Hottest Decade on Record Would Have Been Even Hotter But for Deep Oceans — Accelerated Warming May Be On Its Way

The last decade was easily the hottest on record. We’ve known that sulfate aerosols (from volcanoes and/or Chinese coal) and the “the deepest solar minimum in nearly a century” masked the rate of warming somewhat.

Even so, NASA’s Goddard Institute for Space Studies (GISS), which probably has the best of the long temperature datasets, reported the 12-month running mean global temperature reached a new record in 2010. As a NASA analysis found: “We conclude that global temperature continued to rise rapidly in the past decade” and “there has been no reduction in the global warming trend of 0.15-0.20°C/decade that began in the late 1970s.”

But other datasets appeared to show a slight slowing in the rate of warming, though even that may have been due to flawed data, as in the case of the UK’s Hadley Center.

Scientists have long known that the overwhelming majority of human-caused warming was expected to go into the oceans (see figure below). And many have suspected that deep ocean warming has also been masking surface warming.

Now a new study led by led by the National Center for Atmospheric Research (NCAR) finds that may indeed be the case:

The planet’s deep oceans at times may absorb enough heat to flatten the rate of global warming for periods of as long as a decade even in the midst of longer-term warming….

The study, based on computer simulations of global climate, points to ocean layers deeper than 1,000 feet (300 meters) as the main location of the “missing heat” during periods such as the past decade when global air temperatures showed little trend. The findings also suggest that several more intervals like this can be expected over the next century, even as the trend toward overall warming continues….

“This study suggests the missing energy has indeed been buried in the ocean,” [coauthor Kevin] Trenberth says. “The heat has not disappeared, and so it cannot be ignored. It must have consequences.”

These potential consequences include accelerated warming in the coming decade and melting of the West Antarctic Ice Sheet. Let’s take these two in order.

The heat may have been carried deep into the ocean by overturning circulations, which can plunge surface water from the subtropical regions into the ocean’s depths. The burying of warmer water also corresponds with La Nina weather patterns, which are born from cooler-than-average surface water temperatures in the tropical Pacific. And over the last decade, La Nina conditions have dominated, Trenberth said.

That the heat is buried in the ocean, and not lost into space, is troublesome, Trenberth said, since the heat energy isn’t likely to stay in the ocean forever, perhaps releasing back into the atmosphere during a strong El Nino, when sea surface temperatures in the tropical Pacific are warmer than average.

“It can come back quite fast,” he said. “The energy is not lost, and it can come back to haunt us, so to speak, in the future.”

I asked Trenberth whether we might see a decade where warming is a tad faster than expected, and he emailed me, “Yes.” Once the decade of slower warming “is over, the subsequent warming can play catchup.”

more at link...