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Matt Ridley's misguided climate change policy

Posted on 23 May 2013 by dana1981

This is a re-post from The Guardian's Climate Consensus – the 97%

In an opinion article for the London Times this past Monday, writer Matt Ridley discussed his interpretation of a new paper which suggests that the Earth's climate sensitivity may be a bit lower than current best estimates. Climate sensitivity refers to the average amount of warming that will occur at the Earth's surface in response to an increased greenhouse effect.

This new paper, led by Alexander Otto at the University of Oxford, suggested that the Earth's surface may warm a bit more slowly than climate models generally indicate. I roughly estimate that about 80% of the warming over the past century would be due to human carbon dioxide emissions, if the results of this study are correct. The good news is that Ridley has accepted the consensus amongst 97% of climate experts that humans are causing global warming and has moved on to examine the consequences.

One of the paper's authors, Myles Allen noted in The Guardian that the results of the study would make little difference with respect to long-term climate change.

"...our new findings mean that the changes we had previously expected between now and 2050 might take until 2065 to materialise instead."

If these results are correct, it would give us perhaps an additional decade or two to get our acts together and dramatically reduce our greenhouse gas emissions. From this news, Matt Ridley concludes that our climate policy is "hopelessly misguided." Those two words may indeed be applied to our climate policy, but Ridley has got it backwards. Or policy is misguided because we're not doing nearly enough to solve the problem.

He suggests, based on outdated references from Bjorn Lomborg, that the economic impacts of climate change are nothing to worry about. Cambridge economist Chris Hope tested this claim by running the climate sensitivity estimates from the new Otto paper in his economic assessment model, PAGE09. The model previously estimated the climate damage from greenhouse gas emissions at an average cost of approximately $100 per tonne of carbon dioxide. The revised estimate resulted in an average cost of $80 per tonne. Given that humans emit over 30 billion tonnes of carbon dioxide per year, that amounts to an annual increase in committed climate change damage of $2.4 trillion, or over 3% of the global gross domestic product, quite contrary to Ridley's rosy perspective.

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Comments 1 to 4:

  1. "committed climate change damage of $2.4 trillion, or over 3% of the global gross domestic product"

    Well, this cost depends on the social discount rate r (among a lot of other variables) the lower the social discount rate, the higher the cost:

    Present value(cost) of pollution = Σ (future damage of year i)/(1+r)i......(summed over i; i is the number of years in the future)

    But the social discount rate is a function of economic growth:

                                                r = δ +γ g,


    • r is the discount rate
    • δ is the so-called "rate of impacience"
    • γ is a parameter called " aversion to intertemporal inequality"
    • g is economic growth

    [source: Christian Gollier, Pricing the future:The economics of discounting and sustainable development, Toulouse School of Economics, 2011]

    δ is set to zero for intergenerational timescales, leaving r as just a function of γ and g.

    Now if the economy is seriously damaged by climate disasters, g will turn smaller, lowering the discount rate and so raising the present value of future damages.

    I don't know how low can the discount rate fall. So:

    Could it fall below zero, making the present value of damages to skyrocket?

    Is this subtle effect accounted when the cost of CO2 is calculated?

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  2. Climate sensitivity is found by the IPCC to be ~3.5C, a value confirmed by paleoclimate studies undertaken by Hansen and others and is widely accepted. Dr Otto et al, using data covering a relatively short period (too short?) has found that sensitivity appears to be significantly lower.

    Ridley concludes from this that public policy on curbing anthropogenic carbon emissions is misplaced, damaging and should be slowed. He comes to this conclusion without accurately quantifying and estimating the effect of slow feedbacks over next 87 years of this century or their capacity to fully off-set the Dr Otto's findings by 2100.

    Those feedbacks include loss of albedo, methane and carbon dioxide emissions trapped in and under permafrost and increased water vapour due to atmospheric warming. Nor can we ignore increasing ocean heat content and the likelihood of its release to the atmosphere, accelerating feedbacks.

    The speed with which feedbacks are now developing is more likely to increase rather than lower the rate of global warming. To interpret the findings of Dr Otto et al as indicating that we may have a decade or so longer in which to curb anthropogenic emissions is, in my view, the height of folly.

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  3. Lomborg is a slippery guy. He hardly claims anything, while conveying the unmistakable message that fossil fuels are all we need, and the environment is doing fine, and why do we have to conserve biodiversity after all?

    He does not say we shouldn't stop deforesting, but he claims that worries about deforesting are grossly exaggerated, and even misrepresents the FAO report to prove it once and for all.

    He does not say global warming is a hoax, but he knows of a climate model that miscalculated how much stratospheric warming there would be and, you know, that's what really matters.

    He does not say we should not manage water resources properly, but he assures us that dessalinization is a definite safety net to dismiss any claims that people would ever endure water shortage.

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  4. To understand skeptics such as Matt Ridley, the best aid is Mark Twain:

    "...There is something fascinating about science. One gets such wholesale returns of conjecture out of such a trifling investment of fact."

    To get the full impact of this statement, see how he prepared the ground at:

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