Over the last few weeks, I have been engaged to a series of exchanges on the weblogs Skeptical Science and Real Climate. In this post I want to summarize the science issues that were discussed on Real Climate particularly with Gavin Schmidt. I will post separately on my interactions on Skeptical Science in the next few days.
In terms of Real Climate, in their post
The comments and replies by Gavin Schmidt (and others) on the Real Climate post subsequent to my above weblog post are informative. I have reproduced several below.
The main conclusion I have reached from the series of comments/replies are:
1. The ocean heat content change is the robust methodology to diagnose global warming and cooling.
2. To provide the most robust measure of the heating and cooling, the heat at levels below 700m needs to be considered.
3. The odd sudden increase in heating in about 2004, whereas none was reported previously, is very puzzling. It appears just in time to explain the relatively small heating in the upper 700m. Does this mean the physical response of the ocean to heating has changed, or is it a data issue?
4. There remains a lack of clarity as to whether Argo can track heat if it transfers through the upper 700m into the deeper depths. There is no doubt, however, that if this heat is from the TOA radiative imbalance (i.e. from added CO2 and other greenhouse gases) the heat must travel through this layer. Gavin Schmidt has stated that “Heat transfer will be mainly continuous, not episodic”. I challenged him to support this conclusion.
5. Currently, in the Argo network, there are roughly 3000 floats producing 100,000 temperature/salinity profiles per year. The floats go as deep as 2000m. If heat is transported on shorter time periods through the entire upper 700m, than it could be missed in the sampling. However, if the transport is slower than can be sampled with ~33 profiles per year (~ once every 11 days) than it will be sampled. Analyses such as provided by the ECMWF suggest the transfers are not continuos as Gavin concludes but are in globs; e.g. see http://www.ecmwf.int/products/forecasts/d/charts/ocean/real_time/xzmaps/
Roger A. Pielke Sr. says:
Gavin – I am glad you noticed my post
Torpedoing Of The Use Of The Global Average Surface Temperature Trend As The Diagnostic For Global Warming
We seem to disagree on several points. First, you write
“The second point is related to a posting by Roger Pielke Sr last week, who claimed that the Meehl et al paper ‘torpedoed’ the use of the surface temperature anomaly as a useful metric of global warming. This is odd in a number of respects. First, the surface temperature records are the longest climate records we have from direct measurements and have been independently replicated by multiple independent groups. I’m not aware of anyone who has ever thought that surface temperatures tell us everything there is to know about climate change, but nonetheless in practical terms global warming has for years been defined as the rise in this metric. It is certainly useful to look at the total heat content anomaly (as best as it can be estimated), but the difficulties in assembling such a metric and extending it back in time more than a few decades preclude it from supplanting the surface temperatures in this respect.”
However, we now have a robust way to diagnose upper ocean heat content, we should move to that metric, starting in ~2003, as the primary metric to monitor global warming.
[Response:The idea that there can be only one metric has no basis in anything. Every new stream of information is useful in building up a picture of what is happening – some records have longevity, others have depth, some are regional, some are global. Your desire to dethrone or torpedo the global surface temperature records is merely rhetorical (unless you are seriously suggesting that we stop monitoring the surface temperatures? Surely not!). – gavin]
Also, NASA, GISS and CRU analyze their data differently, but they have a large overlap in their raw data; see my post
Erroneous Information In The Report “Procedural Review of EPA’s Greenhouse Gases Endangerment Finding Data Quality Processes”
[Response:More semantics: – the *analyses* of the raw data are independent, and it is easy to show that you get the same basic trend with completely independent subsets of the data. – gavin]
“the surface temperature records …. have been independently replicated by multiple independent groups”.
This is not correct.
[Response: Yes, it actually is. And the Berkeley effort will show it again. – gavin]
Finally, you write
“Obviously heat going below 700m must have passed through the upper ocean. However, the notion that Argo could see this is odd. Argo measures temperature, not flux. The net flux into a layer is calculated by looking at the change in temperature. It cannot tell you how much came in at the top and left at the bottom, only how much remained. – gavin]”.
You are, of course, correct that Argo measures temperatures, but unless you can show the temporal sampling period is too long, or the spatial sampling is too sparse, the downward movement of heat would be seen in positive temperature anomalies as they move towards lower depth. Similarly, if this heat were to re-emerge, we would also see it as the anomalies move upwards.
[Response: This is a continuous process – not lumps of anomalous heat that can be tracked individually. – gavin]
Also, if there is large amounts of heat being stored at depth in the ocean, this means that the global annual average surface temperature trend is not sampling this heat. This surface temperature trend would be underestimating global warming.
[Response:Semantics: You are redefining ‘global warming’ to something different to what anyone else thinks and then claiming that the standard measure of global warming (as understood by everyone else) is not being properly sampled. I can redefine apple to mean an orange, and then claim that people shouldn’t just bite into apples because of the skin. It might make sense logically, but as a method of communicating a fact to an audience, it is woeful. Words do not mean just what *you* say they mean. – gavin]