Less than four centuries ago, life was colder in the northern latitudes than it is today. Alpine glaciers advanced, frost killed ancient orange groves in China, and Londoners held winter festivals on the frozen Thames. The Little Ice Age began around 1300 and lasted some 600 years. But according to a new theory, similar or even worse conditions might prevail today had it not been for the activities of prehistoric people. Most scientists agree that humans have had a hand in warming Earth's climate since the industrial revolution ― some even argue that we are living in a new geological epoch, dubbed the Anthropocene. But a respected climate scientist is now claiming that our involvement in climate change began thousands of years earlier and has led to more than twice as much warming as previously estimated ―enough to stave off a mini ice age. According to Bill Ruddiman, an emeritus professor at the University of Virginia, Char-lottesville, humans first began to affect the climate when clear-cutting of forests for agriculture spread from the eastern Mediterranean to Eurasia 8,000 years ago. The process boosted atmospheric levels of carbon dioxide ― the main greenhouse gas ― by releasing carbon stored in the trees. Then, about 5,000 years ago, southeast Asians inadvertently began adding the greenhouse gas methane to the atmosphere when they flooded fields to grow rice, effectively creating artificial wetlands.
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