A mainstay of environmentalists’ arguments for climate policies is that science can explain the past and present temperature of the planet, and, using computer models, project its likely future temperature. But, since the late 1990s, observations of temperature have deviated from models. The Earth is not as warm as it was expected to be. For many years, this deviation was denied, but it has recently been accepted by mainstream science. This is progress. But it has proven to be inconvenient to the political agendas attached to the climate-change narrative. In response, many theories have been proposed to explain where the ‘missing heat’ may be hiding out.