Richard Tol: Moderate Global Warming Is Good For The World

In recent years, more estimates of the economic impact of climate change have been published. They show positive impacts for warming up to about two degrees Celsius of global warming.

In a recent article on these pages, Mr Robert ET Ward BSc misrepresents the economic literature on the impacts of climate change and impugns my character. I am grateful to the editors of the Huffington Post for allowing me to set the record straight.

Mr Ward claims that there are “significant errors in [a] study suggesting global warming is good for the world”. That study is a survey published by me in 2009. There were errors in that survey, now corrected, but the headline conclusions did not change. The latest survey contains four studies – by the late Ralph d’Arge, Robert Mendelsohn of Yale University, David Maddison of Birmingham University and myself – that conclude that climate change would improve human welfare. None of these studies have been found to be in error.

Climate change has many impacts, some small, some large, some positive, some negative. The main positive effects are that warmer winters would reduce spending on heating houses, and reduce cold-related deaths. More carbon dioxide in the atmosphere would be a boon to crops, particularly in semi-arid areas. For moderate climate change, these positive impacts appear to outweigh the negative ones. For more profound warming, the negative impacts dominate.

Mr Ward claims that I “refused to give an undertaking to correct his journal papers”. In fact, I only refused to regularly brief Mr Ward, who had uncovered a single typo. Indeed, all known errors have been corrected, and a number of errata have been published.

There is one issue outstanding. One editor of a learned journal argued that a comment plus rejoinder would be more informative than a corrigendum. Mr Ward was invited to submit his comment in March 2014, but has yet to do so.

Mr Ward claims that “mistakes had been corrected” in the Fifth Assessment Report of Working Group II of the Intergovernmental Panel on Climate Change. In fact, we replaced the vague “may be beneficial” with the precise “17 out of 20 are negative”, in line with the IPCC style which frowns on ambiguous wording and emphasizes the more likely outcomes. Still, the IPCC reports both beneficial and harmful impacts -as did the final draft.

Mr Ward highlights “shortcomings in the trend that [I] had fitted to the data”. In fact, the original and corrected data are not materially different. There is no statistically significant difference between the trends fitted to the original data and to the corrected data.

Since 2009, however, more estimates of the economic impact of climate change have been published. These new results do affect the fitted trend, but not in the way suggested by Mr Ward. The new trend shows positive impacts for warming up to about two degrees global warming, just like the old trend did. The new trend, however, shows markedly less negative impacts for more profound warming than did the old trend. In other words, in the last five years, we have become less pessimistic about the impacts of climate change.

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