For many Americans, 2013 ended with an unusually bitter cold spell.

Marine life may be affected too: El ni?os can reduce the rising of the cold, nutrient-rich water that supports large fish 35 populations, and the unusually warm ocean temperatures can destroy coral.

The result is a sort of high-quality, unusually rigorous coffee-table book, designed to be dipped into rather than read from beginning to end.

The picture worsens with each round of El Nino, the unusually warm currents in the Pacific Ocean that drive up temperatures and invariably presage (預示) droughts and fires in the rain forest

That's an unusually large drop," Plant says.

While Maple Hill's conversion program is unusually hands on and comprehensive, it's just one of a growing number of businesses committed to slowly changing the way America farms.