Everyone is concerned about the environment and most everyone wants to do their part to help. We can keep streams free of pollution, plant trees, recycle and do many other things to help the environment. One big problem, however, is with "carbon dioxide" - a gas that we cannot see or smell but that is being put into the air by cars, factories and power plants. This gas and some of its relatives are called greenhouse gases because there is a chance that these gases could end up warming the Earth just like a greenhouse. If this happens, farmers might not get enough rain for their crops in some places while others might be flooded all the time.

Scientists around the world are now busy studying just how big a problem these greenhouse gases will cause. To do this, they use computers that try to forecast not just the weather tomorrow but in 20 years as well. This is not easy. The biggest problem is that scientists don't really know what the normal weather is around the world. While the world has experienced more droughts and floods recently, scientists are still not sure if the world is starting to feel the effects of these greenhouse gases or if these droughts and floods are normal.

To help scientists, NASA is launching a set of satellites in a program called Mission to Planet Earth. One of the first satellites launched was the "Tropical Rainfall Measuring Mission" or TRMM for short. Its mission is to measure the rainfall all around the tropics where most of the world's rain falls. These measurements include the large ocean areas where very little is known about the rain. By studying these measurements, scientists will be able to know what the normal rainfall is and maybe what the normal changes are from one year to the next. The TRMM satellite by itself will probably not answer all the questions by itself. Together with other satellites in NASA's Mission to Planet Earth, however, scientists hope to learn enough about the weather to make predictions about the weather in 20 years so that they can better understand just how big a problem these greenhouse gases really are.