Lots of climate-change studies, still few certainties

The Arctic can be frustrating for scientists trying to predict global warming.

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    Icebergs float in a bay off Ammassalik Island, Greenland.
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The Arctic can be frustrating for scientists trying to predict climate change. They know Arctic climate is changing faster than expected. Yet they don’t understand what’s happening today well enough to trust computer projections of what may happen there tomorrow. Two weeks ago, Nature published a review of this challenge, featuring Greenland’s situation. It concluded that lack of a full-court press to understand what’s happening in the Arctic today “could turn out to be one of the most short-sighted allocations of [climate research] resources.”

Actually, a lot of Arctic research is going on. Halfway through the International Polar “Year” (March 2007 to March 2009), about 60 countries are involved with about 160 projects. Such efforts are rapidly building a patchwork of new knowledge. Yet, as Nature points out, they aren’t a “systematic” learning process. Scientists can’t build computer-based climate models on disparate research that turns up something “totally different” every research season.

The situation in Greenland illustrates this point. Scientists know that the ice flow from Greenland into the sea is speeding up. They have suspected that summer meltwater is draining down beneath the ice and lubricating its flow – therefore accelerating it further.

Some wondered if it could penetrate thousands of feet of rock-hard ice. Research reported two weeks ago online in Science Express supplied the answer. Sarah Das at the Woods Hole Oceanographic Institution, Ian Joughin at the University of Washington, and their colleagues describe how, in 2006, a 2.2-square-mile lake with 11.6 billion gallons of water drained away in 24 hours. Most of it went in 90 minutes. Dr. Das calls this “clear evidence” that summer meltwater pools “can actually drive a crack through the ice sheet” all the way to the bottom. Once there, it can speed up glacial flow by 50 to 100 percent in some broad areas of the ice sheet.

That’s an important discovery. But outflow glaciers on the coast that channel glacial ice to the sea hardly sped up at all in 2006. Something else seems to be at work.

Scientists’ knowledge of ice-flow mechanisms remains too patchy for prime-time climate forecasting.

So, too, is their knowledge of the continuing loss of Arctic Ocean ice cover. Last week, Jennifer Kay at the National Center for Atmospheric Research in Boulder and colleagues explained in Geophysical Research Letters that summer cloud cover has become an important factor in that loss. Cloud cover didn’t matter that much in the past when the ocean was largely ice covered. The ice reflected much of the sunlight back to space.

But now there’s more exposed water to soak up sunshine. The warmer water melts ice from below, thinning it out. Dr. Kay says that “a single unusually clear summer can now have a dramatic impact.” This is one more factor to add to the changes in winds and currents that affect sea ice, the relative importance of which is still unknown.

As Nature said two weeks ago, it will take a systemic well-funded effort by “the entire polar research community” to turn the present patchwork of programs into a pursuit for useful understanding.

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