Global Warming: Experts’ Opinions versus Scientific Forecasts

Policy Reports | Global Warming

No. 308
Friday, February 01, 2008
by Kesten C. Green and J. Scott Armstrong


Three elements are necessary for governments to make rational policies in response to climate change:  Scientists must accurately predict (1) global temperature changes, (2) the effects of any temperature changes and (3) the effects of feasible alternative policy responses.  To justify policy changes, governments need scientific forecasts for all three forecasting problems and they need those forecasts to show net benefits flowing from proposed policies.  If governments implement policy changes without such justification, they are likely to cause harm.

This paper has shown that failure occurs with the first forecasting problem:  predicting temperature over the long term.  Specifically, no scientific forecast supports the widespread belief in dangerous human-caused “global warming.”  Climate is complex and there is much uncertainty about causal relationships and data.  Prior research on forecasting suggests that in such situations a naïve (no change) forecast would be superior to current predictions.  Note that recommending the naïve forecast does not mean that climate will not change.  It means that current knowledge about climate is insufficient to make useful long-term forecasts about climate.  Policy proposals should be assessed on that basis.

Many policies have been proposed in association with claims of global warming.  This paper does not purport to comment on specific policy proposals, but it should be noted that some policies may be valid regardless of future climate changes.  To assess this, it would be necessary to directly forecast costs and benefits that assume: (1) that climate does not change and (2) that climate changes in a variety of ways.

The evidence shows that those forecasting long-term climate change have limited or no apparent knowledge of evidence-based forecasting methods; therefore, similar conclusions apply to the second two elements of the forecasting problem. Public policy makers owe it to the people who would be affected by their policies to base them on scientific forecasts.  Advocates of policy changes have a similar obligation.  Hopefully, climate scientists with diverse views will begin to embrace forecasting principles and will collaborate with forecasting experts in order to provide policy makers with scientific climate forecasts.

NOTE: Nothing written here should be construed as necessarily reflecting the views of the National Center for Policy Analysis or as an attempt to aid or hinder the passage of any bill before Congress.

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