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 NiƱo 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.
What about Mr. Hansen’s other claims? Outside the
warming models, his only explicit claim in the testimony was that the late ’80s
and ’90s would see “greater than average warming in the southeast U.S. and the
Midwest.” No such spike has been measured in these regions.
As observed temperatures diverged over the years from his
predictions, Mr. Hansen doubled down. In a 2007 case on auto emissions, he
stated in his deposition that most of Greenland’s ice would soon melt, raising
sea levels 23 feet over the course of 100 years. Subsequent research published
in Nature magazine on the history of Greenland’s ice cap demonstrated this to
be impossible. Much of Greenland’s surface melts every summer, meaning rapid
melting might reasonably be expected to occur in a dramatically warming world.
But not in the one we live in. The Nature study found only modest ice loss
after 6,000 years of much warmer temperatures than human activity could ever
sustain.
Several more of Mr. Hansen’s predictions can now be judged
by history. Have hurricanes gotten stronger, as Mr. Hansen predicted in a 2016
study? No. Satellite
data from 1970 onward shows no evidence of this in relation to
global surface temperature. Have storms caused increasing amounts of damage in
the U.S.? Data from the National Oceanic and Atmospheric Administration show no
such increase in damage, measured as a percentage of gross domestic product.
How about stronger tornadoes? The opposite may be true, as NOAA data offers
some evidence of a decline. The list of what didn’t happen is long and tedious.
The problem with Mr. Hansen’s models—and the U.N.’s—is that
they don’t consider more-precise measures of how aerosol emissions counter
warming caused by greenhouse gases. Several newer climate models account for
this trend and routinely project about half the warming predicted by U.N.
models, placing their numbers much closer to observed temperatures. The most
recent of these was published in April by Nic Lewis and Judith Curry in the
Journal of Climate, a reliably mainstream journal.
These corrected climate predictions raise a crucial
question: Why should people world-wide pay drastic costs to cut emissions when
the global temperature is acting as if those cuts have already been made?
On the 30th anniversary of Mr. Hansen’s galvanizing
testimony, it’s time to acknowledge that the rapid warming he predicted isn’t
happening. Climate researchers and policy makers should adopt the more modest
forecasts that are consistent with observed temperatures.
That would be a lukewarm policy, consistent with a
lukewarming planet.
Mr. Michaels is director
and Mr. Maue an adjunct scholar at the Cato Institute’s Center for the Study of
Science.
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