Nowhere in the actual paper does it say "global warming is significantly overstated."
...also from the paper:
p.17 ...fyi: (OMR = "observation-minus-reanalysis" (p.14))
Key results found by Lim et al. [2005, 2007] are:
Surface temperature anomalies averaged over the Northern Hemisphere (NH) derived from three reanalyses (ERA40, NNR, and NNR II (R2)) and two observations show a gradual warming trend both for reanalyses and observations (Figure 17). It is also evident that the observations exhibit a larger warming trend compared to reanalyses (Figure 17a). As a result, OMRs show a positive trend (Figure 17b), with a larger trend using NNR or R2 than ERA40.
I read this paper and (being familiar with Pielke's work) I recognized that about 90% of this paper is composed of previous Pielke papers, on SAT (Surface Air Temp.) inaccuracies. So, he finally got all that work published in a peer-reviewed journal!
The other 10%, where he decries the formula used by the NRC, also advocates using other observations (ocean heat content) for determining temperature trends. So, in summary, the formula is also inadequate, in addition to the T' parameter being inaccurate (according to Pielke).
While I agree that SAT's may be "artificially" inflated (relative to actual global temp.), that doesn't mean that they are wrong; they do reflect excess (local) heating.
Throughout the paper, trends are calculated without using SAT's. These still show definite warming trends. Look at fig.17 & 23-24 (p.17 & 22), etc.
Pielke says,
"the issues that we discuss in this paper need to be evaluated in depth;" but even if he is totally correct....
That we are experiencing today's level of climate change, with slightly less warming than we thought we had observed, should not be comforting.