The relationship between global warming and changes in ocean heat content has always been a subject of debate in climate science. This was explicit in Hansen et al, 1997, when he predicted that in the last decades of the twentieth century should not have been a significant increase in ocean heat content (OHC). Note that at the time, no estimate of the observation of change (the first was in 2000 [Levitus et al, 2000]), giving an example of a successful model for climate prediction. In RC, we have followed the issue several times, eg 2005, 2008 and 2010. In recent months, however, a series of new documents in this regard that offer an interesting perspective on the subject that will certainly continue as CMIP5 models begin to be tested.
The most recent book was a new study led by NCAR last week that examined what happens when you have OHC models are occasional periods of 10 years without the development of the world average [Meehl et al, 2011].
And 'know (or at least should be), that the simulations of the late 20 ° C and the beginning of 21 century, do not give a monotonically increasing temperature in a year or ten years time. For the AR4 models, estimates of the expected ten-year trends in the forcings are now roughly N (0.2,0.14) (ie the Gaussian distribution centered on the decade of 0.2 ยบ C / with a standard deviation of about 0.14 ° C / decade . This means that one would expect the probability of 8% to obtain surface temperature trends during a decade less than zero.
Meehl et study examined changes in ocean heat content during these decades of sporadic and comparing the changes seen in recent decades, the positive trend of the surface. What they found was for decades the temperature of the cooling surface was always higher than the average growth rate of ocean heat content. This makes perfect sense, if there is a change in the decades of internal flow, linking deeper than the ocean surface of the ocean (which, of course, there is one). Abnormal heat flow downwards reduces the sea surface temperature (and hence the temperature of the Earth), which produces the abnormal flow of heat from the atmosphere to the sea (the sea because the flow associated with differences in atmospheric temperature and ocean) . And this, of course, is growing throughout the OHC.
A related study of the UK Met. Bureau examined the relationship between changes in ocean heat content in the top 700 and the total ocean heat content changes in the models [Palmer et al, 2011]. They found that (unsurprisingly) there is more variation in the top 700 in the entire ocean. This is important to quantify because we have better estimates of changes in upper ocean that we OHC trends across the ocean. Observational studies show that less than 700m elevations are not trivial - but they are poorly characterized [von Schuckmann et al, 2009]. The study shows that Palmer uncertainty in the decadal change in total OHC is about 0.15 W/m2, if you do change for the CMB than 700m.
So what can we infer about the real world of these tests? First, we can conclude that we look at the right quantities. Total OHC changes are a good measure of the total radiative imbalance. The second is likely to be a systematic problem, if we look at the transformation 0-700m - this is a noisy estimate of the total variation OHC. Third, if the impacts are close to what we expect, we should expect that the deep ocean (below 700m) is to absorb some of the lost ground. Of course there are short-term sources of variability, which also affect these measures (OHC changes associated with ENSO, solar variations over the solar cycle), which complicates the situation.
Two additional points are entered into discussions recent comments related to this. The first is whether changes in ocean heat content of the deep has no direct effect, except for the amortization of the response surface radiation balance according to the present. The deep sea is really huge, even for large changes in OHC, we discuss the profound implications for the temperature is low (I would say less than 0.1 degrees C or so). It is unlikely to have much direct impact on the deep biosphere. And it's not the heat will return from the deep ocean any time soon (the idea that this heat is heat that is "on track" is incorrect). On the contrary, these measures are important for what they tell us about the TOA radiative imbalance, and this is important for future warming.
The second point is related to a posting by Roger Pielke Sr. last week which stated that "torpedoed" Meehl et al paper is used for surface temperature anomaly as a useful measure of global warming. It is strange in many respects. First, the surface temperature record is the longest climate records we have from direct measurements and was repeated independently by several independent groups. I know no one ever thought that the surface temperature tells us everything there is to know about climate change, yet in practice, global warming has for years been defined as an increase in this parameter . It is certainly useful to consider the total heat content anomalies (as good as it can be estimated), but it is difficult to obtain such a metric and extend in time more than a few decades to exclude the temperature surface moved in this regard.
Overall, I believe that these studies show how you can use climate models is at its best. Looking at relationships with key levels - which can be seen in the real world and those that are important for weather - we can use models to interpret what is measured in the real world. In these cases, the conclusions are not particularly surprising, but it is important that they can be measured. Please note that the assumption here is comparable to accept that the real world is more complex than that (imperfect) models, the conclusions in the real world would least trust models tested before applying them in reality.
However, it is true that none of these studies show that these effects are happening in the real world - are only indicative of what we might expect strong.
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