In the early 21st century, it's become clear that air pollution can
significantly reduce the amount of sunlight reaching Earth, lower temperatures,
and mask the warming effects of greenhouse gases. Climate researcher James
Hansen estimates that "global dimming" is cooling our planet by more than a
degree Celsius (1.8°F) and fears that as we cut back on the pollution that contributes
to dimming, global
warming may escalate to a point of no return. Regrettably, in terms of possibly
taking corrective action, our current understanding of global dimming has been
a long time in the coming, considering the first hints of the phenomenon date back
to 18th-century observations of volcanic eruptions. In this slide show,
follow a series of historic events and scientific milestones that built the
case for global dimming. Click on the image at left to begin.—Susan K. Lewis
Thanks to Spencer Weart of the American Institute of Physics, whose book
The Discovery of Global Warming made this feature possible. A hypertext
version of the book can be found at www.aip.org/history/climate/
