I discussed the papers
C. A. Katsman and G. J. van Oldenborgh, 2011: Tracing the upper ocean’s ‘missing heat’. Geophysical Research Letters (in press).
Palmer, M. D., D. J. McNeall, and N. J. Dunstone (2011), Importance of the deep ocean for estimating decadal changes in Earth’s radiation balance, Geophys. Res. Lett., 38, L13707, doi:10.1029/2011GL047835.
in my posts
I have been sent a summary article from Klimaat wereld on this subject that was published on July 28 2011 [h/t/ Erik].
This Klimaat wereld summary article is titled
by Caroline Katsman and Geert Jan van Oldenborgh, KNMI. Although, as discussed below, I have several issues with their interpretations and conclusions, the authors should be commended for publishing a significant new contribution to our understanding of the climate system. This is an effective paper which can be built on to improve our knowledge of the science of climate.
The abstract reads
“Against expectations, the upper ocean (from 0 to 700 meter depth) has not warmed since 2003. A recent KNMI study shows that an eight-year interruption of the rise expected from global warming is not exceptional. It can be explained by natural variability of the climate, in particular the climate oscillation El Niño in the Pacific Ocean and changes in ocean currents in the North Atlantic Ocean. Recent observations point to an upcoming resumption of the heating of the upper ocean.”
I have extracted several parts of the text of this article [and highlighted text] and comment on them.
“Observations of the sea water temperature show that the upper ocean has not warmed since 2003. This is remarkable as it is expected the ocean would store that the lion’s share of the extra heat retained by the Earth due to the increased concentrations of greenhouse gases. The observation that the upper 700 meter of the world ocean have not warmed for the last eight years gives rise to two fundamental questions:
- What is the probability that the upper ocean does not warm for eight years as greenhouse gas concentrations continue to rise?
- As the heat has not been not stored in the upper ocean over the last eight years, where did it go instead?
These question cannot be answered using observations alone, as the available time series are too short and the data not accurate enough. We therefore used climate model output generated in the ESSENCE project, a collaboration of KNMI and Utrecht University that generated 17 simulations of the climate with the ECHAM5/MPI-OM model to sample the natural variability of the climate system. When compared to the available observations, the model describes the ocean temperature rise and variability well.”
My Comment: If the “question cannot be answered using observations alone“, how can it be stated that “When compared to the available observations, the model describes the ocean temperature rise and variability well“? This is a circular argument. Models themselves are hypotheses, and the more accurate statement by the authors would be that the available observations do not falsify the model as replicating reality.
The next extract reads
“Observations of the temperature of the upper few hundred meters of the ocean go back to the 1960s. Up to ten years ago most measurements were taken by simple thermometers that were thrown overboard and sent back the temperature as they fell down through a wire (expandable bathythermographs, XBTs). Since about ten years these have been superseded by fully automatised ARGO floats that measure temperature down to 2000 m depth and send the data home every ten days. Starting from these raw observations the global temperature distribution down to 700 meter is reconstructed, filling in the gaps in the coverage. Using the heat capacity of water this enables the estimation of the amount of heat stored in the world ocean.”
My Comment: This is a succinct summary of why we need to focus on the observations and model comparisons over the last ten years. Prior to this time period, the values of the ocean heat content are much less certain.
They further write
“In the model, the fraction of negative eight-year trends decrease as the warming trend accelerates, but between 1990 and 2020 (31 years around 2005) 3% of the trends still is negative. This implies a one in three chance of at least one eight-year period with a negative trend in these 31 years. An eight-year pause in the rise of the upper ocean heat content is therefore not at all rare, even in a warming climate.”
My Comment: If the ocean heat warming pauses, this part of the climate system is not warming.
Next, they provide an effective summary of the importance of the ocean as the reservoir for heating and cooling of the climate system.
“Where does the heat go?
The amounts of CO2 and other greenhouse gases in the atmosphere are steadily increasing. The increased absorption of thermal radiation by these gases causes the radiation to space to emanate from higher in the atmosphere on average, where it is colder. The colder air emits less thermal radiation, so that the incoming solar energy is no longer balanced by outgoing radiation. The excess heat is absorbed by the ocean, slowly warming the water from the top down.
If the upper ocean does not warm for a few years the excess heat from the imbalance between incoming and outgoing radiation has to go elsewhere. The ocean temperature has only risen 0.02 ºC less than expected, but due to the size of the ocean and the large heat capacity of water this represents a huge amount of heat. If this heat would have been used to heat the atmosphere, the air temperature would have increased by 5 ºC. This obviously did not happen, so the heat was not stored in the atmosphere. The ground has a larger heat capacity, but heat penetrates only slowly down. Storing the heat missing from the upper ocean in the ground would have raised its temperature by about 1.5 ºC. This also was not observed, so we can conclude that the bulk of the heat did not go into the ground. If the heat would have been absorbed by land or sea ice it would also have had large consequences that have not been detected, for example a sea level rise of 20 cm if the heat would have been used to melt land ice.
By elimination, only two possibilities remain. Either the Earth radiates more energy to space during these periods of no increase in upper ocean heat content or the heat content of the deep ocean (below 700 meter) increases temporarily. Both possibilities were found to play a role in the climate model.”
My Comment: The authors use the “climate model” to explain where the heat goes. However, in the real world, heat that is transported to deeper levels should be seen in the ARGO observations. A further comparison of this tranport, as predicted in the models, with the observations is needed. Moreover, even if there is heat transported to deeper ocean depths, this would mute subsequent atmospheric heating (and, therefore, effects of weather), as the disperion of this heat at depth would be expected to result at most in only a slow transfer back to the surface. The resulting heating of the atmosphere would be muted.
They next write
“The model shows that during periods that the upper layers of the ocean do not heat, the deeper layers show a stronger increase in temperature. This vertical seesaw is strongest in the North Atlantic Ocean south of Greenland. In this area the surface waters cool each winter due to cold winds from Canada. As it gets heavier than the slightly warmer but more salty water at depth the surface water sinks and the warmer water rises. This exchange therefore cools the deeper ocean. In winters with little mixing the upper ocean stays colder and the deeper layers stay warmer.”
My Comment: There is a problem with their statement that “The model shows that during periods that the upper layers of the ocean do not heat, the deeper layers show a stronger increase in temperature”. If the upper layers do not show heating, how does heat transfer (even in the model) to deeper layers? The Joules of heat cannot just appear below the upper 700m if the reason for the assumed heating is from added greenhouse gas forcing in the atmosphere.
They next provide (to their credit) a forecast
“Outlook for the coming years
Since two years ago El Niño has been replaced by a series of La Niña events that should cause a heating trend in the upper ocean. The heat exchange between the upper and deep ocean in the Labrador Sea has also started again recentIy. We therefore expect that the upper ocean heat content will soon resume its upward trend.”
My Comment: First, what is the observational basis to conclude that the “The heat exchange between the upper and deep ocean in the Labrador Sea has also started again recentIy”. Nonetheless, their expectation (forecast) that the upper ocean heat content will resume its upward trend is a hypothesis that can be tested over the next few years [unlike the IPCC type forecasts of weather patterns decades from now!]. As of the most recent upper ocean data analysis, however, the heating has not yet restarted; i.e. see from NODC
It is also important to realize in interpreting this data that for the period before the establishement of the Argo network, the quantitative accuracy of the analyses is less. The data are actually constructed by merging two distinct methods to observe the ocean heat content. The jump seen in the data in the first years after 2000 might have occured due to the temporal inhomogenity of the data analysis.
Finally, they write at the end of their article
“Because of these natural fluctuations a short trend in the upper ocean heat content is not a good indicator of enhanced greenhouse warming, only the long-term trend is.”
My Comment: This is a recognition of the increasingly better recognized importance of “natural climate variations”. However, the authors did not include in their original paper, nor in their Klimaat wereld article how many years of a lack of warming would have to occur before they would reject their models as being skillful replicators of the climate system’s changes in upper ocean heat content.