While the public may understand little about climate science, nearly everyone has been exposed to the statement that there is a consensus among scientists regarding dangerous climate change. This chapter explores the history and consequences of the scientific consensus building activities undertaken by the Intergovernmental Panel on Climate Change (IPCC).

For genuinely well-established scientific theories, the concept of consensus is irrelevant. For example, there is no point in discussing a consensus that the Earth orbits the sun, or that the hydrogen molecule has less mass than the nitrogen molecule. While a consensus may arise surrounding a specific scientific hypothesis or theory, the existence of a consensus is not itself the evidence.

There is a key difference between a “scientific consensus” and a “consensus of scientists.” A scientific consensus is a relatively stable paradigm that structures and organizes scientific knowledge. By contrast, a consensus of scientists represents a deliberate expression of collective judgment by a scientific institution or a group of scientists, often at the official request of a government or other organization.

Under the auspices of the IPCC, the international climate community has worked for the past 30 years to establish a scientific consensus on human-caused climate change. The IPCC has codified consensus seeking into its assessment procedures: “In taking decisions, drawing conclusions, and adopting reports, the IPCC Plenary and Working Groups shall use all best endeavours to reach consensus.” The IPCC consensus has been described as a “manufactured consensus” (or a consensus of scientists), arising from an intentional consensus building process.

Among the best indicators to nonexperts about climate change is the existence of a consensus among experts. Messaging on the climate consensus went viral with this 2013 tweet from US President Obama:

President Obama's tweet linked to a paper by Cook et al. that analyzed the abstracts of almost 12,000 climate-related papers.