Global warming. Computer-generated images of the world showing the projected spread of drought up to the year 2050. Brown and orange indicate regions with a high probability of drought. The projection was made by the Global Climate Model of NASA's Goddard Institute for Space Studies on the basis that the emission of "greenhouse" gases (such as carbon dioxide, methane and CFCs) will continue to grow at current rates. These gases trap an increased amount of solar radiation in the atmosphere, leading to gradual warming of the planet. Global Climate Models use available data to model Earth's climate using supercomputers.