The Cornell team said the risks to monarchs could be heightened because the butterflies migrate northward through the U.S. Corn Belt from their winter homes in Mexico during the spring months, when corn pollen is thickest.

CNN: Researchers find bio-engineered corn harms butterflies

About 250km (150 miles) to the north, in neighbouring Shanxi province, in Pingdong, a much poorer village, 250 people live along battered dirt roads, and try to grow wheat, corn, soyabeans and winter melon on the dry, rocky mountain land.

ECONOMIST: Farmers pay the price for decades of wasteful water use

The explained variance of this residual yield by climate is generally about 50%, which is very close to the average I found for corn, soybeans, and winter wheat.

FORBES: Climategate II: An Open Letter to the Director of the National Center for Atmospheric Research