Sea Level Rising

The Intergovernmental Panel on Climate Change estimates that — on average, in the past century — sea level rose 10 to 25 centimeters — that’s 4 to 10 inches.

Scientists agree that sea level has been rising since Earth’s climate began to warm at the end of the last ice age. But the rate of sea level rise appears to be increasing. The Intergovernmental Panel on Climate Change estimates that it rose 10 to 25 centimeters — 4 to 10 inches — in the last century. They predict it’ll rise twice as fast in the coming century. There are several mechanisms that cause sea level to rise. One is that, as the ocean gets warmer, water expands. Keith Echelmeyer at the University of Alaska talked with us about another contributor to sea level rise — melting glaciers in Alaska.

Keith Echelmeyer: There’s two main things. There’s the fact that the glaciers are thinning, and that says that the climate is changing. There’s just no way it cannot. The other one is that here are some glaciers which aren’t that big, in terms of all the glaciers in the world or all the ice in the world, but they are such active glaciers in terms of how much snowfall you get up high, and how much melting you get down low, that they are contributing a large part of the rise in sea level.

How large? Echelmeyer’s study of 100 glaciers in Alaska suggest that Alaskan glaciers contribute about 10 percent to overall sea level rise.

The contribution of melting glaciers

Alaska has more than 1000 glaciers — and Echelmeyer and his team have only studied about 100 of them. They studied 100 (or so) glaciers in many different areas and environments in Alaska, so that they’d be able to draw conclusions about glaciers in other parts of the state.

Here’s the team’s game plan: By flying aircraft over glaciers and shooting a laser beam at the ice’s surface, the research team was able to make measurements of the amount of ice contained in the glacier — and keep track of certain glaciers from year to year. The team was also able to compare their laser-built maps of glacier volume, with maps made in the 1950’s by the USGS.

Both the 10 year time series and the USGS maps suggest that the majority of Alaskan glaciers are shrinking. (Some of the ones that are growing are tidal glaciers — explains Echelmeyer. What causes tidal glaciers – that is, ice sheets that dip their toes in the sea — to grow and shrink is not well understood.)

Echelmeyer and team calculated the amount of ice lost from the glaciers they studied — and then entered this information into a model, which estimated the amount lost from all the glaciers in Alaska based on the information they had. Now the team had the amount of melted ice. The next step was to take satellite estimates of global sea level — and divide to get the amount of sea level rise.

Keith Echelmeyer: The changes in these glaciers are due to climate change, that’s what they have to be , there’s some sort of climate change going on.

That climate change could be due to an increase in temperature. The team is making measurements of temperature on some glaciers. But the change could also be du e to an increase of rain and snowfall in the winter. This extra snowfall in the winter could translate into more run-off from the glaciers in the summer.

Alaska’s climate is milder than that of the polar regions — which aren’t thought to contribute as much to sea level changes. The glaciers receive more rain and snow there in the winter — and consequently more water from melting in the summer.

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