One theory is that the dark native vegetation absorbs and releases more heat into the atmosphere than the light-colored crops. These native plants release heat that combines with water vapor from the lower atmosphere, resulting in cloud formation.

Image BOUNDARY A satellite image, above, and an aerial photograph of the rabbit-proof fence in Australia, separating dark native vegetation and light farmland. Credit... Above, NASA Goddard Space Flight Center; Top, Murdoch University

Another hypothesis is that the warmer air on the native scrubland rises, creating a vacuum in the lower atmosphere that is then filled by cooler air from cropland across the fence. As a result, clouds form on the scrubland side.

A third idea is that a high concentration of aerosols — particles suspended in the atmosphere — on the agricultural side results in small water droplets and a decrease in the probability of rainfall. On the native landscape, the concentration of aerosols is lower, translating into larger droplets and more rainfall.

Within the last few decades, about 32 million acres of native vegetation have been converted to croplands west of the bunny fence. On the agricultural side of the fence, rainfall has been reduced by 20 percent since the 1970s.

Dr. Nair speculates that increases in the world’s population will prompt the clearing of more land to increase food production. But he wonders whether, in the long run, “we will reach a point of land clearing that will diminish food production,” because rainfall has decreased.