has been record melting of ice in the Arctic Ocean, and why there have been many new summertime heat records.
Xie says he can explain a lot of that simply by looking at what’s been happening in the tropical waters of the Pacific Ocean. Waters there have been relatively cool, and that means the ocean can take up more heat than usual.
“It’s gaining extra heat during the past 15 years, and that heat is being stored” in the deep ocean, he says.
There’s no telling how long this cool phase will persist. But the previous Pacific cool phase, which started in the 1940s, lasted about 30 years. It can’t last forever — the ocean will eventually return to a warm phase, “and when that happens, we will be seeing unprecedented rates of climate warming,” he says.
Not only will we get the natural heat wave, but on top of that we’ll get all the warming from greenhouse gases that have been building up during this cold cycle.
Xie says he can also explain the continuing summer heat records and melting Arctic ice. It turns out that the plateau in global average temperatures is mostly the result of lower temperatures during the wintertime.
That drags down the average, “but if you go to the summer season, actually the global mean temperature has kept rising for the past 15 years,” he says. “That allows heat waves to set records, and it allows the Arctic Ocean to melt at a record pace.”