The best science indicates that to stabilize the climate, we must rapidly reduce human greenhouse emissions on the order of 70 percent. This is a huge task, but the longer we wait, the bigger the challenge when we finally get to it. Because the climate resembles a speeding train that takes a long time to slow, the longer we wait the greater the risk that we will set in motion natural forces we cannot stop. There are huge risks in waiting too long. The greenhouse effect could feed the greenhouse effect by unlocking huge amounts of greenhouse gases from natural ecosystems. The loss of tropical rainforests to drying and fires would release massive amounts of greenhouse gases, as would melting of Arctic tundras and heating of seabed sediments. Ironically, global warming could send the Earth back into the ice age by shutting off the Gulf Stream to the North Atlantic, which carries tropical heat north and keeps Europe 15 deg. F warmer than it would otherwise.
Global warming is a train that is speeding up right now. First we need to slow the train, and then we need to stop it. We can do so by transforming our energy system from one based on fossil fuels to one based on natural, renewable energies including sun, wind, tides, plant growth and geothermal energy. We have the technology, but applying it will take a large investment by government and business. In shifting to clean energy, we will also eliminate much air pollution, and build new industries and a new basis of sustainable prosperity. If we move quickly to clean energy, stop deforesting the tropics and move to more sustainable agriculture, we will eliminate most greenhouse gases, and avert climatic catastrophe. This is one of the largest challenges humans have ever faced, but we are richer now in economy, technology and scientific knowledge than we ever have been before. We are well up to the task. We just have to recognize its critical importance to our future.