Tuesday, April 15, 2008

Ice is Nice...

Ok, as promised, a (long-winded) post about the arctic and its rapidly dwindling sea ice.

My advisor recently attended a workshop that brought climate modelers and observationalists who study “warm climates” together to talk about that state of the science; his job was to talk about my data related to temperature reconstructions for an extremely warm period of time 55 million years ago. This particular event is used as an analog for modern day global warming, because the time scale of the warming was so rapid ( ~100-200 thousand years in duration). However, geologic metaphors being what they are, this particular event started at a much warmer baseline than at present. In that world, there was no ice at either pole, and this presents a challenge for climate modelers, because models are built upon the climatic relationships we see and understand today.

Anyway, the modelers at work on this problem have historically had trouble getting the models to match the observed data in certain aspects, most notably getting the arctic to warm enough, and the equator to NOT warm so much. For the most part, it is understood that as ice disappears, the role of the ice as a reflector of solar radiation decreases, while the role of the ocean as an absorber of solar radiation increases. As more ice melts, this feedback continues, with decreased sea ice leading to increased rates of warming. This is oversimplified and lacks other feedbacks, but that’s the basic idea. But what happens once you lose the ice?

Back to Paul’s scary anecdote. So, he said, one thing that DOES seem to be coming clear is that arctic warming happens in a step-wise manner. That is to say, something funny happens when we lose all the sea ice. Like most things in life, warming doesn’t happen at a uniform rate; it appears that once the ice goes, a whole lot MORE warming occurs and fast. The more detailed aspects of this are still debated (ie, which feedbacks are most responsible? Is it just sea ice? What role do clouds play? What about the thermal structure and transport of the atmosphere?), but that seems to be the general consensus. And that is a big deal! We really don’t have a good sense for how an ice-free world works. The last time this happened was ~ 35 million years ago.

Ok, so what’s the big deal with that? Melting of the sea ice doesn’t directly raise sea level; it’s hanging out like a big ice cube, and has displaced as much water in solid form as it does in liquid form. And yes, there is some sea level rise predicted strictly from thermal expansion of water as the oceans warm. However, if the rate of warming picks up specifically in the Arctic, the already precarious Greenland Ice sheet will start looking a lot more precarious. And when that puppy slides into the ocean, that’s a lovely 7 meters of sea level rise. And it the sea ice extent decreases sooner than expect, than the Greenland Ice Sheet will likely go earlier than expected as well. Right now, estimates suggest we’ll be ice-free in the arctic sometime between 2060-2080 (again, there are many estimates for this, including earlier dates). That sounds so doomsday, doesn’t it? I’m starting to learn why people who have relatives who are geologists often describe them as crazy…

If you keep track of the global warming/climate change headlines in the news, you’ve probably already heard some aspects of this before. But, we also don’t have all the feedbacks associated with the stability of the Greenland ice sheet nailed down. So, adding together all the things we still don’t understand about sea-ice feedbacks, with all the things we don’t understand about continental ice sheet feedbacks SHOULD make us all nervous that we haven’t made any stronger policy decisions about greenhouse gas emissions, both nationally and internationally. But, it seems to have a strange effect on some people, and they suggest that because we don’t know FOR SURE what will happen, we should just wait. Hmm. You wait. I’m buying some land way north, and away from the beach.

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