In 1988, discussion of climate change was confined mainly to scientific journals and was unknown to most policymakers and the media. But on June 23, Senator Timothy Wirth convened a hearing of the Senate Energy Committee to explore the issue. The lead witness was Dr. James Hansen of NASA. His testimony marked the first time a top climate scientist declared that global temperatures had risen beyond the range of natural variability and that global warming was underway.

Dr. Hansen's testimony echoed around the world. He has turned out to be the Paul Revere of climate change. Mainstream scientific thinking has swung behind his 1988 testimony, and climate change now looms as a more immediate and serious threat than ever before. Because the world's governments have done little to slow emissions growth in the past two decades, immediate action is now needed.

On Monday, June 23, Dr. Hansen and Senator Wirth will share their views on how the science and policy of climate change have unfolded over the past two decades--and what must be done to avoid climate catastrophe in the decades ahead.