Our atmosphere keeps the earth's temperature stable. It lets just the right amount of sunlight through so the earth doesn't get too hot in the summer. It also keeps warmth from escaping so we don't get too cold in the winter. In this way the atmosphere acts like a greenhouse. This is called the “greenhouse effect.” It is part of what makes our planet the comfortable place that it is.

Lately scientists have been worried that too many “greenhouse gases” are building up in our atmosphere. Humans are driving more cars and heating more homes than ever before. We do this mostly by burning fossil fuels (oil and gasoline) and coal. This burning releases greenhouse gases, like carbon dioxide, into the atmosphere. At the same time we are cutting down trees in record numbers. Trees help take up carbon dioxide in the atmosphere and replace it with the oxygen we need. Scientists worry that if we have fewer trees and make more carbon dioxide, we will build up greenhouse gases faster than ever before. This might block even more heat from escaping into space, and like a greenhouse with its windows shut on a hot, sunny day, it might be getting a bit warmer on Earth. This warming effect is called global warming.

Turning Up the Heat

The rise in Earth's temperatures might be just a few degrees, but over time it could have a big effect. Scientists worry that it will eventually cause the polar ice caps to melt and the sea levels to rise. This could change weather patterns and alter habitats in a way that might result in many animals going extinct. It's still early to know all the effects of global warming on our planet, but it's important to know how our actions can make a difference.

Melting Polar Ice Caps

NASA studies Earth from space via satellites. From here they can see changes in the shape and size of the polar ice caps. They can see that the year-round ice pack in the Arctic is shrinking. In the past twenty-five years it has shrunk 10 percent. Scientists have also been watching satellites that have been collecting the earth's surface temperatures for twenty years. They show that the temperatures are rising. In 2003 the largest ice shelf in the Arctic that had been in place for 3,000 years, broke up into the ocean. Climate does change naturally over time, but rapid changes are unusual. These facts may signal global warming.

How would melting ice caps affect the planet? For one thing, the bright white ice caps reflect a lot of the sun's energy back into space. As the ice caps shrink, more sunlight will be absorbed by the earth, warming the climate even more. Melting ice caps would make more water available for the water cycle, which could change the rain patterns and how salty the ocean is around the poles, affecting ocean fisheries.

The shrinking ice shelf is already affecting arctic animal populations. Species like polar bear who hunt seals off ice shelves are unable to find prey as easily without the frozen platforms. Scientists have found that hungry polar bears are drowning while trying to get to prey without the usual ice shelves available to hunt from.