Confusion over climate costs undermined IPCC message

Image of scientists bickering with Richard Tol weakened public perception of consensus within IPCC

Source: Benson Kua

Source: Benson Kua

By Gerard Wynn

Confusion about the economic costs of climate change undermined a straightforward message on the risk of severe impacts and the resulting urgency to cut carbon emissions, in a report by the UN climate panel last week.

The Intergovernmental Panel on Climate Change (IPCC) last week documented the risks from climate impacts such as droughts, floods and rising sea levels, including economic costs.

On Sunday, the IPCC publishes a follow-up report on how to cut greenhouse gas emissions.

Together, the reports find that climate impacts will be severe unless the world takes urgent action to cut emissions. Uncertainty about the size of the economic impact of climate change, in monetary terms, has undermined that simple message, however.

One of the biggest controversies has been the view of and publicity given to Sussex University’s Richard Tol, who found that the economic costs were “relatively small”, and described a balance of positive and negative climate impacts.

The IPCC partly contributed to the weight given to Tol’s view, by appointing him co-lead author of the chapter on economic impacts in last week’s report, even though the evidence clearly shows that he is far from the mainstream.

An impression of scientists bickering over the central message of the report, partly as a result of Tol’s contrary views and his senior IPCC role, contributed to public confusion and disengagement, according to media analysts.


Economists take a number of steps when measuring the economic cost of climate change.

They consider the physical damage that may be caused by future climate change, assess how much that would cost, and then quantify those costs in today’s money, taking into account, for example, how much richer people may be in the future.

Experts writing in this week’s issue of the journal Nature considered that such economic assessment was a worthy discipline, by helping policymakers understand the importance of cutting emissions.

“This ‘social cost of carbon’ represents the money saved from avoided damage, owing to policies that reduce emissions of carbon dioxide” they said.

But the calculations have limitations. They have a poor ability to account for uncertainty, including so-called non-linear effects where damage may suddenly increase or accelerate above a certain level of global average warming, for example as a result of sudden collapse of an ice sheet, leading to much higher sea level rise.

In addition, they may be unable to price knock-on effects, such as social unrest, war or mass movement of people as a result of food or water shortages.

“The bulk of the literature and arguments indicates that social-cost models are under­estimating climate-change harms,” they said.

They described several reasons why costs were probably underestimates: the models did not take account of the impacts of climate change on productivity (for example due to more frequent heat waves); did not account for a write-off in the value of certain assets (for example due to sea level rise); and did not allow for rising values of resources such as freshwater or dry land.


Richard Tol had a position of huge authority at the IPCC, as a “coordinating lead author” of the chapter in last week’s report describing economic impacts.

However, he was not in the mainstream view, as described in the Nature article, given that he described the costs as rather small, and reserved the possibility that these were overestimates, in an interview with RTCC on Friday.

The fact that he found himself in conflict with non-economists and government representatives in the final drafting of the IPCC report supported the idea that he was not on the centre-ground.

He was disappointed that the IPCC draft report was revised, inserting caveats into his report of the estimated range of economic costs.

“The most important thing is that the methods got in, that the estimate of economic impact is relatively small,” he told RTCC.

“I don’t have a problem with the caveats, in the sense that they’re wrong. The caveats are right, but they (also) apply to the other impacts. We’re talking about uncertain climate change impacts 50 or 100 years from now. The ecological, agricultural, sea level rise impacts are all difficult to estimate, because they’re 50 or 100 years from now.”

Tol said that the uncertainty concerning economic costs could lead to overestimates as well as underestimates.

“It’s true that they’re incomplete. The only way of resolving bias one way or the other is to do more research.”

Another economist expressed surprise with that view.

“The more you include uncertainty, the more you enter disproportionately nasty surprises,” said Dimitri Zenghelis, co-head of policy at the Grantham Research Institute on Climate Change, at the London School of Economics.

“I haven’t seen scientists talking about encountering nice surprises or lovely tipping points. In general, the more you include, the more you’re likely you are to be worried, and the more likely you will want to take action. These (uncertainties) are the variables which make you worry about climate change.”


Tol’s position as co-lead author on economics gave his views more credibility.

He gained media widespread coverage in advance of the publication of the report, with his explosive announcement that he was stepping down from the IPCC writing team because the report was too “alarmist”, as well as in the aftermath of publication, commenting on the findings.

That undermined the report’s message, said one media analyst.

“His view (of the threat and risk) comes across as a reassurance that we don’t have to worry as much about the negative effects,” said Catherine Happer, research associate at the Glasgow University Media Group.

“Richard Tol can be very powerful with that reassuring message. What we find time and again is that the sceptical coverage doesn’t necessarily lead the public to reject the science, but gives the impression of scientists bickering, of less consensus, and disengagement, that we don’t have to worry.”

“It’s sowing the nagging seeds of doubt about whether the science is solid (enough) to act upon. He’s a marginal voice in the IPCC, not to dismiss his claims.”

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