Warmer May Mean Bigger for Coastal Glaciers
Headlines, commentaries, and even this column have been crowded recently with words of worry about the greenhouse effect, the apparently inevitable warming of Earth's atmosphere because human activity continues to change the balance of the gases in the air we breathe.
When it comes to what this really means for Alaska, it's possible to find almost as many opinions as there are knowledgeable scientists. One of the oddest probabilities is that a warmer climate could set our coastal glaciers growing. And yes, there is some evidence that this has started to happen.
To explain this apparently unreasonable behavior, it's necessary to examine why the glaciers grow where they do along Alaska's southeastern and southcentral coasts. First, consider the scenery: a complex seacoast backed by steep mountains. Next, remember that glacier ice starts as compacted snow--snow that falls high in the mountains, so thickly that summer's heat can't melt it away. The next winter's snowfall descends upon the remains of the previous winter's snowpack, compressing it eventually into ice. Over years, decades, centuries, the ice builds. Pulled by gravity, finally a glacier flows downhill. Its tongue may reach the sea, but its tail remains in the mountains, fed by the highland snows.
Now, return to the cause of the soggy weather along those coasts. Wet air comes off the North Pacific Ocean. The air mass is comparatively warm, and warm air can hold more moisture than cold air. The oceanic air holds so much moisture that just a little cooling is all it needs to start dumping water. The air's lifting as it encounters the coastline can produce enough cooling to do that. Thus Juneau, Yakutat, and Valdez are deservedly known as rainy places.
The water that doesn't rain out accompanies the air uphill into the colder zones high on the mountain slopes. The air chills more, and must release more water. If it's cold enough, the precipitation will fall as snow.
If the sea water and the air above it are warmer, can it be that more moisture will make its way uphill, high enough to fall as snow to feed the glaciers?
Larry Mayo and Dennis Trabant, researchers with the U.S. Geological Survey in Fairbanks, have documented exactly this happening on Wolverine Glacier near Seward. For several years, they have studied what glaciologists call the "mass balance" of the Wolverine--the comparison among the amounts of glacier material that melts, evaporates directly, and accumulates annually. Their measurements show that the Wolverine is growing, while the nearby weather has been a bit warmer than usual.
Most of the added warmth has come in the winter. That means a good bit more snow has fallen on the upper reaches of the glacier, while the summers have not been warm enough to melt the additional snow.
The glacier's growth isn't obvious. Its terminus is still receding, because it takes a long time for the lower reaches of a glacier to react to what happens above. Its meltwater runoff has increased, but the U.S.G.S. scientists say that the measured precipitation on the Wolverine is so much heavier that lots of it is left to increase the volume of ice. Their numbers are clear: more snow falls on Wolverine, the glacier contains more ice, and the winters are warmer.
Equally clear are measurements showing that the water in the Gulf of Alaska is a bit warmer, and that the onshore flows of moist air are more forceful than they were.
The scientists are not predicting that warmer weather certainly will produce fat, advancing glaciers everywhere in Alaska's coastal mountains. Alaska has more glaciers than glaciologists, so not all our rivers of ice can be studied with the attention given Wolverine Glacier. Changing climate could continue to alter oceanic and atmospheric patterns, and such changes could alter the precipitation patterns that feed the glaciers.
Still, by reasonable theory and by partial evidence, the odds are good. It seems illogical, but if the appropriate parts of Alaska enjoy warmer winters, their glaciers will grow bigger.
