Thirty Years On, How Well Do Global
Warming Predictions Stand Up?
James Hansen issued dire
warnings in the summer of 1988. Today earth is only modestly warmer.
James E. Hansen wiped sweat from his brow. Outside it was a
record-high 98 degrees on June 23, 1988, as the NASA scientist testified before
the Senate Committee on Energy and Natural Resources during a prolonged heat
wave, which he decided to cast as a climate event of cosmic significance. He
expressed to the senators his “high degree of confidence” in “a
cause-and-effect relationship between the greenhouse effect and observed
warming.”
With that testimony and an accompanying paper in the Journal of Geophysical
Research, Mr. Hansen lit the bonfire of the greenhouse vanities, igniting a
world-wide debate that continues today about the energy structure of the entire
planet. President Obama’s environmental policies were predicated on similar
models of rapid, high-cost warming. But the 30th anniversary of Mr. Hansen’s
predictions affords an opportunity to see how well his forecasts have done—and
to reconsider environmental policy accordingly.
Mr. Hansen’s testimony described three possible scenarios for
the future of carbon dioxide emissions. He called Scenario A “business as
usual,” as it maintained the accelerating emissions growth typical of the 1970s
and ’80s. This scenario predicted the earth would warm 1 degree Celsius by
2018. Scenario B set emissions lower, rising at the same rate today as in 1988.
Mr. Hansen called this outcome the “most plausible,” and predicted it would
lead to about 0.7 degree of warming by this year. He added a final projection,
Scenario C, which he deemed highly unlikely: constant emissions beginning in
2000. In that forecast, temperatures would rise a few tenths of a degree before
flatlining after 2000.
Thirty years of data have been collected since Mr. Hansen
outlined his scenarios—enough to determine which was closest to reality. And
the winner is Scenario C. Global surface temperature has not increased
significantly since 2000, discounting the larger-than-usual El Niño of 2015-16.
Assessed by Mr. Hansen’s model, surface temperatures are behaving as if we had
capped 18 years ago the carbon-dioxide emissions responsible for the enhanced
greenhouse effect. But we didn’t. And it isn’t just Mr. Hansen who got it
wrong. Models devised by the United Nations Intergovernmental Panel on Climate
Change have, on average, predicted about twice as much warming as has been
observed since global satellite temperature monitoring began 40 years ago
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