NCPA | Study #308, Global Warming: Experts’ Opinions versus Scientific Forecasts

More than 20 years ago, scientists began to express concern that human activities — primarily tropical deforestation and the burning of fossil fuels for energy — threaten to cause a rapid warming of the Earth by adding carbon dioxide (CO2) to the atmosphere. Recognizing the problems that global warming might cause, in 1998 the World Meteorological Organization (WMO) and the United Nations Environment Program (UNEP) established the Intergovernmental Panel on Climate Change (IPCC).² The purpose of the IPCC was to provide a comprehensive, objective, scientific, technical and socio-economic assessment of the current understanding of human-induced climate change, its potential impacts and options for adaptation and mitigation.

In 2007, the IPCC issued its Fourth Assessment Report. The Assessment in fact consists of three reports and a “synthesis” report. The first part was titled “The Physical Science Basis” and was authored by the IPCC’s Working Group One (WG1), a panel of experts on climate science, modeling and history. This paper focuses on the first report.³ It included predictions of dramatic increases in average world temperatures by 2100, which might in turn cause such serious environmental harms as: a global sea level rise that would threaten low-lying coastal areas, the spread of tropical diseases, an increasingly rapid loss of the world’s glaciers and ice caps, and a worsening of drought and flooding events across broad regions.⁴

Although the IPCC’s 1,056-page report makes these dire predictions, nowhere does it refer to empirically-validated forecasting methods, despite the fact these are conveniently available in books and articles and on Web sites. These evidence-based forecasting principles have been validated through experiment and testing and comparison to actual outcomes. The evidence shows that adherence to the principles increases forecast accuracy. This paper uses these scientific forecasting principles to ask: Are the IPCC’s forecasts a good basis for developing public policy? The answer is “no.”

Three elements are necessary for governments to make rational policy responses to climate change: Scientists must accurately predict (1) global temperature, (2) the effects of any temperature changes and (3) the effects of feasible alternative policy responses. At any step in this process, the failure to obtain a valid forecast would render forecasts at the next step in the process meaningless. This study focuses primarily, but not exclusively, on the first of the three forecasts required: obtaining long-term forecasts of global temperature. It finds that due to the unscientific method by which these forecasts were obtained, they cannot be relied upon. [See the sidebar, “Three Forecasts Required for Climate Change Policies.”]

Three Forecasts Required for Climate Change Policies

Before they can determine the best policies to deal with the climate of the future, policymakers must select an appropriate statistic to use to represent the changing climate. By convention, the statistic is the averaged global temperature as measured with thermometers at ground stations throughout the world. However, in practice this is a far from satisfactory metric. For instance:

Stations for taking temperature readings are absent from large areas of the Earth’s surface.
Temperature measurements are biased due to the urban-heat-island effect, whereby weather stations located originally on the edge of town became surrounded by buildings, factories, roads, cars, car parks and airport tarmacs; temperature measures from such stations don’t accurately represent the temperature for the larger surrounding area.
The locations and number of measuring stations have changed, which calls into question the consistency of measurements over time and the comparability of past measurements to present
ones.¹

However, assuming the problems with obtaining accurate current temperature measurements is resolved, the first step is to obtain forecasts and prediction intervals for the long-term mean global temperature (say 20 years or longer).

If accurate forecasts of mean global temperature can be obtained and the changes are substantial,
the second step is to obtain forecasts of the effects of temperature changes on humans and other living things. Concerns about changes in global mean temperature assume the earth is currently at the optimal temperature and that variations over years (unlike variations within days and years) are undesirable,
but a proper assessment requires comprehensive projections of both the costs and the benefits of changes from the current global average temperature.²

If valid forecasts of the effects of the temperature changes on the health of living things and on the health and wealth of humans can be obtained and substantial harmful effects are forecast, the third step is to calculate the costs and the benefits of proposed alternative policy responses. A policy proposal
should only be implemented if valid and reliable forecasts of the effects of implementing the policy can be obtained and the forecasts show net benefits.

¹C. Essex, R. McKitrick and B. Andresen, “Does a global temperature exist?” Journal of Non-Equilibrium Thermodynamics,
Vol. 32, No. 1, February 2007, pages 1-27. Working paper available at http://www.uoguelph.ca/~rmckitri/research/
globaltemp/globaltemp.html. Access verified December 10, 2007.

² For example, policy responses to Rachel Carson’s Silent Spring should have been based in part on forecasts of the number of people who might die from malaria if DDT use were reduced. Instead, the use of DDT was banned solely on the basis of predicted harm to bird species. Consideration of the one million human deaths and between 300 and 500 million cases of malaria annually might have led to a policy other than outright proscription. United Nations International
Children’s Emergency Fund (UNICEF), “Malaria,” undated. Available at http://www.unicef.org/health/index_malaria.html. Access verified December 10, 2007.