This is a very important question! Global warming may have significant impacts on our environment over the next century, and many say that it is currently responsible for changes in weather and climate patterns already. The short-term variability of the weather makes it very hard to base decisions on only a few years’ observations, but the long-term trends (measurements over a hundred years) do indicate that we are on a warming trend.
Changing the average temperature on the Earth by even a few degrees is enough to upset delicate climate patterns. How these patterns are upset and by how much and how long it takes are matters we do not know for certain, but we do have ranges of predictions. We expect that even a small increase in the average temperature will melt large amounts of ice near the poles.
Much of this ice is in contact with water. At the South pole, gigantic ice shelves float on water, and at the North pole, there is no land and the ice floats on water. Much of the ice has a temperature very close to that of the nearby water, and so is ready to melt. There is a steady-state situation where snow falls around the poles, packs into ice, flows down in glaciers, and melts in the sea -- this process is extremely slow. Increasing the water temperature will increase the heat flow rate into the melting process, and reduce the equilibrium amount of ice at the poles.
Today there was an interesting item
on CNN’s website which claims that the snowfall rate on the poles may actually increase as the Earth warms. The argument is that with higher temperatures comes more evaporation of water from the oceans, and this must fall as precipitation somewhere, and that some of that precipitation increase may be found as snow near the poles.
This may not be enough to increase the amount of ice and snow around the poles. Most glaciers around the world have shrunk over the last century, even if the precipitation rate has gone up in some places. The precipitation rate may even go down in some places (like areas that are already deserts).
One question you may also be wondering about is how the melting ice caps would affect the sea level. When you melt an ice cube in a glass, the water level doesn’t change. However, the South Pole ice and the Greenland ice are not floating but sitting on land. As they melt, the sea level will rise. The sea level would also rise as the ocean temperature goes up, because most of the ocean is at temperatures for which water expands when it warms.
(published on 10/22/2007)