Just for clarity, the influential Rahmstorf 2007 paper that is contradicted by published evidence here, was irrevocably discredited by his own admission here, that apparent increased climate sensitivity was only due to ‘weather’.
In hindsight, the averaging period of 11 years that we used in the 2007 Science paper was too short to determine a robust climate trend. The 2-sigma error of an 11-year trend is about +/- 0.2 ÂºC, i.e. as large as the trend itself. Therefore, an 11-year trend is still strongly affected by interannual variability (i.e. weather).
Its not discredited by the smoothing method necessarily, that involves padding the data series, although padding data series is problematic in a number of ways.
Questions about the validity of the smoothing in Rahmstorf et al 2007 (see CA here for a belly-laugh) invariably turn into questions about how to smooth in general. With so many ways to do it, what is the right or best way?
One aspect of the question is illustrated in the figure below, which is a replication of Rahmstorf 2007 done a few different ways. The blue lines, are the trends using singular spectrum analysis (SSA) with embedding periods of m=11 (dashed) and m=14 (solid) respectively, and the minimum roughness criterion (MRC). Embedding period makes some difference. The red lines, however, are the result of applying ssa without MRC. This makes a bigger difference. (The smooths are translated for readability).
The MRC is achieved by padding the end of the data series with a line of slope, equal to the slope of the last m points. The red lines above are SSA but not padded. Now padding with points could be done in a number of ways, and the article by Mann 2004 lays out the rationale for these paddings. Padding may even be ‘implicit’ when there is no padding. But the idea of padding the ends of the data series raises questions in most peoples minds. For example, here is a quote from an article in American Thinker.
Most damning, Harvard meteorologists have been unable to replicate the findings of the UN’s International Panel on Climate Change (IPCC) without the use of a technique called “data-padding.” The IPCC actually admitted to engaging in this deceptive practice. Without this padding, the infamous warming trend falls by several degrees. In essence, the IPCC and its primary source manipulated data (dare we say “lied”?) to produce a desired result.
Rightly or wrongly, padding is synonymous with fabrication in most peoples eyes. The padded data on the graphs above can be seen as the straight lines on the right hand end. Adding this data, can be seen as an expression of an expectation that the data will continue to increase along the lines that it has in the recent m points. Although, the recent down-turn lead to a modification of the parameters in the same graph in the Copenhagen Synthesis Report to increase the m points, so the temperature trend continued to go up. So it can be seen that the implicit expectation is not so much that trends will continue, but the expectation that temperatures will go up. So why not just pad the data series with a line where you ‘think’ the temperature is going to go? It would be the same thing.
In another American Thinker article Journalists protest Global Warming spin cycle, according to the Columbia Journalism Review, the NSF’s (National Science Foundation) Jeff Nesbit was met with “consternation” at the London conference for “attempting to ‘disguise’ publicity as objective reporting.” Apparently, the NSF is so heavily invested in propagating the Global Warming party line by producing content for news outlets, journalists are revolting.
Global warming researchers are sometimes accused of chasing research dollars with alarmist rhetoric. The NSF also requests a budget increase of doubling of funding for “basic research” over the next decade.
The bottom line of the article is a warning of the dangers of mis-using science as a crutch to prop up political ambitions. The problem with padding the end of the data series, is that it can easily be seen a a crutch to prop up the faltering temperature trend.
 Willie H. Soon, David R. Legates, and Sallie L. Baliunas, “Estimation and representation of long-term (>40 year) trends of Northern-Hemisphere-gridded surface temperature: A note of caution,” Geophysical Research Letters, vol. 31, 14 February 2004, 2.