Pacific Winds Responsible for Global Warming Slowdown: Study

By: By Terrell Johnson

Published: February 10,2014

 

 

 

There is perhaps no more hotly debated topic in climate science today than the global warming pause or "hiatus," the oft-cited slowdown in surface warming that's been taking place since about 1998.
To some, this has put the central argument behind human-caused climate change – that the buildup in the atmosphere of fossil fuel emissions from power plants, factories, cars and other industrial activity is warming the planet to a dangerously high level – in jeopardy.
But according to a paper published Feb. 9 in the scientific journal Nature Climate Change, there's good reason to believe the hiatus is a temporary phenomenon caused by an unprecedented strengthening of trade winds over the Pacific Ocean and that rapid warming"will resume when, not if, it goes away.
These winds have changed ocean circulation patterns and driven tremendous amounts of heat into the western Pacific while cooling the eastern Pacific, the study's lead author Matthew England told the Sydney Morning Herald.
The paper goes into great detail – you can read the full version here – but these are some of its most striking findings:

1) Pauses are a normal part of long-term global warming

The most recent pause in global warming follows a much longer one that lasted from about the mid 1940s to the late 1970s. You can see it in this chart of temperature anomalies from 1850 to the present day:

WMO

Here's how the Australian-led team of scientists who authored the Nature Climate Change study describe it:
"Decadal periods of minimal warming, or even cooling, interspersing decades of rapid warming, are not inconsistent with a long-term warming trend; indeed this characterizes the interplay between steadily increasing greenhouse gas forcing and internally generated climate variability," they write.
Factors other than natural variability – like volcanic eruptions, which (if large enough) can temporarily cool the planet – also sometimes play a role, they add. "Indeed, hiatus decades are expected to punctuate future warming trends, even under scenarios of rapid global warming."

2) The current pause could keep going for a while

If the much-stronger-than-normal trade winds the scientists found in the Pacific keep going – which are helping to keep the tropical Pacific cool as well as other ocean circulation patterns, contributing to cooler global average surface temperatures in recent years – the current hiatus could persist until nearly 2020.

ThinkStock

This would mean that the current hiatus would closely resemble the long pause in warming that occurred between the 1940s and the 1970s, with little surface air warming beyond the 2001 to 2010 average.
But if there is a slackening in the Pacific winds described in the study, then the current hiatus won't last much longer. "The model suggests the present hiatus will be short-lived, with rapid warming set to resume soon after the wind trends reverse," the study adds.

3) We've seen a plateau in warming, but maybe we should have seen global cooling instead

In an interview with the Sydney Morning Herald, England pointed out the massive amount of heat the Pacific has absorbed over the past 20 years, as some regions of the ocean have risen as much as 3°C (5.4°F) at depths of between 100 and 300 meters (about 330 to 980 feet).
“The question might be why hasn’t the world actually cooled over the past 10 years," England said, "rather than plateaued?”

WILLIAM WEST/AFP/Getty Images

A woman cools off with fans and mist put out for spectators as a heat wave continues to sizzle on day three of the 2014 Australian Open tennis tournament in Melbourne on January 15, 2014.

Thirteen of the 14 hottest years on record have all occurred since the 21st century began, while the United States had its hottest year on record in 2012 and last year brought one of the world's 10 hottest years since modern temperature records began in the late 1800s.
In the past, the stronger-than-normal Pacific trade winds have typically lasted for periods of about 20 to 30 years, England said. When they die down – which they will sooner or later, he added – "it’s highly likely that air temperature change over the planet will be one of relatively rapid warming, probably exceeding the warming rate of the 80s and 90s."
The reason, he added, is because the level of greenhouse gases in the atmosphere today is much higher than it was 30 years ago. “If you pump heat into the ocean, it’s just sitting there waiting to be given back,” he said.
Read the full study at Nature Climate Change.
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