Celebrities, politicians, and media pundits often speak of the scientific consensus on the issue of global warming. But this presumed consensus is not what some might have us believe.

Most of the climate-science community is indeed united on one particular component of the issue: there is global climate change.  There has always been climate change, which is what makes this issue simple to agree on.  But there is far from unanimous agreement on whether modern climate change is more extreme than normal - or even on how best to define "normal" given the uncertainty in measuring long-past climate from secondary measures such as ice cores and tree rings.

There is even less agreement on the extent to which current and projected climate change is human-induced. Still, the scientific "consensus" is often presented as indisputable fact. 

In support of the consensus theory, many in the public spotlight point to a study by science history professor Naomi Oreskes, in which she reviewed the abstracts of 928 scientific papers published since 1993 with the keywords "global climate change" and found that none of them disagreed with the "consensus position" that the earth's climate is being affected by human activities.

Less frequently reported are the problems with Oreskes' study.  An independent review by British social scientist Benny Peiser repeated Oreskes' process but found that only 13 of 905 articles expressly supported the "consensus" view, and several actually opposed it. Further, 23 articles had no available abstract, meaning that the findings of those papers could not be concluded from this procedure. 

The Oreskes study, even ignoring its other flaws, attempted to condense the complex and diverse field of climate science into a binary measure.  In doing so, the study ignored the wide range of findings represented by all of these studies, and misrepresented the true breadth of viewpoints among climate science researchers.  Not challenging the idea that human activities may contribute to global warming is certainly not the same thing as endorsing the contention that human activities are the main contributor to contemporary climate change. Further, the significance of scientific consensus itself is often overstated. 

Science is not a democratic process: just because a majority thinks one thing doesn't mean it's so.  In fact, the most momentous advancements in science come from questioning generally accepted beliefs.  Scientific history offers us a nearly unlimited list of examples: that flies are spontaneously generated from meat, or that the earth is flat and the center of the universe.   In each case, the consensus of the experts was nearly unanimous, and wrong. The opposition changed the science. Even the quoted "consensus" exists with caveats that are frequently ignored. 

For example, in June the National Academy of Science issued a report on surface temperature reconstructions for the last 2000 years in which the panel stated that the so-called hockey stick model of increasing global temperatures was nothing more than "plausible," and in fact found "little confidence" could be given to reconstructions of millennia-old temperatures.  These cautions, however, were not reflected in the myriad headlines proclaiming that the Academy had endorsed the hockey stick model.

The media, celebrities, and politicians should recognize that there is far less consensus on the issue of climate change than many in the public eye would have us believe. The public has good reason to remain skeptical of those who say the case is closed.