More than 20 years ago, climate scientists began to raise alarms over the possibility global temperatures were rising due to human activities, such as deforestation and the burning of fossil fuels.

To better understand this potential threat, the World Meteorological Organization and the United Nations created the Intergovernmental Panel on Climate Change (IPCC) in 1988 to provide a "comprehensive, objective, scientific, technical and socioeconomic assessment of human-caused climate change, its potential impacts and options for adaptation and mitigation."

IPCC reports have predicted average world temperatures will increase dramatically, leading to the spread of tropical diseases, severe drought, the rapid melting of the world's glaciers and ice caps, and rising sea levels. However, several assessments of the IPCC's work have shown the techniques and methods used to derive its climate predictions are fundamentally flawed.

In a 2001 report, the IPCC published an image commonly referred to as the "hockey stick." This graph showed relatively stable temperatures from A.D. 1000 to 1900, with temperatures rising steeply from 1900 to 2000. The IPCC and public figures, such as former Vice President Al Gore, have used the hockey stick to support the conclusion that human energy use over the last 100 years has caused unprecedented rise global warming.

However, several studies cast doubt on the accuracy of the hockey stick, and in 2006 Congress requested an independent analysis of it. A panel of statisticians chaired by Edward J. Wegman, of George Mason University, found significant problems with the methods of statistical analysis used by the researchers and with the IPCC's peer review process. For example, the researchers who created the hockey stick used the wrong time scale to establish the mean temperature to compare with recorded temperatures of the last century. Because the mean temperature was low, the recent temperature rise seemed unusual and dramatic. This error was not discovered in part because statisticians were never consulted.

Furthermore, the community of specialists in ancient climates from which the peer reviewers were drawn was small and many of them had ties to the original authors — 43 paleoclimatologists had previously coauthored papers with the lead researcher who constructed the hockey stick.

These problems led Mr. Wegman's team to conclude that the idea that the planet is experiencing unprecedented global warming "cannot be supported."

The IPCC published its Fourth Assessment Report in 2007 predicting global warming will lead to widespread catastrophe if not mitigated, yet failed to provide the most basic requirement for effective climate policy: accurate temperature statistics. A number of weaknesses in the measurements include the fact temperatures aren't recorded from large areas of the Earth's surface and many weather stations once in undeveloped areas are now surrounded by buildings, parking lots and other heat-trapping structures resulting in an urban-heat-island effect.

Even using accurate temperature data, sound forecasting methods are required to predict climate change. Over time, forecasting researchers have compiled 140 principles that can be applied to a broad range of disciplines, including science, sociology, economics and politics.

In a recent NCPA study, Kesten Green and J. Scott Armstrong used these principles to audit the climate forecasts in the Fourth Assessment Report. Messrs. Green and Armstrong found the IPCC clearly violated 60 of the 127 principles relevant in assessing the IPCC predictions. Indeed, it could only be clearly established that the IPCC followed 17 of the more than 127 forecasting principles critical to making sound predictions.

A good example of a principle clearly violated is "Make sure forecasts are independent of politics." Politics shapes the IPCC from beginning to end. Legislators, policymakers and/or diplomatic appointees select (or approve) the scientists — at least the lead scientists — who make up the IPCC. In addition, the summary and the final draft of the IPCC's Fourth Assessment Report was written in collaboration with political appointees and subject to their approval.

Sadly, Mr. Green and Mr. Armstrong found no evidence the IPCC was even aware of the vast literature on scientific forecasting methods, much less applied the principles.

The IPCC and its defenders often argue that critics who are not climate scientists are unqualified to judge the validity of their work. However, climate predictions rely on methods, data and evidence from other fields of expertise, including statistical analysis and forecasting. Thus, the work of the IPCC is open to analysis and criticism from other disciplines.

The IPCC's policy recommendations are based on flawed statistical analyses and procedures that violate general forecasting principles. Policymakers should take this into account before enacting laws to counter global warming — which economists point out would have severe economic consequences.