Scientists recently scrambled to correct a wildly exaggerated estimate of how fast Greenland's ice cover is melting. Although climate denialists often claim that we climate scientists are too politically biased to be objective about climate change, this example shows that our professional code leads us to challenge factual errors regardless of who makes them. Errors of omission are also common in public discussions of climate change, though they are less often addressed by scientists. For example, widespread melting is generally thought to imply imminent collapse of the entire ice sheet. In reality, however, a total greening of Greenland would take longer than most of us realize.
We care about such a melt-off because it's shocking to imagine the place without ice, and especially because such melting could raise sea levels by more than 20 vertical feet (Antarctic ice could add another 200 feet to that total). Considering the mineral wealth hidden in the now-glaciated bedrock, the potential for much-needed local agriculture, and the opening of ocean shipping lanes and marine resources, a demise of the great ice sheet could yield important local benefits as well as losses. On the other hand, sea level rise is a global-scale problem with little to no benefits, and it underlies most concerns about the great Greenlandic thaw.
Few of us seem to recognize that the melting rate is only meaningful if we also consider how large the ice sheet is. Just as spending a million dollars on some project can seem unimaginable for a small village but easy for a large nation, describing how much water leaks from Greenland's shrinking flanks means little unless you also know how big the ice sheet is. What we don't often hear is what a surprisingly huge lot of ice there is to melt.
Recent measurements show that there's enough ice in Greenland to build a symmetrical cube measuring roughly 90 miles on a side. It could fill nearly 700,000 cubic miles of volume-space and it covers an area three times the size of Texas. Even with huge torrents of meltwater running into the sea each year, it would take a long time to lose that much ice entirely.
Computer simulations of complex deglacial melting and surging processes are still too primitive to be very reliable, but even the extreme projections require many centuries to do the deed. Most scenarios stretch the thaw over several millennia, depending on how warm it gets; some take as much as 20,000 years.
Another way to estimate the durability of Greenland's ice is to look to the distant past. Ice cores and marine sediments show that dozens of cyclic natural warmings have punctuated the last 2 to 3 million years without totally deglaciating the poles. The one before the last ice age, the Eemian Interglacial, kept Arctic summers several degrees warmer than now between 130,000 and 117,000 years ago, but at least half of Greenland remained glaciated even after 13,000 years of Eemian heating.
Is it wrong for a climate scientist to point this out? Some would say so, and my description of this subject elsewhere led one environmentalist-critic to conclude; "I shudder to think how Rush Limbaugh might interpret this book." But good scientists favor truth over ideology, and the reality of human-driven climate change is plenty serious enough that it requires no exaggeration.
Recognizing the relatively slow pace of the Greenlandic meltdown need not justify complacency, even if the panic-response to imaginary violent melt-flooding is unwarranted. No nation would relinquish even the thinnest strips of its borderlands to another country without a struggle or much compensation, and even slow sea level incursions are well worth avoiding as much as possible.
Despite the relatively slow pace of polar deglaciation, the choice we face today remains clear. If we switch to non-fossil fuels within the next several decades, a fair bit of Arctic ice will likely survive, perhaps along with polar bears and other ice-dependent species. But if we blaze through our remaining fossil fuel reserves, we'll de-ice the polar regions, submerge huge stretches of coast, and cover low-lying islands for thousands of years to come.
[Image: Flickr user christine zenino]
Curt Stager is an ecologist, paleoclimatologist, and science journalist with a PhD in biology and geology from Duke University. His new book is DEEP FUTURE: The Next 100,000 Years of Life on Earth (St. Martin's Press, March 2011).