Sea Level Update:
For the final blog entry of 2008, I wrote about what I thought would be the important science questions that needed to be addressed by climate change science in the next four years. In that blog
I had at the top of the list the melting of land ice was probably underestimated, and hence, sea level rise was underestimated.
Sea level rise comes from both the warming on the sea water and the addition of water to the ocean from melting ice on the land. Looking into the future, the pressing question is what will happen to the ice sheets in Greenland and Antarctica. In general this discussion divides the land ice into three parts, Greenland, West Antarctica and East Antarctica. The volume of water in Greenland is equal to about 6-7 meters of sea level rise. West Antarctica is about 5 meters and East Antarctica about 65 meters. The good news is that East Antarctica is the most stable of these ice sheets.
As we learn more about how ice melts
we find two pieces of news. The first is that as we reveal on a mechanistic level the melting processes, these processes all tell us ice melts more rapidly and more complexly than say an ice cube sitting in a warm room. As ice forms water and the water flows through the ice, the water carries heat and accelerates melting relative to the effects of air alone. The second thing we have learned is that without contact with sea water, the melting of land ice still takes a very long time. Hence, we, or at least I, have more and more reason to believe that we will not
suddenly see 5 or 10 meters of sea level rise.
Last week there was a meeting in Copenhagen, International Scientific Congress on Climate Change
. This was one of several meetings leading up to the Conference of the Parties 15, Dec 7 – Dec 18, 2009
At the Scientific Congress last week there was an update on sea level rise. Here is the press release
. The observations of sea level rise remain at more than 3 millimeters per year, which is the rate observed in the final decade of the 1990s. This rate is higher than the average for the 20th century as a whole. Simple multiplication of this rate for 100 years gives an estimate of 300 millimeters, or 30 centimeters, about a third of meter, about one foot. This amount is in the middle of the IPCC projections.
As noted above, the new knowledge of how land ice melts suggest that we have both underestimated the rate of melt and that total collapse of an ice sheet, say 5 meters of sea level rise, is unlikely. With this the experts who study ice melting and sea level rise are saying, with confidence, that the IPCC projections are lower limits. Currently, researchers are converging on a number on the order of one meter as the amount of sea level rise to expect in the next hundred years. This will have significant impact, as with storm surges, it opens up much more land (and cities) to additional flooding. One hundred year floods are likely to become 10 year floods or perhaps 1 year floods.
It is important to understand that much of this sea level rise is already “built into the system.” That is, the amount of warming that we are already committed to will lead to sea level rise. On a time scale of about 100 years, if we were to reduce substantively our greenhouse gas emissions we could have a mitigating effect on sea level rise. However, as reported at the International Scientific Congress on Climate Change
and many other places, our emission rates currently exceed the “business as usual” scenario of the IPCC. ( Key Messages
Some Icy Blogs Learning about Land IceWarm SnowFast IceThe End of Ice?Vanity Alert … excess vanity alert
A few years ago I lived in Maryland and wrote, perhaps, an essay on learning from the mistakes of forecasts. I sold this essay to the Bay Weekly
. They were saving it until there was a snow storm in Washington, D.C. It’s been years, but it was published the week before last. Lessons of the Storm