Robert Zubrin (NRO) argues that, contrary to conventional wisdom, increasing levels of atmospheric carbon dioxide is beneficial for the environment.
By enriching the carbon-dioxide content of the atmosphere from its impoverished pre-industrial levels, human beings have increased the productivity of the entire biosphere — so much so that roughly one out of every seven living things on the planet owes its existence to the marvelous improvement in nature that humans have effected. Through our CO2 emissions we are making the earth a more fertile world.
...There is no reason to fear a more clement climate. A thousand years ago, the world was significantly warmer than it is today. A thousand years ago, the snow line in the Rockies was a thousand feet higher than it is now, and Canadian forests flourished tens of kilometers farther north. A thousand years ago, oats and barley were grown in Iceland, wheat in Norway, hay in Greenland, and the vineyards of England produced fine wines as far north as York. These warm temperatures were no disaster. On the contrary, persisting through the twelfth century, they are believed by historians to have contributed materially to the significant growth of population and prosperity in Europe during the High Middle Ages (roughly the years 1000 to 1300).
...During the 1970s, the earth experienced a short-term cooling trend, and as a result many of the current cast of global-warming alarmists then predicted an icy doom unless human industrial and population expansion (which they blamed for the phenomenon) could be brought under strict control. This history has exposed them to some mockery, but in fact their previous stand was more to their credit. The global-cooling doomsayers of the 1970s may have been wrong, but at least they were yelling about something that, had it been real, would have been bad. Global cooling would indeed have been a disaster, leading to a drier, more sterile planet. Had the threat of another ice age actually been valid, a forceful government effort to avert such a catastrophe might well have been justified. But as the blame for global cooling could not be conclusively assigned to humanity, the case held little of enduring interest to humanity’s prosecutors.