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Warming? What Warming? 'Leveling Off' Explained

October 23, 2013

Mystery of the 'Missing' Global Warming

Smokestacks and cooling towers from a coal-fired power station near Bergheim, Germany. Photographer: Wolfgang von Brauchitsch/Bloomberg

Have you heard the one about how global warming stopped in 1998? It’s been called a “pause,” a “hiatus,” a “slowdown” and a “siesta.” Above all, it’s a red herring, and it isn’t difficult to find where some of the ‘missing’ heat has gone.

First, in case you haven’t been paying attention: 97 percent of climate scientists agree about global warming and its man-made causes, now with 95 percent certainty, according to a report this month by the IPCC, the world’s most authoritative body of climate scientists. Greenhouse gases trap heat, which melts ice, raises seas and floods cities; this fundamental equation is not in doubt.

What has raised a few eyebrows recently is that temperatures on the surface of Earth have increased at a slower rate since 1998 than in previous decades. Scientists have largely chalked this up to the short-term variability of climate. However, climate skeptics have taken the surface-temp slowdown acknowledged by the IPCC to mean that global warming itself has stopped -- that somehow the physics has changed.

It hasn’t.

“The planet is warming,” said Kevin Trenberth, a senior scientist at the National Center for Atmospheric Research and a reviewer for the IPCC report. “The warmth just isn’t being manifested at the surface.”

The chart below, from the U.S. National Oceanic and Atmospheric Administration (NOAA), shows what’s going on beneath the surface. The red line shows a half-century of temperatures for the first 700 meters of ocean water below the surface; the black line shows temperatures of waters to a depth of 2000.

[imgviz image_id:isp5qCVylj7o]

The warming at the ocean’s surface layer may have slowed a bit, but ocean temperatures in aggregate have continued to rise unchecked during the so-called hiatus, according to the IPCC. That’s important because while the atmosphere accounts for just 1 percent of planetary heat, the oceans carry 93% of the stored energy from climate change (melting ice and warming continents make up the rest).

In fact, there is mounting evidence that deeper regions of the ocean, down to 2000 meters, are absorbing heat faster than ever, Trenberth said in a phone call. His research shows the oceans began taking on significantly more heat at around the same time the surface warming began to slow in 1998. His widely cited work was published just after the cutoff to be included in the IPCC report.

The irony, says Trenberth, is that when the surface of the planet is unusually sweltering, the Earth actually radiates more heat into the atmosphere, in effect slowing the long-term warming of the planet. And in “hiatus” years, when the surface is cooler, the Earth absorbs more of the sun’s heat deep the oceans, slowly cooking the planet. What you see isn't always what you get.

Ocean temperatures are just one of many independent lines of evidence showing that climate change continues to speed ahead on an alarming course. Need more? Look to the seas that are rising faster than previously anticipated, the imbalance of energy measured entering and exiting the upper atmosphere, and the melting glaciers and permafrost. I could go on.

But the next time you’re at a barbecue and someone tries to tell you global warming stopped in 1998, just throw some cold (ocean) water on the debate. And don’t sell your getaway ark just yet.

Read the full IPCC report here. Warning: It’s 2,200 pages and not for the scientifically faint of heart. The more digestible 30-page summary for policy makers is available here.

More by Tom Randall:

  • Look Who Out-Guzzles the U.S. at the Fuel Pump
  • Cricket Eaters Invest Like Buffett at SXSW Eco
  • ‘Peak Fossil Fuels’ Is Closer Than You Think
  • Kansas's Self-Destruct Button: A Bill to Outlaw Sustainability

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