Global warming research eyes ‘runaway’ ice melt

Sea level forecasts may be way off

Will there be runaway ice sheet melting? Bob Berwyn photo.

By Summit Voice

FRISCO — Most climate models are probably underestimating the rate of sea level rise expected during the next few decades, according to some of the latest research that tries to quantify how much ice may melt off the Greenland and Antarctica ice sheets.

A Dec. 26 update by James Hansen and Makiko Sato warns that melting of those ice sheets could increase sea level rise exponentially higher than most existing forecasts, potentially inundating coastal cities around the world with several feet of water by the end of the century.

The short paper discusses the linearity assumptions in most existing climate models and suggests that, if greenhouse gas emissions continue unchecked, “the climate forcing will be so large that non-linear ice sheet disintegration should be expected and multi- meter sea level rise not only possible but likely.”

The formal climate assessments by the Intergovernmental Panel on Climate Change anticipate a sea level rise of only a few tens of centimeters by the end of the century, with other recent papers suggesting that a rise of about 1 meter is more likely.

In the December update, Hansen and Sato explain that most of the models are based on paleoclimate ice sheet changes, but that those changes were the result of gradual climate forcings over thousands of years — “not by a forcing as large or rapid as human-made forcing this century.”

In a paper pending publication, Hansen and Sato say they will present evidence that even those paleoclimate records don’t support the slow rate of change shown by most ice sheet models.

Some of the most recent data in Greenland ice sheet melting suggest that Greenland’s ice alone could cause sea level to rise by about 30 centimeters by 2100. If that rate of melt were to double every 10 years, sea level could rise by 5 meters by 2090.

At some point, though, that rapid melting would trigger a negative feedback loop, with regional cooling of oceans that would slow sea level rise — but not before the oceans swallow up almost inconceivable chunks of coastline.

The West Antarctic Ice Sheet may also be prone to a super-sized meltdown in the next few decades, but for now, it’s too early to tell if ice loss will be exponential. Data from the next few years may tell that story, but Hansen and Sato conclude that, by then, it may be too late to avert massive sea level rise:

“Obviously we need to continue to monitor the ice sheets as well as practical, especially with the gravity and input-output methods, which appear to be the most promising. Also, given the fact that we could reduce the dangers of climate change greatly by putting an honest, gradually rising price on carbon emissions, and there would be many other merits of doing that, it would make good sense to slow down the climate change experiment by placing such a fee on carbon.”


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