First, there is the fact that tropical rainforests contain an extraordinary diversity of life, both plant and animal. The destruction of the rainforests would wipe out most of these life forms. Furthermore, because trees absorb carbon dioxide, deforestation means that less of this greenhouse gas would be removed from the atmosphere, a situation that contributes to the greenhouse effect and therefore global warming.
Conversely, the forests also emit large quantities of oxygen, which is important for obvious reasons. There is also the fact that rainforests absorb large quantities of rain, helping to avert flooding in lowlands around the forests. Finally, rainforests obviously contain a great deal of valuable resources, including wood and other plant products such as nuts, fruit, and medicinal plants and herbs. For these reasons, the estimates, given by many scientists, that around half of the world's old-growth rainforests have been wiped out should be viewed as a global emergency.