I'm skeptical whenever the media tries to explain scientific studies in dished out articles, and this would have to be another example for why that is.
http://www.uwe-merckens.com/bilder/Wetter/ngeo.pdfThe most likely value of equilibrium climate sensitivity based on the energy budget of the most recent decade is 2.0 °C, with a 5–95% confidence interval of 1.2–3.9 °C (dark red, Fig. 1a), compared with the 1970–2009 estimate of 1.9 °C (0.9–5.0 °C; grey, Fig. 1a).
A likely value of 2 degrees C is less than the likely value of 3 degrees C from the IPCC, but the range of uncertainty is quite evidently massive from this. It includes a low cut of 1.2 degrees and a high cut of 3.9 degrees. Another small nit to pick is their choice of HADCRUT4, which discounts much of the Arctic, slightly understating the global warming trend compared to the NASA GISTEMP data. Nevertheless, they have a pretty clear caveat:
We note, too, that caution is required in interpreting any short period, especially a recent one for which details of forcing and energy storage inventories are still relatively unsettled: both could make significant changes to the energy budget. The estimates of the effective radiative forcing by aerosols in particular vary strongly between model-based studies and satellite data. The satellite data are still subject to biases and provide only relatively weak constraints (see Supplementary Section S2 for a sensitivity study).
But this point in the TP article is interesting to me:
The researchers say the difference between the lower short-term estimate and the more consistent long-term picture can be explained by the fact that the heat from the last decade has been absorbed into and is being stored by the world’s oceans.
Well, of course. And yet, oceanic behavior is still a large, nagging unknown. Our understanding of ENSO and the PDO in controlling the valves of the ocean's recharge/discharge mechanisms has only become better understood in the last couple of decades. We know that El Niños and warm phases of PDO are associated with warming trends at the surface, but when and how these oscillations move is slippery, as evidenced by last year's El Niño no-show. Other questions loom: What role does the Indian Ocean dipole have on initiating or strengthening an El Niño event, when heat is released to the surface? Are stronger trade winds and a weaker Walker circulation evidence of natural variability or the result of anthropogenic changes? Our understanding of the ocean could not be so disturbingly weak given its importance to our climate. I know scientists have already looked into these questions, but it's clear that many (like Trenberth) lament the general lack of oceanic data.
UPDATE: The topic of climate sensitivity, including synopses of various sensitivity studies in recent years, is discussed in this article of Gavin Schmidt's blog:
http://www.realclimate.org/index.php/archives/2013/01/on-sensitivity-part-i/So, while this particular paper (which I can't read for it has to be purchased) is very probably going to be a welcome addition to the library in the topic of sensitivity, and to be reviewed for its strong points and its flaws by other scientists, I wouldn't stress too much weight on any single study, simply because we have much more to learn. Such is the nature of science.
