The only thing we can be sure of about the future is that it will be absolutely fantastic. So if what I say now seems to you to be very reasonable, then I have failed completely. Only if what I tell you appears absolutely unbelievable, have we any chance of visualizing the future as it really will happen.

- Arthur C. Clarke (h/t Brin)

Tuesday, August 4, 2009

Klotzbach et al

An Alternative Explanation for Differential Temperature Trends at the Surface and in the Lower Troposphere

The abstract reads:
This paper investigates surface and satellite temperature trends over the period from 1979-2008. Surface temperature datasets from the National Climate Data Center and the Hadley Center show larger trends over the 30-year period than the lower-tropospheric data from the University of Alabama-Huntsville and Remote Sensing Systems datasets. The differences between trends observed in the surface and lower tropospheric satellite datasets are statistically significant in most comparisons, with much greater differences over land areas than over ocean areas. These findings strongly suggest that there remain important inconsistencies between surface and satellite records.
OK, first of all this is not an abstract, this is a teaser. If the title says "An alternative explanation", the abstract should tell us what it is. Writing as I'm reading, let's see whether the explanation presents itself and is defensible.

We start with an assertion (referencing the CCSP report I discussed yesterday) that "trends in thermometer-estimated surface warming have been larger than trends in the lower troposphere estimated from satellites and radiosondes", a statement which seems to me stronger than is warranted by that report.

However, the possibility that the discrepancy is due to an overestimate in surface trends is not ruled out, and they seem (surprise!) to be gearing up to do so. The discrepancy is most notable in the tropics.
In our current paper, we consider the possible existence of a warm bias in the surface temperature trend analyses
As James pointed out, this isn't exactly a warm bias, it is a bias in the trend. I'd prefer a "warming" bias to a "warm" bias and will use that expression.

Argument 1 in favor of a warming bias is that, lacking one,
there should not be an increasing divergence with time between the tropospheric and surface temperature anomalies [Karl et al., 2006]. The difference between lower troposphere and surface anomalies should not be greater over land areas.
Well, the first part is half-sensible. One needs also to eliminate the possibilities that 1) the measurements are real 2) the measurements are sufficiently noisy as to be indeterminate or 3) there is a cooling bias in the sondes and satellite records.

Argument 2 is that in the absence of a warming bias
the divergence should not be larger for both maximum and minimum temperatures at high latitude land locations in the winter.
One wonders if any meteorologists were involved at all. It's hard to fathom the word "divergence" being used in this way, but presumably this refers to the increasing difference between surface and troposphere estimates. Even with that said, I am having trouble parsing the claim. Are they saying the divergence is larger in winter than in summer? Are they claiming that this largerness supports a warming bias at the surface?
Our findings suggest that the supposed reconciliation of differences between surface and satellite datasets [Karl et al., 2006] has not occurred.
Did Karl et al make such a claim? It seems a bit of a straw man. It seems like Karl et al bent over backwards to leave room for Christy's position. Anyway after a fairly random pitch for UAH over RSS data, they separate surface points into land and sea points, and assert
Table 1 also clearly shows that there has been enhanced warming over land areas when compared with ocean areas, especially in the surface temperature datasets. For example, the NCDC dataset indicates nearly three times as much warming over land areas as over ocean areas during the past thirty years. Over this same time period, the UAH lower troposphere temperature estimate indicates about half as much warming over land areas, which is contradictory to the expected global surface/lower troposphere amplification

...

Table 1 also clearly shows that there has been enhanced warming over land areas when compared with ocean areas, especially in the surface temperature datasets. For example, the NCDC dataset indicates nearly three times as much warming over land areas as over ocean areas during the past thirty years. Over this same time period, the UAH lower troposphere temperature estimate indicates about half as much warming over land areas, which is contradictory to the expected global surface/lower troposphere amplification. However... there is a documented spurious warm shift in RSS data around 1992 that is the source of virtually all of the difference between the two satellite datasets. Thus, the closer agreement of RSS with the surface temperature datasets is likely largely due to this spurious jump.

Erased from d'Aleo's version of figure 1 is "the trend difference that would be expected given the 1.2 amplification factor expected from the models." Looking at the figure, we see that they are claiming that a surface temperature increase of dT should imply a tropospheric increase of 1.2 dT. 1.2 appears to be the global mean factor backed out of global models from Santer et al '05. It seems necessary to determine whether that paper separated out land and sea points. It's not clear why a global average ratio should apply over the much more rapidly warming non-maritime regions. Wouldn't the global troposphere be much more affected by maritime conditions than would the land surface?
The warm bias in the temperature data would most likely be in evidence over land areas where larger vertical temperature stratification occurs near the ground along with a reduction of the atmospheric cooling rate. This effect will be largest in the higher latitudes, especially in minimum temperatures during the winter months, since any reduction in the cooling rate of the of the atmosphere will result in a particularly large temperature increase near the ground surface in this strongly stably stratified boundary layer.
OK, again we mean a warming bias not a warm bias. But what does the rest of that claim mean?

I'm taking a break at this point.

Can anyone tell us what that bit (lines 319-324) means? If they are looking for a bias in the instrumental record, why are they making a dynamical argument?

5 comments:

thingsbreak said...

I've only just started reading, but at first glance it looks like they're attempting at least three gambits:

- assert the accuracy of the sat record over the instrumental, and the primacy of the UAH record in particular
- assert that one or more of the alleged "fingerprints" of enhanced greenhouse warming (increased nighttime (also wintertime?) temps) can be (at least partially) accounted for by UHI
- attempt to gray wash (did I just coin that? doubtful) Watts' surfacestations pet project

As I'm sure you know, Pielke Sr. is a longtime backer of the "underestimated/unaccounted for UHI influence" claim. Senior has also been head over heels for Watts, especially of late. Christy's interest in promoting the UAH sat record is self-evident. The overall effect of the paper is to diminish the amount of warming that we've already "had", which will in turn be used to argue for lower warming to come, and thus ultimately against mitigation.

Michael Tobis said...

This certainly is the way they want the paper to be taken, but it doesn't make a case that you'd bet the planet on; ultimately it is about the tropospheric middle troposphere and the land surface under it.

Even if their speculation makes sense they are trying to make it carry a huge burden.

But if they are going to build the whole case for delay around the tropical troposphere, it might make sense to understand what, if anything they are saying. I'm stopped at a point where I don't quite get what they are saying and trying to decide if it makes much sense.

I am not expert in observations or aobservational statistics, so I am also trying to provide a realistic model of someone plowing through a paper in a tangentially related field.

Scientists always try to pretend their understanding of what each other have written is easy. Consequently the good ones stay on safe turf and the bad ones just mess up constantly. It's a bad habit. I have little enough to lose that you can see my confusion spread out before you.

Steve Bloom said...

Just to clarify, things, RP Sr. very much was the inspiration for the Watts project, so the proprietary rhetoric is no coincidence.

Steve Bloom said...

Also, this work by Arthur Smith from a few months back may be helpful.

thingsbreak said...

@MT:

if they are going to build the whole case for delay around the tropical troposphere

Lindzen, Christy, Spencer, Michaels, Singer, Douglass et al. have been banging that drum relentlessly. I suppose it was only a matter of time before the Pielkes joined in.

I think that the proper perspective from which to read this paper is this:

1). There are ostensible discrepancies* between certain observations relating to the tropical troposphere and anthropogenic warming.
2). Denialists of all stripes have seized upon this- from the out and out loons to the "serious" ones that still try to maintain a veneer of professional respectability.
3). The McLean, de Freitas, Carter paper was not unique in saying one thing and being ludicrously touted by its authors as saying another. Douglass et al. 2007 was similarly flogged by its authors as "disproving" anthropogenic warming (e.g. here).
4). Santer et al. 2008 received such attention from the denialosphere (even warranting an attack at CA) precisely because it attempted to put the issue to bed. This paper can be seen as yet another attack on Santer et al. 2008, and on the RSS record as well (used by the Santer paper).

*However the data regarding tropical tropospheric trends are unclear, as the ostensible discrepancies may be artifacts rather than "real" obs (e.g. Allen & Sherwood 2008).

@SB:

Just to clarify, things, RP Sr. very much was the inspiration for the Watts project, so the proprietary rhetoric is no coincidence.

I'd completely forgotten that.