James Hansen is best known for his expertise on climatology and global warming. A professor at Columbia University and former director of the NASA Goddard Institute for Space Studies, Hansen is considered the ‘father of global warming,' due to his warnings in the 1980’s. His early research confirmed that the clouds on Venus are composed of sulfuric acid. He has since shifted his focus to human impact on the Earth's climate. Hansen was elected to the National Academy of Sciences in 1995, and was listed as one of Time magazine's ‘Most Influential People’ in 2006.