Economist.com | Climate change and civilisation

Interesting. Just one more reason to love the hunter-gather lifestyle.

Natural climate change may have started civilisation. And the spread of farming may have caused as much global warming as industry is causing now.

So climate change helped to intensify agriculture, and thus start civilisation. But an equally intriguing idea put forward at the meeting is that the spread of agriculture caused climate change.

In this case, the presumed culprit is forest clearance. Most of the land cultivated by early farmers in the Middle East, Europe and southern China would have been forested. When the trees that grew there were cleared, the carbon they contained ended up in the atmosphere as carbon dioxide, a greenhouse gas. Moreover, one form of farming—the cultivation of rice in waterlogged fields—generates methane, another greenhouse gas, in large quantities. William Ruddiman, of the University of Virginia, explained to delegates his theory that, in combination, these two phenomena had warmed the atmosphere prior to the start of the industrial era by as much as all the greenhouse gases emitted since.

Dr Ruddiman's hypothesis is grounded on recent deviations from the regular climatic pattern of the past 400,000 years. This pattern is controlled by what are known as the Milankovitch cycles, which are in turn caused by periodic changes in the Earth's orbit and angle of tilt toward the sun. One effect of the Milankovitch cycles is to cause regular and predictable changes in the atmospheric concentrations of carbon dioxide and methane. These changes can be followed by studying ice cores taken in Antarctica.