Prehistoric farmers who slashed down trees and laid out the first rice paddies and wheatfields triggered major alterations to levels of greenhouse gases such as methane and carbon dioxide in the atmosphere, they say.
As a result, global temperatures - which were slowly falling around 8,000 years ago - began to rise. 'Current temperatures would be well on the way toward typical glacial temperatures, had it not been for the greenhouse gas contributions from early farming practices,' says Professor William Ruddiman of Virginia University.
The theory, based on studies of carbon dioxide and methane samples taken from Antarctic ice cores, is highly controversial - a point acknowledged by Ruddiman. 'Global warming sceptics could cite my work as evidence that human-generated greenhouse gases played a beneficial role for several thousand years by keeping the Earth's climate more hospitable than it would otherwise have been,' he states in the current issue of Scientific American.
'However, others might counter that, if so few humans with relatively primitive technologies were able to alter the course of climate so significantly, then we have reason to be concerned about the current rise of greenhouse gases to unparalleled concentrations at unprecedented rates.'
Elaborating on his theory, Ruddiman said: 'Rice paddies flooded by irrigation generate methane for the same reason that natural wetlands do - vegetation decomposes in the stagnant water. Methane is also released as farmers burn grasslands,' Ruddiman points out.
Similarly, the cutting down of forests had a major effect. 'Whether the fallen trees were burnt or left to rot, their carbon would soon have been oxidised and ended up in the atmosphere as carbon dioxide.'
Climate Change Killed Neandertals, Study Says
Both Neandertals and the first humans to reach Europe struggled with the changing conditions brought by increasingly cold temperatures, according to a study by 30 scientists.
The two species coexisted in Europe from roughly 45,000 to 28,000 years ago when the Neandertals died out. Why humans survived and the Neandertals didn't has puzzled archaeologists for over a century.
Theories have ranged from interspecies genocide to interbreeding to humans' superior communication skills, hunting technology, and social organization.
The new study—a seven-year effort that combined the work of 30 scientists from 11 nations—suggests, however, that the inability to adapt to climate change led to the Neandertals' demise.
"It's not that it got too cold for them; both humans and Neandertals had clothing such as fur mantles," said Jerry van Andel, a geologist at the University of Cambridge in the United Kingdom who led the study.
Rather, researchers believe Neandertals failed to adapt their hunting methods when big game species like mammoth (Mammuthus primigenius), bison (Bison bonasus), and red deer (Cervus elaphus) fled south and the once-forested landscape of Europe changed into a sparsely vegetated steppe and half desert during the last Ice Age.
Which just goes to show there are swings and roundabouts in every climatic change. I promise the Ruddiman study will get misreported as evidence that global warming does not mean we should do anything to mitigate its effects. I also promise the right lobe of the blogosphere will not draw the obvious linkage between their own refusal to adapt and the sad fate of our Neanderthal cousins.