Top climate scientist James Hansen tells the story of his involvement in the science of and debate over global climate change. In doing so he outlines the overwhelming evidence that change is happening and why that makes him deeply worried about the future.

Why I Must Speak Out About Climate Change

By James Hansen, TED

08 March 12

Top climate scientist James Hansen tells the story of his involvement in the science of and debate over global climate change. In doing so he outlines the overwhelming evidence that change is happening and why that makes him deeply worried about the future.

James Hansen has made key insights into our global climate -- and inspired a generation of activists and scientists.

James Hansen is Adjunct Professor of Earth and Environmental Sciences at Columbia University’s Earth Institute. He was trained in physics and astronomy in the space science program of James Van Allen at the University of Iowa. His early research on the clouds of Venus helped identify their composition as sulfuric acid. Since the late 1970s, he has focused his research on Earth's climate, especially human-made climate change. Hansen is known for his testimony on climate change to congressional committees in the 1980s that helped raise broad awareness of the global warming issue. Hansen is recognized for speaking truth to power, for identifying ineffectual policies as greenwash, and for outlining the actions that the public must take to protect the future of young people and the other species on the planet.

"The scientific excitement in comparing theory with data, and developing some understanding of global changes that are occurring, is what makes all the other stuff worth it." - James Hansen