'Halted' Global-Warming Tied to Pacific Cooling

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Did climate scientists get it wrong?

Despite all indications to the contrary — the record breaking heat waves in North America, carbon dioxide levels exceeding 400 parts per million at the Mauna Loa observatory last May, the record melting of Arctic sea ice — the global temperature has remained constant over the past 15 years. Too constant.

A climate model shoes the change in temperature from the late 20th century to the middle of the 21st century due to rising greenhouse gas emissions. The left panel shows the average between June and August, and the right panel between December and February. Courtesy: NOAA.

Scientists had been expecting it to rise. So, did they get some part of carbon dioxide’s effect on the climate wrong?

Not at all, and the respite from warming is just temporary, according a new study published today in Nature. The reason for the pause is the tropical Pacific Ocean, which has cooled down for the past decade. The cooling has so far canceled out the warming

But the cooling will stop someday, and when it does, global temperatures will continue to rise.

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The system that caused the tropical Pacific to cool down is the El Niño/La Niña (ENSO), which are known to affect hurricane seasons in the U.S. The system swings back and forth between a warm and a cold phase — it was in a cold phase  between the 1940s to the 1970s, and it switched to a warm phase up until 1998. Since then, it has been in a cold phase, said Yu Kosaka, a scientist at the Scripps Institute of Oceanography at the University of California and co-author of the report.

The study uses climate models based on intricate computing. The model is called the Geophysical Fluid Dynamics Laboratory (version 2.1), sophisticated software developed by the National Oceanic and Atmospheric Administration that tries to replicate, as simply as possible, the planet’s complex climate.

The model breaks down the world into a three-dimensional grid, with each cube describing natural phenomena within it using mathematical equations. They include numerical representations for the atmosphere, the land, the ocean and sea ice, and equations say how they relate to each other. A supercomputer crunches away at the numbers and ultimately reveals the pace of warming every time carbon dioxide doubles in the atmosphere.

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It’s a experiment used widely by climate modelers, including the Intergovernmental Panel on Climate Change (IPCC) in its massive report to be unveiled on September 27.

The IPCC currently states that the global temperatures will rise by between 2 and 4.5 degrees Celsius when carbon dioxide in the atmosphere doubles. But given that global temperatures have not risen since 1998, some have suggested that temperatures will be at the lower part of the range. That would be good news for humans because it would give us a bit more time to deal with the climate problem.

But Kosaka’s work suggests that scientists have not overestimated the sensitivity of climate to carbon dioxide.

So, humanity is as much on course toward a climate catastrophe as it was 15 years ago.

Top Image: Elephant seals, Mirounga angustirostris, gather at The Piedras Blancas rookery on the California coast. (Leigh Vogel/Corbis)