The ocean plays a particularly important role in moderating climate change. First, the ocean has a higher specific heat than land, which means that its temperature rises more slowly than that of land. Effectively, this means that the ocean slows global warming.

Second, the ocean absorbs carbon from the atmosphere. Thus, much of the carbon dioxide that humans release into the air from burning fossil fuels is absorbed and contained by ocean waters. Again, this means that the ocean slows global warming.

The effectiveness of the ocean in slowing global warming may be reduced over time, however. As water temperatures rise, the ocean becomes less able to absorb carbon dioxide. As global warming accelerates, the ocean will become a less effective brake, which will accelerate global warming further.

This kind of effect—wherein a given phenomenon creates conditions that increase or exacerbate the phenomenon—is called a feedback loop. Scientists are concerned about a number of feedback loops involving water and ice.

One of the most important of these phenomena is a water vapor feedback loop. Water vapor is itself a greenhouse gas; that is, more water vapor in the atmosphere tends to trap heat on the earth and raise temperatures. As temperatures go up, more water on the earth evaporates, becoming water vapor and going into the atmosphere—where it raises temperatures. Scientists are not sure, however, how important this effect will be in the long term. In part, they are uncertain because more water vapor in the atmosphere might also mean more cloud cover, which would reflect sunlight and cool the earth.

Another potentially important feedback loop involves ice albedo. Albedo is the ability of a substance or body to reflect sunlight. Ice has a very high albedo; ocean water has a much lower albedo. Scientists worry that, as temperatures rise worldwide, ice may melt. With less ice, more ocean water will be exposed. That means that the overall albedo of the ocean will fall, and the ocean will absorb more heat faster—possibly raising the temperature of the water further and melting more ice.

0 0

Post a comment