Paul Crutzen

It was thanks to Paul Crutzen that we skirted a previous global atmospheric threat: the destruction of the stratospheric ozone layer. If the warnings from him and his fellow winners of the 1995 Nobel Prize in chemistry, Sherwood Rowland and Mario Molina, hadn't come when they did, the Antarctic ozone hole might have proved disastrous.

We would be wise to heed Crutzen on global warming, too, because he can fairly be described as the chief scientific caretaker of life on the planet. He suggested the potential climatic danger of nuclear war, a threat later popularized as "nuclear winter" by Carl Sagan. He has made major contributions to our understanding of acid rain and the effect of aircraft on the atmosphere. He has not flinched from speaking out even when it annoys industry or governments, and he does not hide his concern for the lack of U.S. leadership in addressing global warming. In contrast to the prompt attention paid to the ozone threat, foot-dragging on climate change has convinced Crutzen that major geo-engineering may be needed to cool the planet. He suggests a massive injection of sulfur into the stratosphere to form particles that reflect sunlight away. It's a radical proposal that just might jolt some politicians into realizing what researchers learned long ago: that this scientists' scientist always seems to be one step ahead of everybody else.

James Hansen, director of the NASA Goddard Institute for Space Studies, conducted climate research that raised the alarm on global warming