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/
