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climate change could be natural was said to be provided by a medieval warm period as warm as, or
warmer than, today. Such a period of comparable warmth in the not-so-distant past, the logic goes,
would imply that modern warming could be natural, too. The logic is flawed, however: The mere
existence of a past warm period says nothing about the cause of the current warming. Even a modestly
(say, 1 percent) brighter Sun during preindustrial times, for example, could have led to conditions
warmer than today. Reconstructions of past temperatures such as the hockey stick (and the many other
reconstructions coming to similar conclusions) indicated that peak medieval warmth did not rise to
modern levels of warming in any case. That finding may have taken away a convenient contrarian
talking point. But the finding was hardly necessary to render implausible the argument that natural
variability could account for modern warming. To reach that conclusion it was sufficient to show, as
many studies now did, that models could not reproduce the anomalous warming of the past century
from natural factors alone. Only human impacts could explain that warming.
Judgment: pillar
toppled.
Heads of the Hydra
The complete or near collapse by 2007 of the pillars of defensible climate change skepticism
represented a critical juncture in the debate over the science. Would climate change contrarians throw
in the towel and at least concede the reality of human-caused climate change? Would they engage
constructively in the discourse, focusing their efforts on the legitimate remaining uncertainties, such as
the uncertain nature of climate change projections and the worthy debate to be had regarding what to
do about the problem? Or would they retrench and continue to contest the ever-accumulating evidence
supporting the reality of the climate change problem? The question is of course rhetorical; we already
know the answer.
In Greek mythology, one of the tasks of Hercules was to destroy the nine-headed creature known
as the Hydra. He found to his dismay that every time he cut off one of the heads, two would grow
back in its place. So it was now with climate change denial. For every talking point that was refuted,
two more would be offered. Moreover, the same arguments were eventually recycled, no matter how
many times they were refuted in the peer reviewed literature. Whether or not a talking point is
scientifically or even logically defensible is immaterial. If it has misinformed or confused an
appreciable number of observers, it has served its purpose in manufacturing doubt and confusion.
Far-right media outlets, Internet disinformation sites, and contrarian blogs are still peddling
factoids that were discredited in the actual scientific literature years ago, but that nonetheless endure
in the contrarian mythology. Any bit of new information that might be twisted to reinforce the denialist
canon is jumped on, while contradictory evidence is ignored or denounced. In the year or two
following the release of the AR4 report, for example, the contrarian canard
du jour
was that the globe
was in reality cooling—or at least not warming. The claim derived its credibility from contrarian
folklore such as “climate scientists were predicting global cooling in the 1970s” and the now
discredited “no warming” claim of Christy and Spencer.
The “globe is cooling” myth (and its sister, “global warming has stopped”) soon gained new life
through distortions of a 2008 article in
Nature
. Scientists from the Max Planck Institute for
Meteorology had used climate model simulations to demonstrate that long-term greenhouse warming
