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Stern Science

Filed under: — group @ 28 January 2007 - (Français) (Português)

Halldór Björnsson, William Connolley and Gavin Schmidt

Late last year, the UK Treasury’s Stern Review of the Economics of Climate Change was released to rapturous reception from all sides of the UK political spectrum (i.e. left and right). Since then it has been subject to significant criticism and debate (for a good listing see Rabbett Run). Much of that discussion has revolved around the economic (and ethical) issues associated with ‘discounting’ (how you weight welfare in the future against welfare today) – particularly Nordhaus’s review. We are not qualified to address those issues, and so have not previously commented.

However, as exemplified by interviews on a recent Radio 4 program (including with our own William Connolley), some questions have involved the science that underlies the economics. We will try and address those.

Unlike an earlier report by the House of Lords, Stern spends no time quibbling, and essentially takes the science from the IPCC report, though somewhat updated by more recent work. Most of the science is flipped through fairly quickly within chapter one, and casual readers familiar with the IPCC report will find little to surprise them with sections including statements such as “An overwhelming body of scientific evidence indicates that the Earth’s climate is rapidly changing, predominantly as a result of increases in greenhouse gases caused by human activities” etc. However, the scientific possibilities in Stern are weighted slightly differently than in the IPCC reports since, as he states, “policymakers need to take into account the risks of greater dangers, as well as central expectations, because the consequences if these risks were to materialise would be very serious” (Stern reply to Byatt et al).

There are three strands to the science in Stern: the climate sensitivity, future emissions of greenhouse gases and the impacts of any particular level of change (scaled to the global mean temperature anomaly for convenience).

The climate sensitivity (as discussed here previously) was given a likely range of 1.5 – 4.5 C in IPCC TAR, and with a range of 2 – 5 C in the models used in that report. However, the probability of higher values plays a significant role in the report. Specifically, Meinshausen (2006) that there is “between a 2% and 20% chance that climate sensitivity is greater than 5C” but in the key message section of chapter 1 this is distilled as: “Several new studies suggest up to a 20% chance that warming could be greater than 5C”. This is true, but the report neglects to mention other new studies (Annan and Hargreaves; Hegerl et al) that suggest a negligible probability of CS greater than 5 C.

Uncertainty about future warming is not just the uncertainty about sensitivity, but also about the future greenhouse gas levels (GHG). There is a wide range of scenarios and estimates of future GHG levels that are used in the IPCC reports. The scenario used by the Review is the A2 one, but in this scenario GHG in the latter part of the 21st century is higher than in say, the A1b scenario. The point here is not that A2 is less sound than the A1b scenario, but simply that the Review chooses to work with one of the “high emission” scenarios. Additionally, the report also acknowledges the highly uncertain (but not clearly quantifiable) the possibilities of positive feedbacks in natural CO2 and CH4 emissions.

For impacts of climate change the story is similar: many of the impacts mentioned possible but their likelihood is debatable. For example, the weakening of the THC under 1 degree of warming, a risk of collapse for 3 degrees, risk of irreversible melting of the Greenland Ice sheet at 2 degrees warming, sea level changes of 5 – 12 meters over several centuries, – these eventualities are debatable, and should certainly be viewed as the “adverse tail” of possible impacts.

In conclusion: Stern gets the climate science largely right, though he strays on the high side of various estimates and picks the high side to talk about in the summary. This high-end bias lends the Review open to charges of “alarmism”. The report does make the fair point that the damages and their cost grows disproportionally with increasing temperature change and so, given that asymmetry, policymakers are correct in taking note of them. However, it looks like the major criticism of his work will be directed (in other fora) at the economics.

NB. Rather predictably, some of the usual contrarian suspects have also attacked the science in Stern. It is, however, a measure of their fundamental lack of seriousness that when there really are important uncertainties (i.e. the likelihood that climate sensitivity is higher than generally thought), they ignore them in favour of making the same repetitive uninteresting and incorrect claims they always make.

*Meinshausen, M. (2006): ‘What does a 2C target mean for greenhouse gas concentrations? A brief analysis based on multi-gas emission pathways and several climate sensitivity uncertainty estimates’, Avoiding dangerous climate change, in H.J. Schellnhuber et al. (eds.), Cambridge: Cambridge University Press, pp.265 280.

55 Responses to “Stern Science”

  1. 51
    Hank Roberts says:

    Bogus. That’s from the 1950s, an atomic bomb “duck and cover” school education film.
    I remember seeing it the first time around.

  2. 52
    David Price says:

    The Stern report was flawed in that he is accused of overstating the damage of agw and understaing the costs of dealing with it. It is therfore rightly accused of bieng propagandist. Remember he works for a government which has a history of producing dodgy dosiers. To command public confidence he will have to clean up his act a bit.
    We need a balanced view of the cost/benefit ratio of carbon reduction. Only this will carry the public with it.

  3. 53
    Dan says:

    re: 52 and “the costs of dealing with (AGW)”. The fact is that business has an absolutely miserable record and very little credibility if any re: estimating the costs of reducing pollution. And by “miserable”, I mean by spreading fear by far over-estimating costs both to business and to the economy. For example, in the US, each time the Clean Air Act has been amended since 1972, fossil-fuel power companies and their associated think-tanks screamed bloody murder that sulfur dioxide and nitrogen oxide emission reductions would essentially destroy the economy (all but ignoring the obvious health and environmental benefits that did come to fruition). Far from it. In fact, after the Clean Air Act Amendments of 1990, the economy grew quite well across the board. Additional mandated or voluntarily implemented controls of other pollutants since 1972 (the year of the “first” US so-called “Clean Air Act”) have also not brought the economy down. Recessions that occurred during the period were due to other unrelated issues/factors. In hindsight, after the 1990 Amendments, it was the US government’s cost estimates that proved to be much more accurate than business estimates.

  4. 54
    SolarNTrains says:

    #49, matt, I am glad to see there are a few pragmatists here. I always find it unfortunate when the Davids and Al denigrate the industrial technologists and scientists, b/c that is who we need to help us pull the wood out of the fire, so to CO2 speak. And a lot them are conservative as well (or NeoCon mouthbreathers, as they are usually referred to by the realclimatorati). If you actually look at some of the studies on alternative energy, we have a long way to go just to keep up with growth, must less replace some of the current sources. I work with solar, and even with the spectrum conversion improvements, we will be lucky if it provides 9% of our energy needs in the next decades. So nukes are probably a necessity, unless you intend to give up economically unnecessary activities (like blogging) or ecologically bankrupt geographical areas (like Southern California).

  5. 55
    SolarNTrains says:

    re: #53; Dan, can’t comment on your opinion here, as I haven’t seen the data. However, I would expect there will always be a diversity of opinion between government and business. In fact, I would be concerned if they agree, and would really want to hold onto my wallet tightly!
    Businesses will be concerned first and foremost with profits, cash flow, expenses, employment, et cetera on a forward looking (and continually reviewed) basis. Governments, except during elections years, tend to be more collection focused (both information and taxes!). Usually, the government only responds when a majority of opinion means it is a popular decision. Thus, I would expect we will finally get a productive response from Congress on Kyoto this year.