On another thread, John Michelmore has been telling us about an article by Lahouari Bounoua et al (behind the paywall) which finds that the enhanced effect of CO2 on plant growth provides a cooling feedback, so that doubling current CO2 to 780ppm would only cause a temperature increase of 1.64C. Hence we can all relax in relation to global warming mitigation. There’s no need to panic.
Here’s the Science Daily summary.
I haven’t read the article, but would make the following comments. First, it’s one study. Let’s wait to see what others say.
Secondly, it used one model only, and that at the bottom end of the scale. The model used says climate sensitivity is otherwise 1.94C as against the IPCC AR4 range of 2-4.5C. It would be interesting to know why they chose what looks like an outlier.
Third, it’s talking about shorter term “Charney” feedbacks only. An effect of -0.3C on climate sensitivity of 6C would make little difference. Furthermore, subtracting 0.3 from the IPCC range to leave 1.7C to 4.2C. That would not seem to alter the risk of dangerous climate change to any appreciable degree.
Fourth, I find the climate change emanating from the warming we’ve already got unacceptable.
Fifth, I have a bit of a worry that they didn’t take into account the extra warmth from the darker surfaces you’d get by vegetation growing on the Arctic Tundra.
Sixth, We are said to have about 0.6C of warming in the pipeline. It seems they have lost that little bit.
Seventh, in the first item of Climate clippings 6 we saw that the latest on clouds indicates that the cloud effect may raise estimates of climate sensitivity. We are some way from pinning this one down.
Eighth, I have a feeling their results don’t easily fit the paleoclimate record. Hansen reckons that the paleorecord indicates a shorter-term climate sensitivity of 3C, plus of minus 0.5C, with total climate sensitivity increasing as we warm from the current climate state.
It’s not time to put the cue in the rack and spend the next 30 years on business as usual, jawboning about what we might eventually do. There’s no reason for an outbreak of complacency just yet.
As far as I can see, none of the scientific blogs have picked up on this one yet. A pity.