What’s the role of the deep ocean in global warming? Climate contrarians get this wrong
Posted on 10 October 2014 by Guest Author This is a re-post from Greg Laden’s Blog
I’ve already posted on a study published in Nature Climate change that shows that the amount of extra global warming related heat in the Southern Oceans is greater than previously thought. There is another paper in the same journal by Llovel et al, “Deep-ocean contribution to sea level and energy budget not detectable over the past decade.” This paper verifies previous research that the oceans absorb a lot of the excess heat, but looks specifically at the ocean below 2,000 meters, which the paper referrs to in places as “deep” but that we should probably call “abyssal.”1 The paper concludes that the abyss is not warming. This is bad news, because if it was warming the total effects of global warming on the surface would be potentially less, or at least, stretched out over a longer period of time. But, it is not unexpected news. We already suspected that the abyssal ocean does not absorb much of the surface heat, while the shallower ocean absorbs quite a bit. Research done prior to 2012 (e.g. Hansen et al 2011) parceled out the energy imbalance the Earth experiences from anthropogenic global warming. The extra heat caused by AGW from 2004 to 2010 was divided among the upper ocean (71%), the deep ocean (5%), with the rest going various other places (only 4% over land). The new paper suggests that the abyssal ocean takes up closer to zero heat. There are three complexities you need to be aware of to interpret this finding. First is the complexity in the climate system, second is the complexity of the research itself, and third is the relatively straight forward statistical problem of assigning meaning to specific numbers. That third one is important for journalists and regular people to pay attention to, because the climate science denial community is already exploiting it to misrepresent this study….So, we have changing quality of data, a data set that is growing incrementally over time, studies that look at slightly different time and space parameters. And, on top of this, we have the increasingly advanced methods of figuring this all out. Both of the Nature Climate Change studies used a combination of direct measurements of temperature at various depths, a measurement of the altitude of the top of the ocean (sea level) from highly accurate satellite instruments, and measures of the mass of the water in the ocean, from the GRAIL gravity research project. If the mass of the ocean stays the same (same number of water molecules) but the surface rises, that is from heat, and that allows an estimate of energy imbalance. If the ocean goes up more than it should from heat expansion, the extra may be from glacial melting. And that is the simple version….But for some reason we see various individuals, including sadly at least one climate scientist (Judith Curry: “Evidence of deep ocean cooling?“), but mostly anti-science climate trolls, crowing that the “deep ocean” is cooling therefore we are not experiencing global warming. However, the truth is that the total amount of heat that is going into the ocean, instead of the atmosphere or other places, was thought to be large, is still known to be large, and in fact is larger than we were originally thinking (from these papers and several others that have come out recently). And, the contribution of the abyss ocean to both sea level rise and energy imbalance is statistically nil. It might be negative, it might be positive, but it is tiny either way. The deep ocean, on the other hand, is in strong positive energy balance.
1The terminology used in this discussion and some of the research papers (or reporting thereof) is a bit confused. Climate scientists have repeatedly said that heat is going into the “deep ocean” and this paper seems to say it is not. But it is. It is a matter of terminology. This is a source of confusion sometimes exploited by climate science denialists. A good way to define these terms is as follows:
Shallow ocean = 0-700 meters
Deep ocean = 700-2,000 meters
Abyss = > 2,000 meters
- Hansen, J., Mki. Sato, P. Kharecha, and K. von Schuckmann, 2011: Earth’s energy imbalance and implications. Atmos. Chem. Phys., 11, 13421–13449, doi:10.5194/acp–11–13421–2011.
- Llovel, W. J. K. Willis, F. W. Landerer, I. Fukumori. 2014. Deep-ocean contribution to sea level and energy budget not detectable over the past decade. Nature Climate Change, 5 October.