Would you be willing to brave the risks of extreme altitude – temporary blindness, ruptured lungs, and blood clots – to obtain prehistoric ice samples and piece together tens of thousands of years of weather history? Lonnie Thompson is, and it has made him one of the most influential scientists in the effort to crack the code of climate change.

Director of Ohio State University’s Polar Research Center, “Thompson has spent more time above 18,000 feet than any other person on Earth,” according to a Rolling Stone profile. He goes to the far-reaches of the planet – be it the glaciers of the Himalayas, Kilimanjaro, or the peaks of the Andes – and extracts ice core samples. He stores them in giant refrigerated vaults in Ohio, and deciphers the atmospheric particles captured within tiny bubbles in the ice.

From these molecules he can determine both the annual temperatures and levels of greenhouse gasses in the atmosphere dating back over a hundred thousand years. The upshot of his research so far? Average global temperatures are warmer today than they have been for over 6000 years.

Photo credit: CNN.com, Photograph for TIME by Mark Katzman – FK Photo