A revised estimate of the processes contributing to global warming due to climate-carbon feedback

[OKIsItJustMe]

My apologies (in advance) if this was already posted, I checked back, and did not see it:

http://www.agu.org/pubs/crossref/2009/2009GL038681.shtml

A revised estimate of the processes contributing to global warming due to climate-carbon feedback

P. Cadule
LSCE, IPSL, CEA, CNRS, Gif-sur-Yvette, France
IPSL, UPMC, Paris, France

L. Bopp
LSCE, IPSL, CEA, CNRS, Gif-sur-Yvette, France

P. Friedlingstein
LSCE, IPSL, CEA, CNRS, Gif-sur-Yvette, France
QUEST, Department of Earth Science, University of Bristol, Bristol, UK

Coupled climate-carbon cycle models have shown that anthropogenic climate change has a negative effect on natural carbon sinks i.e., climate change induces a reduction in both land and ocean carbon uptake leading to an additional amount of CO2 in the atmosphere. Friedlingstein et al. (2006) concluded that such supplementary CO2 in the atmosphere would lead to an additional climate warming in 2100. However, as given by Friedlingstein et al. (2006), the role of non-CO2 greenhouse gases (GHGs) and aerosols was neglected both for their direct impact on climate and their indirect impact on the carbon cycle. Besides, the climate models used for IPCC AR4 accounted for the radiative forcing of all GHGs and anthropogenic aerosols but neglected the climate-carbon cycle feedback. In IPCC AR4, Meehl et al. (2007) attempted to reconcile these two methods in order to derive the global warming that would arise from both all anthropogenic forcings and climate-carbon cycle feedback. Here we show that the approach they used is wrong for several reasons. First, as previously done by Friedlingstein et al. (2006), they considered that the warming is proportional to the change in atmospheric CO2 concentration. This assumption leads to consider that the gain in temperature is equal to the gain in CO2. However, because of the non-linearity of the climate response to increased CO2 concentrations, the gain in temperature is lower than the gain in CO2. Second, they assumed that the temperature gains of the climate-carbon cycle feedback generated by CO2, non-CO2 GHGs and aerosols are all equal. We show here that, because of the specific spatial and temporal distribution of the radiative forcing exerted by those external perturbations, the temperature gains are all different. Based on our revised method, we found that, for the SRES A2 scenario, the projected global warming in 2100, due to increases in atmospheric CO2, non-CO2 GHGs and anthropogenic sulphate aerosols, is 2.3–5.6°C. This is accidentally nearly equal to the original one of Meehl et al. (2007) (2.4–5.6°C).

---

Received 16 April 2009; accepted 5 June 2009; published 25 July 2009.

Citation: Cadule, P., L. Bopp, and P. Friedlingstein (2009), A revised estimate of the processes contributing to global warming due to climate-carbon feedback, Geophys. Res. Lett., 36, L14705, doi:10.1029/2009GL038681.

[GliderGuider]

1. They seem to be saying

Despite the methodology being wrong, wrong, wrong, the conclusions were right, right, right...

That tells me that we're converging on an accurate estimate for the temperature rise -- slight changes in methodology aren't making any major difference to the outcome.

[OKIsItJustMe]

2. Yes, the earlier conclusions appear to be correct (if for the wrong reasons)

If I'm reading it right, as time progresses, the other method would have greater and greater error, but, geologically speaking, 100 years is nothing.

(A curve approximates a straight line, if you look at a small enough piece of the curve.)

[Nederland]

3. Agreed

The predicted 2.3–5.6°C range is in line with all the consensus science on climate change. I would also agree that it appears that we are converging on an accurate estimate for the temperature rise. I would also point out however, that the 2.3–5.6°C figure is lower than many of the outlier predictions that get posted around here, along with ridiculous predictions of 20+ ft sea level rises. All in all, a 2.3–5.6°C rise spread out over a 100 year period is one that can be dealt with fairly easily.