Global warming is the warming near the earth's surface those results when the earth's atmosphere traps the sun's heat. The earth is getting warmer. The changes are small, so far, but they are expected to grow and speed up. Within the next fifty to one hundred years, the earth may be hotter than it has been in the past million years. As oceans warm and glaciers melt, land and cities along coasts may be flooded. Heat and drought may cause forests to die and food crops to fail. Global warming will affect weather everywhere, plants and animals everywhere, people everywhere; humans are warming the earth's atmosphere by burning fuels, cutting down forest, and by taking part in other activities that release certain heat trapping gases into the air.
One major cause of global warming is the use of fossil fuels. Fossil fuels like coal, oil, and natural gas that were formed from the remains of plant material deposited during the earth's carboniferous period. We have known for only a few thousand years that coal, oil, and natural gas can be burned to provide energy. It was not until the mid-1800s, however, that we began to burn very large quantities of these fossil fuels. The worldwide consumption of fossil fuel has increased dramat.
Unfortunately, burning fossil fuels is not the only thing that we humans are doing to increase the amount of carbon dioxide in the atmosphere. In many parts of the world today, forests are being destroyed at an alarming rate. Enormous numbers of trees are being cut down, both to provide timber and to clear the land for farming or ranching. This destructive process is called deforestation. In order to clear forests for agriculture, people cut down and burn all the trees in area. When the flames die down, nothing is left but acres of blackened, lifeless countryside. The fire destroys all the plants and kills or drives off the animals. Because there has been little attempt to replant trees in deforested areas, the world's forests are disappearing very quickly.
If we can reduce the greenhouse gases going into the atmosphere, we probably can slow the rate of global warming and climate. There are a number of things that we can do to prepare for the changes that are coming. If we act now, perhaps we can "soften the blow" of the greenhouse effect. In the future, the weather cold change much more dramatically from year to year than it does now. As global warming alters habitats, many kinds of animals will be on the move, but all sorts of barriers will stand between them and a new place to live. To help animals get around these barriers, it might be necessary to set up migration corridors that connect natural areas with one another. Without human intervention, many kinds of plants also may not survive as the earth's climate changes. Forests, in particular, may need our help. If climate changes come rapidly, few tree species will be able to spread into new areas fast enough to keep up with changing conditions.
Glaciers are large, thick masses of slow-moving ice that persist from year to year. They cover about a tenth of the earth's land surface. The vast ice sheets of Antarctica and Greenland account for most of this area. Smaller ice caps are found in Scandinavia, Caffin Island, Iceland, and elsewhere. In addition, there are tons of thousands of valley glaciers that follow stream channels down mountain slopes. All together, glaciers contain about seventy-five percent of the available fresh water of the earth. Because global warming is expected to be greatest in polar and temperate regions, scientists expect the glaciers to melt more rapidly than they do today. An executive summary of a United Stations survey published in 1990 concluded that if worldwide "business as usual" continues, the resulting global temperature increased would produce mean sea-level rise of about twenty-five inches by the end of the next century. Other studies predict such increases will occur as soon as 2040. Much depends on how fast the polar ice melts. If global warming accelerates and the ice melts faster than expected, ocean levels may rise as much as ten feet by 2100.