The Island of Doubt

Sixty years is a blink of the metaphorical eye on geological time scales, and it's still damn fast when you're talking about climate change. While it may be far too long for Wall Street to worry about, six decades is safely with human lifespans, and a study that concludes temperatures in Greenland can shift by 18 degrees Fahrenheit (10°C) in such a short time merits more than a passing mention.

We've known for a few years now that regional climate patterns can shift dramatically with a decade or two, but precise details have been hard to come by, primarily because we just didn't have the technology to resolve the paleoclimatic data found in ice cores. Each layer gets thinner and thinner the further back in time you go. But the new paper, "High-Resolution Greenland Ice Core Data Show Abrupt Climate Change Happens in Few Year" (Science Express, 10.1126/science.1157707) by an international team lead by J. P. Steffensen of the Centre for Ice and Climate at the University of Copenhagen, takes advantage of "unparalleled temporal resolution and continuity" and gives us some incredible first looks at just how fast things can change.

Seems there were a couple of big changes as the Earth was coming out of the last ice age, changes that saw a rapid warming, then cooling, then another fast warming period. It was all happening about 15,000 to 11,000 years ago. According to Steffensen et al, their analysis of North Greenland Ice Core Project data suggest that the

"...warming transition at 14.7 ka b2k, is the most rapid and occurs within a remarkable 3 years while the warming transition at 11.7 ka b2k lasts 60 years; both correspond to warming of more than 10K."

Looking at the various proxies for temperature —precipitation levels surmised from oxygen isotope and deuterium ratios and such — they conclude that the swings are caused by melting ice packs and sheets, but are more likely due to "a reorganisation of atmospheric circulation from one year to the next."

This reorganisation of the tropical atmospheric circulation is followed by a complete reorganisation of the mid to high-latitude atmospheric circulation almost from one year to the next, as identified by the 1-3 year transitions in deuterium excess.

The high resolution records from the NGRIP ice core reveals that polar atmospheric circulation can shift in 1-3 years resulting in decadal to centennial scale changes from cold stadials to warm interstadials/interglacials associated with astounding Greenland temperature changes of 10K. Neither the magnitude of such shifts nor their abruptnesses are currently captured by state of the art climate models.

Why should we care? Because the way heat is distributed around the planet, Greenland won't be the only place experiencing dramatic warming. Warming that lasts more than a 1,000 years. Warming that can shut down the thermohaline conveyor (of which the Gulf Stream is part). Warming that can mean droughts that would essentially wipe out agriculture everywhere.

This study is important, and deserves more attention than it's getting because it's hard data on what can actually happen. It's not "just a model." And it shows that it is possible to see catastrophic climate change within a single human's life.

What does this study not do? It doesn't tell us why the changes happened and why they happened as fast. Blaming the temperature swings on changes in atmospheric circulation is only pushing back the question one step. We have theories, but no real solid answers.

But we do know that there is more than one way to push the Earth's climate between equilibria. And increasing the levels of heat-trapping greenhouse gases is almost certainly one of them. The most recent big shifts in temperature probably weren't caused by rising CO2 levels, but once the gases start rising, they can take over as the prime mover of future temperature rise.

And that's why this study scares me. And why it should scare you.

Steffensen, J.P., Andersen, K.K., Bigler, M., Clausen, H.B., Dahl-Jensen, D., Fischer, H., Goto-Azuma, K., Hansson, M., Johnsen, S.J., Jouzel, J., Masson-Delmotte, V., Popp, T., Rasmussen, S.O., Rothlisberger, R., Ruth, U., Stauffer, B., Siggaard-Andersen, M., Sveinbjornsdottir, A.E., Svensson, A., White, J.W. (2008). High-Resolution Greenland Ice Core Data Show Abrupt Climate Change Happens in Few Years. Science DOI: 10.1126/science.1157707