Senator Inhofe on Climate Change

by Michael Mann, Stefan Rahmstorf, Gavin Schmidt, Eric Steig, and William Connolley

Senator James Inhofe (R) of Oklahoma recently provided us with an update of his views on the issue of climate change in a speech given on the opening senate session, January 4, 2005. His speech opened with the statement:

As I said on the Senate floor on July 28, 2003, “much of the debate over global warming is predicated on fear, rather than science.” I called the threat of catastrophic global warming the “greatest hoax ever perpetrated on the American people,” a statement that, to put it mildly, was not viewed kindly by environmental extremists and their elitist organizations.

Cutting through much of his polemic, Inhofe’s speech contains three lines of scientific argument which, according to him, provide “compelling new scientific evidence” that anthropogenic global warming is not threatening. We here submit his statements to scrutiny.

(1) The Paleoclimate Record

Inhofe relies upon novelist Michael Crichton (see here and here) to support his contention that

“We are also in the midst of a natural warming trend that began about 1850, as we emerged from a 400 year cold spell known as the Little Ice Age.”

Scientific studies come to the opposite result. All published scientific investigations of the causes of 20th century warming have consistently found that natural factors alone cannot explain the warming. Model simulations of large-scale temperature changes in past centuries , for one, can only reproduce the post-“Little Ice Age” warming through the inclusion of non-natural, anthropogenic forcing. The IPCC concluded in its 2nd asessment report that “that there is a discernible human influence on global climate”, based in fact on a variety of different techniques, including so-called “Detection and Attribution” studies. These studies involve detailed analyses of the spatial patterns of the observed 20th century changes, which differ for different causes of warming (e.g. anthropogenic factors such as increased greenhouse gases or industrial aerosols, or changes in land use, and natural factors such as changes in solar output or explosive volcanism), each of which have their own unique spatial pattern or “fingerprint”. Another simple reason that natural causes cannot explain recent warming is that none of the natural factors which could potentially cause warming (e.g., the combined solar+volcanic forcing or even the somewhat more dubious hypothesized forcing by cosmic ray flux changes) show a trend since the mid 20th century.

Inhofe then launches into a slew of criticisms of the “Hockey Stick” reconstruction of past temperature changes in this speech, touching on every one of our documented “myths”. Consider, for example, his reference to

“the well-known phenomena of the Medieval Warming [sic] Period–when, by the way, it was warmer than it is today”

All quantitative paleoclimate reconstructions of the past millennium published in the scientific literature have come to the opposite conclusion. They consistently find that late 20th century warmth is anomalous in the context of at least the last 1000 years for the Northern Hemisphere on the whole. Though certain regions appear to have exhibited mild conditions during the so-called “Medieval Warm Period”, there is no credible evidence we are aware of that average temperatures for the Northern Hemisphere or globe were as warm as (let alone warmer than) the late 20th century.

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