Christopher Doughty, a post-doctoral researcher at the Carnegie Institution for Science in Stanford, California, has led a team of researchers that has reached some controversial and unusual claims about mankind's role in changing the Earth's climate.

Doughty, in a paper published [PDF] in the journal Geophysical Research Letters, claims that the extinction of woolly mammoths may have triggered a cascade of effects warming Siberia and neighboring Beringia by at least 0.3 to 0.4 degrees Fahrenheit.  If these controversial claims prove true, it would likely be the first example of man influencing the world's climate in humanity's brief history as a species.

The report may change preconceptions about climate change, claims Doughty; "Some people say that people are unable to affect the climate, that it's just too big.  That's obviously not the case. People started to affect global climate much earlier than we thought."

Previous studies had indicated that mankind's development of agriculture 8,000 years ago could have changed the Earth's climate, but the effects of hunting in mankind's earlier days were not thought to have had significant impact.  The new study draws its basis from a previous study in the November 20, 2009 edition of the journal Science.  That study indicated that mammoths kept small trees in check, preserving grasslands.  With their extinction, the darker trees grew, increasing the overall darkness of the terrain, absorbing more solar radiation, and ultimately triggering a warming effect.

The issue with that study was that it posed a chicken-and-the-egg sort of conundrum; warming climates would encourage tree growth over tundra grasslands, but tree growth could also trigger warming.  Doughty claims in his new study that in the 850-year period where most of the mammoths disappeared from hunting, the levels of birch pollen increased by 26 percent.  Using modern elephant data, it was estimated that 23 percent of this increase came from the death of the mammoths, while the rest was caused by the heating trend itself.

The team then compiled vegetation loss findings and climate simulations to pinpoint how much of an impact the forestation increased had.  They found that it likely raised temperatures from 0.4 degrees F to the nearly 1 degree F.

Doughty admits in the study that it's not been conclusively shown that humans caused the extinction of mammoths in the first place (again, this is a chicken-egg riddle as warming climates could have pushed them to extinction, but their extinction could have warmed climates).  Man did hunt the beasts, and its the prevailing theory that we played at least a small role in their extinction.

The study was funded by NASA and the Carnegie Institution for Science.