There has been an unusual surge of interest in the climate sensitivity based on the last decade’s worth of temperature measurements, and a lengthy story in the Economist tries to argue that the climate sensitivity may be lower than previously estimated. I think its conclusion is somewhat misguided because it missed some important pieces of information (also see skepticalscience’s take on this story here).
While the Economist referred to some unpublished work, it missed a new paper by Balmaseda et al. (2013) which provides a more in-depth insight. Balmaseda et al suggest that the recent years may not have much effect on the climate sensitivity after all, and according to their analysis, it is the winds blowing over the oceans that may be responsible for the ‘slow-down’ presented in the Economist.
It is well-known that changes in temperature on decadal time scales are strongly influenced by natural and internal variations, and should not be confused with a long-term trend (Easterling and Wehner, 2009;Foster and Rahmstorf, 2011).
An intensification of the trades has affected surface ocean currents called the subtropical gyres, and these changes have resulted in a predominance of the La Nina state. The La Nina phase is associated with a lower global mean temperature than usual.
Balmaseda et al’s results also suggested that a negative phase of the pacific decadal oscillation (PDO) may have made an imprint on the most recent years. In addition, they found that the deep ocean has warmed over the recent years, while the upper 300m of the oceans have ‘stabilised’.
The oceans can be compared to a battery that needs to be recharged after going flat. After the powerful 1997-98 El Nino, heat flowed out of the tropical oceans in order to heat the atmosphere (evaporative cooling) and the higher latitudes. The warming resumed after the ‘deflation’, but something happened after 1998: since then, the warming has involved the deep ocean to a much greater extent. A weakening of the Atlantic meridional overturning circulation (MOC) may have played a role in the deep ocean warming.
The recent changes in these decade-scale variations appear to have masked the real accumulation of heat on Earth.
The new knowledge from this paper, the way I read it, is the revelation of the role of winds for vertical mixing/diffusion of heat in a new analysis of the world oceans. Their results were derived through a set of different experiments testing the sensitivity to various assumptions and choices made for data inclusion and the ocean model assimilation set-up.
The analysis involved a brand new ocean analysis (ORAS4; Balmaseda et al., 2013) based on an optimal use of observations, data assimilation, and an ocean model forced with state-of-the-art description of the atmosphere (reanalyses).
By running a set of different experiments with the ocean model, including different conditions, such as surface winds and different types of data, they explored which influence the different conditions have on their final conclusion.
The finding that the winds play a role for the state of the warming may not be surprising to oceanographers, although it may not necessarily be the first thing a meteorologist may consider.
Other related discussions: OSS
References
- M.A. Balmaseda, K.E. Trenberth, and E. Källén, "Distinctive climate signals in reanalysis of global ocean heat content", Geophysical Research Letters, vol. 40, pp. 1754-1759, 2013. http://dx.doi.org/10.1002/grl.50382
- D.R. Easterling, and M.F. Wehner, "Is the climate warming or cooling?", Geophysical Research Letters, vol. 36, 2009. http://dx.doi.org/10.1029/2009GL037810
- G. Foster, and S. Rahmstorf, "Global temperature evolution 1979–2010", Environmental Research Letters, vol. 6, pp. 044022, 2011. http://dx.doi.org/10.1088/1748-9326/6/4/044022
- M.A. Balmaseda, K. Mogensen, and A.T. Weaver, "Evaluation of the ECMWF ocean reanalysis system ORAS4", Quarterly Journal of the Royal Meteorological Society, vol. 139, pp. 1132-1161, 2012. http://dx.doi.org/10.1002/qj.2063
Magns W & sidd @ 198/199.
The Transient Contrarian Response, as expected, is high when there is any mention of climate sensitivity being not as high as it might be. (I think it has some sort of inverse-square relationship.)
One of the takes on planet Wattsupia for instance, is titled New paper shows transient climate response less than 2°C. Given IPCC AR5 use a central TCR figure of 1.9°C, this title hardily heralds stunning revelations, or indeed justification for the conclusion reached. “The take-home message from this study … is that the … IPCC AR5 … ECS and … TCR … are out of line with instrumental-period observational evidence.
Of course, we cannot expect those on Wattsupia to be bothered by such misrepresentation of a single scientific paper when they delight in mashing the totality of science.
The paper’s lead author describes his findings thus – “Recent observations suggest the expected rate of warming in response to rising greenhouse gas levels, or ‘Transient Climate Response,’ is likely to lie within the range of current climate models, but not at the high end of this range. However, with current emissions trends, this would lead to very high temperatures to the end of the 21st century.
“The eventual long-term warming after stabilization remains rather uncertain, but for most policy decisions, the transient response over the next 50-100 years is what matters.”
Three further authors from the paper also give their comment here, ‘here’ being somewhere that is mindful of presenting a reliable and honest account of the paper, unlike on Wattsupia and those other the planets in the deniosphere.
Alexander Otto Artcle on the Met Office site
http://www.metoffice.gov.uk/research/news/alex-otto-article
From the article:
“The 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 ”
Think the ecs is used in e relevant way… but not enough time is put on trying to explain problems with the studie and how it relates to eg. paelo records.
Balmaseda et al’s proposal that trade wind intensification may help to explain the distribution of ocean heat content trends with depth may not fully apply to the strongest feature in their map (fig. S06) of heat content trends below 700 m during the years 2000 to 2009. That feature, in the East of the Atlantic has the morphology of a plume at about 40 deg North latitude. In the Atlantic, trade winds have weakened recently. http://www.sciencedaily.com/releases/2011/02/110206132902.htm
Since the Mediterranean outflow current inhabits this region and depth, a change in its characteristics might explain this feature. Since the waters of the Mediterranean have been getting both warmer and saltier, http://www.livescience.com/6510-mediterranean-sea-saltier-hotter.html the needed change is in the correct direction.
A strip of rising heat content within about 15 deg of the Equator may well be related to trade winds (integrated within 30 deg of the Equator in their fig.S04) but rather a lot is going on outside of the tropics. Comparing the sea surface temperature trends for 2000 to 2009, http://data.giss.nasa.gov/cgi-bin/gistemp/nmaps.cgi?year_last=2013&month_last=4&sat=-1&sst=3&type=trends&mean_gen=0112&year1=2000&year2=2009&base1=1951&base2=1980&radius=250&pol=reg at least the coastal cooling for North America might be associated with the warming trend below 700 m to the west through the Bakun mechanism discussed above. Some of the structure off the coast of Chile may also be consistent with enhanced upwelling, something that was deduced to occur during the 20th century. http://onlinelibrary.wiley.com/doi/10.1029/2006GL028812/abstract Structure of NW Africa, does not seem have to such a pattern in 2000-2009 as it did prior to that. http://www.ncbi.nlm.nih.gov/pubmed/17272719
There are also a number of structures near Antarctica in fig. S06 that could be associated with wind or with other sources of vertical flows. Still, in keeping with the folk song theme of this post I’d say “Down in the basin, the basin so low, turn those layers over and hear the wind blow.”
In the current situation, where the north is heating and the south is not, if the sea level rises that means the global ice quantity is INCREASING. Why ?
Most of the north pole ice is made of pack ice which is floating – exactly like an ice cube – on the ocean : the only way to get it make the ocean rise is to put more ice on it (when it melts, nothing happens to the sea level)
On the South pole, it is the opposite, most of the ice is on the earth, and we know it is globaly not melting yet.
The only other alternative would be because thermal dilatation of the waters but certainly not because of ice melting.
I’m wondering if Balmaseda et.al. 2013 Distinctive climate signals in reanalysis of global ocean heat content takes data from below 2000m into account. The paper repeatedly refers to heat storage “below 700m” as a class of data but puts no lower depth limit on it.
Balmaseda et.al. cite Levitus et.al. 2012 World ocean heat content and thermosteric sea level change, and Kouketsu et.al. 2011 Deep ocean heat content changes estimated from observation and reanalysis product and their influence on sea level change.
Levitus rejects concluding something about what’s happening below 2000m saying “we simply do not have enough… data from depths exceeding 2000m available to ascertain if there is a contribution from this layer”.
Levitus et.al. acknowledges the Kouketsu et.al. attempt: “If the results of Kouketsu et.al.[2011] are correct, this would mean a contribution of 1.6×10 to the 22nd power J from the ocean region in the 3000m – bottom layer”. Balmaseda et.al. total ocean heat content to 2009 appears to be about 20×10 to the 22nd power J. which I take it means Levitus et.al could be ignoring 8% or so of the heat accumulating in the ocean.
Levitus et.al. are careful to describe what they are talking about as the ocean in the 0 – 2000m layer.