Criticism of
"Copenhagen Consensus on Climate "  2009
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A conference using the "Copenhagen Consensus" setup and dealing with climate issues was held in the first week of September 2009 at Georgetown University in Washington DC. It is presented on this official web site.

The goal of the conference was to answer the question:
“If the global community wants to spend up to, say $250 billion per year over the next 10 years to diminish the adverse effects of climate changes, and to do most good for the world, which solutions would yield the greatest net benefits?”
The Copenhagen Consensus Center commissioned research papers from specialist climate economists, outlining the costs and benefits of each way to respond to global warming. There were eight subjects:
- Geoengineering
- Cutting carbon emissions by taxation
- Protecting and expanding forests
- Cutting emissions of black carbon
- Cutting methane emissions
- Adaptation to climate change
- Research in green energy
- Sharing green technology
For each subject, an expert or team of experts has written an "analysis paper", and other experts have written shorter comments to these, called "perspective papers". All papers were published by the Copenhagen Consensus Center in August 2009. A meeting was then held on September 1st-2nd in Washington DC, with participation of five top economists, three of which are elderly Nobel laureates. They evaluated different methods to cope with climate change, and made a ranking list which was published on September 4th.

The project receiving top priority was a geoengineering project dealing with marine cloud whitening. Other highly prioritzed projects were a technology-led policy of $100b annual investment in energy research&development, another geoengineering project, and adaptation to climate change (e.g. building sea dikes). Bottom priority was given to all proposals putting a carbon tax on fuel.

The results of the conference are presented in the book "Smart Solutions to Climate Change". This is treated in more detail here on Lomborg-errors, where you will find an extensive criticism. A few mainpoints are mentioned here:

General criticism
Two of the experts contributing to the conference, Claudia Kemfert and Roger Pielke, have subsequently raised a fairly harsh criticism of the conference on this web site. They write among many other things: "
The two of us disagree about how best to price carbon . . .  However, we strongly agree that putting a price on carbon is a necessary component in any portfolio of policies designed to decarbonize the global economy."

Comments to the geoengineering proposal
The top priority is a project in which a fleet of boats spray seawater droplets into marine clouds to make them reflect more sunlight. The most extensive criticism of this project is this article written by Alan Robock on the RealClimate web site, here.
A general criticism of geo-engineering is seen here.

Comments to adaptation
The paper on adaptation discusses what happens to estimates of climate damages if adaptation is included in the model runs. A main point is that adaptation, including market-driven adaptation, reduces many potential climate damages to such an extent that it no longer pays to mitigate climate change to any large extent. The results are outcomes from an integrated-assessment-model designed especially to deal with this question, and they depend on how this model is constructed,  which is not very transparent to outsiders.
    The analysis is made by the three Italian economists Carraro, Bosello and De Cian. These are all applied wholly or partially at the Fondazione Eni Enrico Mattei (FEEM), a research institution which is funded by "the ENI group", which is an oil company. One might thus suspect that results from this institution would be biased towards what is favourable or neutral to the oil industry. Actually, the analysis is less biased than many others. But a main problem in the analysis is that damages due to weather catastrophes are left out of consideration; the main damages considered are those to agricultural production and the tourism industry. This makes the estimated damages ridiculously small, and it may make adaptation a more plausible strategy than in real life. Catastrophes are just such events which cannot be counteracted by adaptation. So the paper seems to underestimate the challenge that we are facing.  The perspective paper by Frank Jotzo (also available at the Copenhagen Consensus on Climate web site) is very critical of the analysis paper and should be read as an antidote.

Carbon taxes
The analysis paper by the climate economist Richard Tol is a central paper, because it argues that only very modest taxation of carbon emissions will pay off.
    The paper contains the outputs from a computer model, the integrated assesment model called FUND. The FUND model is fed with five possible schemes for applying carbon taxation. Some of these schemes are, in Tol´s own words, more or less silly, having benefit/cost ratios in the size order of 1/100.
    In one of the schemes, all countries implement a carbon tax of $250/tC in 2010, rising with the discount rate uninterrupted up to the year 2100. This scheme will lead to very low carbon emissions and thus keep temperatures low, but it will be very costly, and a tax at this level seems to be unnecessarily high.
    Another scheme is to set the carbon tax equal to the marginal social cost of carbon (SCC). This is claimed to be $2/tC, and at this level, taxation just pays off, according to the model. However, in the beginning of the analysis paper, Tol presents a metaanalysis of estimates of SCC, and he finds that the median values are at $14/tC or higher, probably more than $20 or $30. This is under those conditions that produce low values; under other conditions, e.g. with respect to discount rates, the values become higher. In another context, Tol has argued that a proper value of SCC is probably about $23-25/tC (see here on Lomborg-errors, comments to page 36 bottom). In an email, I have asked Tol how come that in the modeling part of the paper, he has a SCC of 2 $/tC, whereas in the first part of the paper, he presents SCC estimates that are at least one order of size larger than this. His answer was as follows:
"$2/tC is the SCC in the FUND model, and this was used for the analysis for CCC09. The meta-analysis indeed suggests a SCC that is considerably higher."
That is, the output of the model yields values for the cost of carbon that are at least one size order smaller than any likely estimates in the literature. There is no explanation for this discrepancy. Maybe the value for the climate sensitivity of CO2 used in the model runs could be part of the explanation. In any case, this makes the output of the model of very doubtful value.
    Tol´s paper also contains a review of estimated global costs of  climate mitigation, on the basis of various model runs. The figures presented here are being cited by Lomborg in public debate as `proof´ that reduction of carbon emissions will be very costly. A central sentence in Tol´s presentation is: "Stabilising at 450 ppm CO2eq is needed to have decent chance of keeping temperatures below 2ºC above pre-industrial levels." To this must be said that 450 ppm CO2eq is already below the present level of greenhouse gases in the atmosphere today, which is about 460 ppm CO2eq, and which will eventually lead to an equilibrium temperature rise of probably about 2° C, provided that all cooling sulfate aerosols in the atmosphere will be removed by the fighting of air pollution. From this view of things, it is no wonder that Tol concludes that this will be nearly impossible, and in any case extraordinarily expensive.
   However, some caveats are lacking here. First, if the present composition of the atmosphere could be kept unchanged for a long time, including its content of aerosols, temperatures would be bound to rise by a further 0.6° C up to a level of c. 1.3° C above pre-industrial levels, but not to a level of 2° C (link). Second, the level of CO2 may continue to rise for some time, and still not bring the temperature increase by the year 2100 above 2° C, because there is much lag in the temperature response. The levels of CO2 that cause a temperature increase of 2° C at long-term equilibrium are much lower than those that cause a temperature increase of 2° C already in 2100. If we assume that atmospheric levels of cooling sulfate aerosols will only gradually be reduced, then we need not now reduce to the lvel of 450 ppm CO2eq. We may allow a considerable temporary overshoot, and to allow this may reduce the costs of meeting the 2° goal considerably. In conclusion, the economic costs presented by Tol for meeting the 2° C goal refer to a fairly radical procedure where we immediately reduce atmospheric CO2  to a level that is actually not required immediately, i.e. not before sulfate aerosols have been removed, and not before some point of time after 2100 when the temperature has probably reached its equilibrium. A procedure in which the 2° C goal is kept, but is met via a more moderate route, would infer lower costs. But Lomborg uses the text to state in an authoritative tone that keeping temperature rise below 2° C will be so expensive that it will be stupid to aim at this goal. 


It would not be fair to make only negative comments to the conference contributions. Some of the analysis papers are worth reading, even if one does not agree with all details. Here, I will recommend especially the paper by Galiana and Green: "An analysis of a technology-led climate policy as a response to climate change." The paper warns against overoptimism concerning what technological change may yield, and stresses the danger of non-credible commitments to CO2 reduction targets. It argues that a carbon tax should be introduced; the tax should be low at first, in order that it may be accepted on a global scale, but should rise steadily into the future. Revenue from the tax should be used for public financing of research and development to spur technological innovation. The authors emphasize that reduction commitments that are not based on ready-to-use technological opportunities may be harmful. They might have done more to emphasize the many opportunities that could be realized today at little or no net cost, but still the text is worth reading.