The hypothesis of global warming includes the presumption that late 20th century warming was caused by human emissions. This theory has failed the three main tests to which it has been subjected. First, there is no relationship between the 20th century patterns of increasing carbon dioxide and changing temperature; second, 20th century rates and magnitude of temperature change fall well within previous natural limits of change despite accompanying increases in human-sourced carbon dioxide; and, third, the computer models used to engender public alarm have proved unable to predict temperature change over the period 1990 -2006, let alone out to 2100.