Int. J. Environ. Res. Public Health 2011, 8 2. The Economic Benefits of Climate Change Mitigation 2.1. The Background 992 Beginning in the 1980s, the United Nations attempted to determine the extent to which global warming may be due to human activities in a series of reports prepared by its IPCC. The most recent of these was issued in 2007 and is usually referred to as the AR4 report [5]. It is important to note that the IPCC‘s charge is not to determine what causes global warming but rather whether it results from human activities. They have orchestrated worldwide concern about global warming with strong support from many Western governments, some academics, and most environmental organizations. They concluded that this warming could be mitigated by reducing human emissions of greenhouse gases, particularly carbon dioxide (CO2). One of the immediate questions was what the economic benefits of such reductions might be. There have been numerous attempts to determine this by economists, ranging from the technically sophisticated to the more easily understood by the public (see Section 5 below for a list of many of these). In all major cases I know of those preparing the benefit estimates assumed that the IPCC conclusions concerning the effects of decreasing carbon dioxide and other greenhouse gas emissions were substantially correct and accurate. It is not clear why they all assumed this, however, since as will be shown for particular instances later in this section, key conclusions reached by the IPCC are not supported by the most relevant observational tests and the scientific method (see Section 1.2 above for a discussion of the scientific method and its role in determining what is valid science), and therefore have no standing as science despite numerous statements to the contrary by CAGW supporters. Idso and Singer [6] have compiled an extensive listing of many of these problems. The IPCC‘s timing was excellent since in fact Earth appears to have been in a minor periodic warming period according to ground-based measurements. This minor warming started in the late 1970s and may have peaked in 1998, and followed a much longer standing even more gradual warming that has taken place since the end of the Little Ice Age. A gross generalization is that the IPCC models effectively hypothesized that this minor periodic warming would continue during the 21st century even though similar periodic warming and cooling has been going on since at least the late 19th century and probably for much longer. Although it is not clear whether humans as a whole would on balance be better or worse off as a result of the presumed rise in global temperatures hypothesized by the IPCC, the CAGW promoters managed to sell a major scare to a surprising number of people and government officials through a variety of means. Their views have even been endorsed by most of the national academies of science around the world. Major Western European nations and the European Union enacted significant legislation that would reduce the global warming, or so it was claimed. The United States House of Representatives passed related legislation [7] in 2009, but it was not passed by the Senate and died at the end of the 111th Congress in 2010. The various UN IPCC reports broadly argue that the authors cannot think of any reasonable source of global warming other than the increasing level of some GHGs, so that must be the cause. There are a few exceptions, such as large volcanic eruptions, which they agree may influence global temperatures, but they do not believe that the warming can be attributed to most other natural causes