Ruth DeFries

The loss of tropical forests worldwide is a big part of the climate change puzzle, and we wouldn't know it if it weren't for Ruth DeFries. Her innovative use of satellite images-or "remote sensing"-to study how humans are changing their planet has revealed some of science's big surprises, from the rate and extent of rainforest loss in the Amazon to the role urban areas play in deforestation. It has also revolutionized how governments respond to land use change, because many now employ her techniques to monitor and protect their natural resources. DeFries, the recipient of a 2007 MacArthur Foundation "genius" grant, is currently the Denning Professor of Sustainable Development at Columbia University in New York City. She was elected to the National Academy of Sciences in 2006.