Significant Errors in Study Suggesting Global Warming is Good for the World

09/02/2015 13:02 | Updated 08 April 2015
  • Bob Ward Policy and Communications Director, Grantham Research Institute on Climate Change and the Environment

The new issue of the Journal of Economic Perspectives includes a remarkable admission about a controversial academic paper that wrongly suggested moderate amounts of global warming would have an overall positive economic impact on the world.

The paper by Richard Tol, who is now a professor of economics at the University of Sussex, has been widely promoted by climate change 'sceptics' who have attempted to argue that global warming is not a problem.

But editors at the journal have now finally acknowledged that the original paper contained a number of significant errors that render invalid its conclusion about beneficial global warming.

In 2009, the journal published 'The Economic Effects of Climate Change' by Professor Tol, which used estimates of the impacts of climate change from a number of previous studies to show how they would change as global average surface temperature increases.

Among its conclusions were that global warming of upto two centigrade degrees or so could have a net positive economic impact.

Professor Tol added to and updated his analysis in subsequent papers for other journals, but reached the same general conclusion.

Unfortunately, his papers contained a number of errors because he had inadvertently misrepresented the results of some of the studies of economic impacts.

In particular, Professor Tol's 2009 paper suggested that a study in 1996 by Erica Plambeck and Chris Hope of the University of Cambridge had estimated a net positive impact equivalent to 0.9 per cent of GDP due to global warming of 2.5 centigrade degrees, when in fact the authors had found a negative effect.

I first became aware of the errors in Professor Tol's work when his 2009 paper was cited by Viscount Ridley in an article for The Spectator magazine in October 2013, which proclaimed on its front page 'Why climate change is good for the world'.

Professor Tol and Viscount Ridley are both members of the all-male "Academic Advisory Council" of the Global Warming Policy Foundation, which was launched by Lord Lawson in November 2009 to campaign against Government climate change policies.

I contacted Professor Tol in October 2013 to alert him to the errors in his work. While he acknowledged some of the mistakes, he refused to give an undertaking to correct his journal papers.

In January 2014, I discovered that a section based on one of Professor Tol's faulty papers had been inserted into the final draft of a chapter of a report on 'Impacts, Adaptation and Vulnerability' by the Intergovernmental Panel on Climate Change (IPCC).

It reproduced some of the errors that occurred in Professor Tol's paper, including the inaccurate claim that "Climate change may be beneficial for moderate climate change".

Professor Tol was one of the Coordinating Lead Authors on the chapter, so I contacted him and other members of the IPCC to alert them to the defects.

When the final version of the report's chapter was published in October 2014, the mistakes had been corrected and it omitted the erroneous suggestion that moderate warming would create net economic benefits for the world.

In May 2014, the Journal of Economic Perspectives published a 'Correction and Update' by Professor Tol, acknowledging some, but not all, of the flaws in his 2009 paper. The journal shortly afterwards published another version of the 'Correction and Update', noting that the previous version had still been incorrect, but it also contained mistakes. I contacted the journal to point out that further corrections were required, but I was only offered the option of leaving an online comment.

The new 'Editorial Note' in the journal was written after "the editors discussed the situation with Richard Tol and with outside reviewers at some length". It admits that the 'Update and Correction' produced by Professor Tol "also contained errors that were soon pointed out by various researchers". It also highlighted shortcomings in the trend that Professor Tol had fitted to the data.

This is just the latest shocking development in a sorry saga that has lasted for more than a year, during which Professor Tol has repeatedly criticised me for pointing out the errors in his work.

He even persuaded The Mail on Sunday newspaper to publish in April 2014 an article attacking me.

But two of Professor Tol's papers have still not been fully corrected, and The Spectator has not withdrawn the flawed article by Viscount Ridley.

It is to be hoped that this final verdict from the journal draws to a close an episode that has become an embarrassment not just to climate change 'sceptics', but also to the academic economics profession.

Bob Ward is policy and communications director at the ESRC Centre for Climate Change Economics and Policy and the Grantham Research Institute on Climate Change and the Environment at London School of Economics and Political Science.