IPCC WG3 SPM headline: we can afford it

The Working Group 3 Summary For Policymakers is easily the least readable of the three SPMs released this year:

“In 2030 macro-economic costs for multi-gas mitigation, consistent with emissions trajectories towards stabilisation between 445 and 710ppm CO2-eq, are estimated at between a 3% decrease of global GDP and a small increase, compared to the baseline. However, regional costs may differ significantly from global averages (high agreement, medium evidence).

4 thoughts on “IPCC WG3 SPM headline: we can afford it”

  1. Least readable, huh? I haven’t even finished the WG2 SPM yet (been too busy with work) and I’m even less up to the play with economics than I am with climate science. Couple of queries related to the quoted portion, forgive me if they are answered elsewhwere in the document. Do the baselines used to calculate the GDP cost take into account the economic costs of climate change over the period? If not, are there any estimates of what these costs might be? Also, which scenarios do the stabilisation levels in Table SPM.4 correspond to?

  2. My understanding (and I don’t claim to be an economics whizz) is that the baselines exclude impacts – presumably because of uncertainties over timing and extent. Table SPM 4 refers to the emissions trajectories outlined in Fig SPM 7. These are described as “post TAR” scenarios. It’s complex stuff, which goes a long way to explain why it’s difficult to read! By comparison the earlier SPMs are a picnic.

  3. Thanks. It’s useful to know that a 3% GDP cost is measured against a level that might not be reached anyway – depending on the impacts and when they hit. Time for me to get back to the WG2 SPM to look into that!

    I was trying to get some idea of how the stabilisation scenarios might relate to the WGI SRES scenarios. On revisiting the WGI SPM I notice that “the SRES scenarios do not include additional climate initiatives, which means that no scenarios are included that explicitly assume implementation of the United Nations Framework Convention on Climate Change or the emissions targets of the Kyoto Protocol.” I guess that answers my question.

    Still, it would be nice to get some idea of what kind of climate change we might see over the coming century under the various stabilisation scenarios.

  4. That’s what SPM 4 and SPM 7 in WG3 give you, in effect. A total temperature rise for the end of the century based on various emissions trajectories. But there is a lot of work being done on “peaking” scenarios at the moment. Gavin Schmidt, in this piece at RealClimate suggests Hansen will have a new paper looking at that soon. This sort of projection is directly policy relevant, because it helps to establish the risk attached to any emissions targets.

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