The Origins of Denial - The Hockey Stick and the Climate Wars - page 47

Lindzen—who also has received money from fossil fuel interests 40 —is perhaps best known for his
controversial views that climate models grossly overestimate the warming effect of increasing
greenhouse gas concentrations. It all has to do with the issue of climate feedbacks. Feedbacks, as we
have seen, are mechanisms within the climate system that can act either to amplify (positive feedback)
or diminish (negative feedback) the warming expected from increasing greenhouse gas
concentrations. If a climate scientist has spent a career looking for missing feedbacks in climate
models that are always of the same sign (positive for a “true believer” and negative for a “denier”),
one might reasonably suspect that the endeavor has not been entirely objective. (Ironically, the one
missing feedback I've argued for in the climate system is a negative one 41 —a rather inconvenient fact
for those who would like to label me a “climate change alarmist.”)
Lindzen has made a career of searching for missing feedbacks, but apparently only negative
ones. Indeed, it seems as if he has never met a negative feedback he didn't like. And he has been
quick to trumpet his claims of newly found negative feedbacks in op-eds, opinion pieces, and public
testimony, 42 arguing time and again that his findings point to an overestimation of warming by models
and are an indication that climate change is an overblown problem. Yet each of his past claims has
evaporated under further scrutiny.
For years, Lindzen has argued that hypothesized but as yet unestablished negative feedbacks in
the climate system will offset the very large positive feedbacks arising from increased evaporation of
water into the atmosphere and melting of snow and ice associated with global warming. He has
argued that a doubling of CO 2 concentrations will consequently only raise global average
temperatures by roughly 1°C (and with zero uncertainty!). Yet the diversity of evidence from the
paleoclimate and modern climate record suggests that less than 2°C warming for CO 2 doubling is
highly unlikely. 43
In 1990, Lindzen argued that a drying and cooling of the upper troposphere would mitigate
global warming, 44 but later in effect conceded that further work had demonstrated that the mechanism
he had proposed was not viable. 45 In 2001 he promoted a new hypothesis, the so-called “iris”
effect, 46 in which warming ocean temperatures would supposedly lead to fewer high clouds, causing
surface temperatures to cool down. 47 Once again, this hypothesis didn't hold up under scrutiny by
other scientists. 48
Undeterred, Lindzen claimed to find evidence for an additional, new negative cloud feedback,
this time based on a putative statistical relationship between tropical sea surface temperatures and
satellite measurements of the radiation escaping to space. 49 He claimed that when the tropics warm
up, there are more low reflective clouds, causing more solar radiation to be returned to space, thus
tending to cool the surface. When climate researcher Kevin Trenberth of the National Center for
Atmospheric Research (NCAR) and his collaborators examined Lindzen's claims closely, 50 however,
they found the data points Lindzen had chosen to be curiously selective, and the claimed relationship
not supported when a more objectively chosen sample was used. 51 A subsequent analysis by other
researchers concluded that the available data may actually support a positive overall cloud feedback,
not a negative one. 52
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