James Hansen talks about climate change.

• Position: INTERVIEW - Interview

Editor's Note: If any single event can be said to have put climate change on the world's policy radar, it was the testimony of NASA scientist James Hansen before Senator Tim Wirth's committee in Congress on June 23, 1988. On the eve of the twentieth anniversary of that event, World Watch's Ben Block talked with Hansen about its impact. Hansen will be honored at a Worldwatch Institute-sponsored symposium in Washington, D.C., on June 23, 2008. For more information, go to www.worldwatch.org/events/hansenhearing.

World Watch: What led you to your 1988 testimony?

James Hansen: This was the culmination of years of work, going back at least to three papers between 1981 and 1982, [discussing] carbon dioxide and climate change in the journal Science, other trace gases in Geophysical Research Letters, and sea level, also published in Science. What was different in 1988 was that I had a more comprehensive paper completed and in press at Journal of Geographical Research, which was the attachment to my 1988 testimony.

WW: What did you expect the impact of your testimony would be?

JH: Well, the intention was to get some public exposure. Rafe Pomerance [founder of the Climate Policy Center, who was then a World Resources Institute senior fellow] visited me after reading our 1981 Science paper [on carbon dioxide] and encouraged me to testify to Congress, which I did a few times in the 1980s without much effect. The hope was to get more attention this time, which seemed possible given the extreme U.S. climate [hot weather] in 1988.

WW: Looking back, how did it go?

JH: It certainly got the desired attention. My regret, shortly thereafter, was that I had not discussed the impact of global warming on the hydrologic cycle in a more general way. Global warming means more moisture in the atmosphere, so heavy rain events and floods will increase. But, at times and places when it is dry, drought intensity will increase. Because of the emphasis on drought in 1988, I decided to testify again in 1989. That testimony got a lot of attention also, because I complained about [the White House's Office of Management and Budget] changing my testimony, but that hullabaloo caused the message about the hydrologic cycle to be lost.

WW: When many scientists responded to the '88 testimony that you were "ahead of the science," how did you react?

JH: I was not too concerned about that, I knew that within not many years it would become obvious whether or not I was right. Since I was...