What The Science Says:
The 'OISM petition' was signed by only a few climatologists.

Climate Myth: Over 31,000 scientists signed the OISM Petition Project
The Petition Project features over 31,000 scientists signing the petition stating "there is no convincing scientific evidence that human release of carbon dioxide will, in the forseeable future, cause catastrophic heating of the Earth's atmosphere". (OISM)

There are several claims that large numbers of scientists do not agree with the theory of climate change, the best known of which is a petition organised by the Oregon Institute of Science and Medicine (the OISM petition). This petition now appears to be signed by over 32,000 people with a BSc or higher qualification. The signatories agree with these statements:

No evidence has ever been offered to support the first statement, and the second statement is in flat contradiction with the scientists who study climate change. There are also valid issues regarding the methodology:

In the professional field of climate science, the consensus is unequivocal: human activities are causing climate change and additional anthropogenic CO2 may cause great disruption to the climate.

32,000 Sounds Like A Lot

In fact, OISM signatories represent a tiny fraction (~0.3%) of all US science graduates (petition cards were only sent to individuals within the U.S)

According to figures from the US Department of Education Digest of Education Statistics: 2008, 10.6 million science graduates have gained qualifications consistent with the OISM polling criteria since the 1970-71 school year. 32,000 out of 10 million is not a very compelling figure, but a tiny minority - approximately 0.3 per cent.

There are many issues casting doubt on the validity of this petition. On investigation, attempts to undermine the scientific consensus on climate change often appear to have ideological roots, vested business interests or political sponsors. The claims made for the OISM petition do not withstand objective scrutiny, and the assertions made in the petition are not supported by evidence, data or scientific research.

Several studies conducted independently (Oreskes 2004, Oreskes 2007, Doran and Zimmerman (2009), Anderegg et al. (2010), Cook et. al., 2013) have shown that 97% of climate scientists agree that humans are causing the climate to change, and that anthropogenic greenhouse gases are causing global changes to the climate. These views form the scientific consensus on climate change.

Basic rebuttal written by GPWayne

Update July 2015:

Here is a related lecture-video from Denial101x - Making Sense of Climate Science Denial


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