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 analysesAs 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 amplificationErased 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?
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.
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?