by Judith Curry

New research suggests that the upper layer of the ocean has warmed more than had been thought previously while the deeper ocean has cooled rather than warmed in recent years.

Context

Kevin Trenberth summed up the problem in his famous statement that it’s a “travesty” that we can’t find the missing heat. Climate scientists have been inferring (mainly from models) that the missing heat (during the pause) is hiding in the deep ocean. For background, see these previous Climate Etc. posts:

Two new papers have just been published in Nature Climate Change:

Deep-ocean contribution to sea level and energy budget not detectable over the past decade

W. Llovel, J. K.Willis, F.W. Landererand and I. Fukumori

Nature Climate Change. DOI: 10.1038/NCLIMATE2387 [link]

Abstract. As the dominant reservoir of heat uptake in the climate system, the world’s oceans provide a critical measure of global climate change. Here, we infer deep-ocean warming in the context of global sea-level rise and Earth’s energy budget between January 2005 and December 2013. Direct measurements of ocean warming above 2,000m depth explain about 32% of the observed annual rate of global mean sea-level rise. Over the entire water column, independent estimates of ocean warming yield a contribution of 0.77 +/- 0.28mmyr-1 in sea-level rise and agree with the upper-ocean estimate to within the estimated uncertainties. Accounting for additional possible systematic uncertainties, the deep ocean (below 2,000 m) contributes -0.13+/- 0.72mmyr-1 to global sea-level rise and -0.08 +/- 0.43Wm2 to Earth’s energy balance. The net warming of the ocean implies an energy imbalance for the Earth of 0.64 +/- 0.44Wm-2 from 2005 to 2013.

Quantifying underestimates of long-term upper-ocean warming

Paul J. Durack, Peter J. Gleckler, FelixW. Landerer and Karl E. Taylor

Nature Climate Change DOI: 10.1038/NCLIMATE2389 [link]

Abstract. The global ocean stores more than 90% of the heat associated with observed greenhouse-gas-attributed global warming. Using satellite altimetry observations and a large suite of climate models, we conclude that observed estimates of 0–700 dbar global ocean warming since 1970 are likely biased low. This underestimation is attributed to poor sampling of the Southern Hemisphere, and limitations of the analysis methods that conservatively estimate temperature changes in datasparse regions.We find that the partitioning of northern and southern hemispheric simulated sea surface height changes are consistent with precise altimeter observations,whereas the hemispheric partitioning of simulated upper-ocean warming is inconsistent with observed in-situ-based ocean heat content estimates. Relying on the close correspondence between hemispheric-scale ocean heat content and steric changes, we adjust the poorly constrained Southern Hemisphere observed warming estimates so that hemispheric ratios are consistent with the broad range of modelled results. These adjustments yield large increases (2.2–7.1 1022 J 35 yr-1) to current global upper-ocean heat content change estimates, and have important implications for sea level, the planetary energy budget and climate sensitivity assessments.

Durack has a very good web site with lots of supplemental info and diagrams.

Reporting Climate Science

Reporting Climate Science has a good article covering both papers Scientists Find Clues to Missing Energy. Excerpts:

The implication of this is that a build up of heat in the deep oceans is not the solution to the so called missing energy mystery that has puzzled climate scientists trying to match the observed heat build up on the planet with what the theory of global warming suggests should be happening. A number of climate scientists had previously suggested that heat is accumulating in the deep oceans and that this accounts for the missing energy.

An analysis of ocean data together with satellite measurements suggests that the warming rate for the top 700m of ocean in the southern hemisphere has been underestimated – at least from 1970 until the early 2000s when an array of measurement buoys, known as Argo, began to collect data.

Separately, an analysis of satellite measurements and ocean temperature data has revealed that that the deeper half of the ocean (below 2 km depth) has, on average, not warmed from 2005 to 2013 and may have cooled – in contrast to the prevailing view, based on sparse ship-based measurements, that had suggested deep ocean warming between the 1990s and 2005.

Papers relating to both pieces of research have been published in Nature Climate Change. Both papers are important because they shed light on the debate around the so called missing energy mystery. Essentially, they imply that heat has accumulated faster than had been thought in the upper ocean but not, as many have suggested, in the deeper ocean below 2km.

A team led by Paul J. Durack of the Lawrence Livermore National Laboratory in the US found that models of sea level rise agree with observations but that the warming of the upper ocean predicted by these models did not agree with observations; particularly in the southern hemisphere.

They inferred from this that upper ocean warming rates in the southern hemisphere have been underestimated – that it was the previous observations that were inaccurate and that the models were correct. This would imply that the that during the period from 1970 to 2000 the Earth was absorbing between 0.04–0.13 Wm-2 more than previously estimated, they say.

A second group led by William Llovel of the Jet Propulsion Laboratory in the US used satellite radar altimetry data to determine that sea level has been rising at a global average rate of 2.78 mm yr–1from 2005 to 2013. Over that period, ocean expansion from warming in the upper 2 km has accounted for 0.9 mm yr–1of that rise, according to in situ ocean measurements, and transfer of freshwater into the ocean 2.0 mm yr–1, according to satellite measurements of Earth’s changing gravity field.

This adds up to 2.9mm yr-1 which is more than has been seen overall – implying that an offsetting decrease is taking place due to cooling in the deep oceans. The residual of those numbers implies a deep ocean cooled rather than warmed in the period from the 2005 to about 2013 and that this cooling equivalent to a decrease in sea level of −0.13 mm yr–1.

The significance of this result is that it implies that the so called missing energy is not to be found in the deep ocean as many climate scientists have suggested. The team publish their results in a paper entitled “Deep-ocean contribution to sea level and energy budget not detectable over the past decade”.

JC reflections

Both papers indeed present clues related to ocean heat content and the missing heat, but there are substantial uncertainties associated with both analyses.

I think the Lloverl paper is important, in terms of attempting to reconcile available temperature and sea level rise measurements within the uncertainties, but the uncertainties are pretty substantial.

The Durack et al. paper has implications for ocean uptake in estimates of climate sensitivity (as per the methodology used by Lewis/Curry).

The bottom line is that uncertainties in ocean heat content are very large, and there is no particularly convincing evidence that the ‘missing heat’ is hiding in the ocean.