In other words, from any rational point of view, global warming would be a very good thing. 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).
If we wish to look at a longer span of the earth’s history, average global temperatures can be estimated by examining sea-floor material. Looking at the data
, we see significant global cooling since the time of the Paleocene-Eocene Thermal Maximum (PETM), which occurred 55 million years ago. The atmosphere contained 2,000 parts per million carbon dioxide, more than five times the 380 parts per million that is does today. New species of plants evolved that were capable of using carbon dioxide more efficiently. The most important of these were the grasses, which, originating at the end of the Paleocene about 58 million years ago, drove temperatures sharply down. Things then stabilized in the Oligocene, until the mid-Miocene, about 15 million years ago, when additional types of grasses appeared. These more advanced grasses were much more efficient at carbon-dioxide utilization, and as they replaced their predecessors, they drove atmospheric carbon-dioxide levels below 300 parts per million for the first time in the earth’s history. In the process, they sent the planet’s climate plunging into a glacial age that has continued to the present day.
Twenty million years ago, vast regions of what are today frozen polar deserts in the Arctic and Antarctic were forests, inhabited by vibrant communities of animal life. Today these regions are close to dead, made uninhabitable by the failure of the wild biosphere to maintain sufficient levels of atmospheric CO2.
The fact that the earth’s atmospheric carbon-dioxide concentration was about 280 parts per million shortly before the industrial revolution implies that this value is close to the minimum acceptable equilibrium level for the modern biosphere. As human industrial activity pushes carbon-dioxide levels above this impoverished state, we increase plant productivity, causing the biosphere to push back like a spring, with the force of its push becoming ever stronger the further the system is displaced from equilibrium. The more fossil fuels we burn, the more carbon resources we make available for plant growth, and the more productive the biosphere becomes.