Besides killing many people, the eruption of Mount Pinatubo
destroyed homes and farmland, and caused hundreds of millions
of dollars in damage. At the same time, it enabled scientists to
test whether they understood the global climate well enough
to estimate how the eruption would affect temperatures on the
earth.
By the late 1980s, most of the world’s climate scientists had
become concerned that human actions, especially fossil fuel
use, were enhancing the world’s natural greenhouse effect and
contributing to a rise in the average temperature of
the atmosphere, which in turn would begin changing
the earth’s climate. Some stated publicly that climate
change from such global warming was very likely to occur
and could have disastrous ecological and economic
effects. Their concerns were based in part on results
from computer models of the global climate. But were
these models reliable?
Although their complex global climate models
mimicked past and present climates well, Mount
Pinatubo provided them with an opportunity to perform
a more rigorous test of such models. Soon after
the volcano erupted, James Hansen, a leading U.S.
National Aeronautics and Space Administration (NASA)
scientist, estimated that the Pinatubo explosion would
probably cool the average temperature of the earth by
0.5 C° (1 F°) over a 19-month period. The earth would
then begin to warm, Hansen said, and by 1995 would
return to the temperatures observed before the explosion.
His projections turned out to be correct.
To make his forecasts, Hansen added the estimated
amount of sulfur dioxide released by the volcano’s
eruption to a global climate model and then used
the model to forecast how the earth’s temperature
would change. His model passed the test with flying
colors. Its success helped to convince most scientists
and policy makers that climate model projections—
including those relating to the impact of human
actions—should be taken seriously.
Hansen’s model and 18 other climate models indicate
that global temperatures are likely to rise several
degrees during this century—mostly because of human
actions—and to affect global and regional climates and
economies and human ways of life. To many scientists
and a growing number of business executives, global
climate change represents the biggest challenge that
humanity faces during this century. The primary question
is, “What should we do about it?”