In the process known as photosynthesis plants use the sun's energy to produce food. During this process, plants release oxygen and absorb carbon. All the tropical rainforests of the world together produce 50% of the world's oxygen. One can image the astronomical amounts of carbon that would be released into the atmosphere if the rainforests were destroyed.
Furthermore, as the rates of carbon dioxide (CO2) increase, so do the carbon monoxide (CO) rates. The burning of forest vegetation is a major factor in the increase of CO. In fact the largest single source of CO2 is a result of the "slash-and-burn" fires in the Amazon, which alone produce 17% of the world's CO2. However, as the rainforests are burnt down, the increase in CO is not limited to the areas of deforestation, but occurs in equal amounts all around the world. This means that even people who live thousands of miles away from the tropical rainforests, still experience the same increase in CO2.
If CO levels continue to rise with increasing speed, future generations can expect to find global smogs of unprecedented density, where once clear blue skies were. Increasing concentrations of greenhouse gases (which include CO2, CO, and other gases) pose another threat: the increase of global temperatures. Over the last century, the 1980s have had the five warmest years (based on 1990s annual temperatures). At the current rate of deforestation, many parts of the globe may experience an increase of several degrees in a matter of only decades.