Global Warming Before Smokestacks

Did humans start changing the climate thousands of years ago?

Global Warming Before Smokestacks 1

Michael Yamashita, Aurora Photos

Millennia ago, did just a few farmers—similar to these in present-day Yunnan, China—change the course of global climate?

People have changed the planet's climate, warming the atmosphere by churning out greenhouse gases.

But that process didn't start during the Industrial Revolution. It began thousands of years ago, according to a controversial hypothesis, before anyone uttered the phrase "global warming."

The warming, triggered by a relative handful of farmers, some cutting and burning forests and others planting rice paddies, could be the best way to explain one of the strangest oddities in