"THE TRICK" WASN'T SO TRICKY

The wingers have tried to make the statement below into a case of massive scientific fraud:

"I've just completed Mike's Nature trick of adding in the real temps to each series for the last 20 years (i. e. from 1981 onwards) and from 1961 for Keith's to hide the decline"

Daily Kos has an interview with Prof. Michael Mann, one of the 3 researchers Limbaugh called "frauds," and that provides links to the original papers published in the journal Nature. Here's Mann's explanation of the above quote:

The reference to "hide the decline" is referring to work that I am not directly associated with, but instead work by Keith Briffa and colleagues. The "decline" refers to a well-known decline in the response of only a certain type of tree-ring data (high-latitude tree-ring density measurements collected by Briffa and colleagues) to temperatures after about 1960. In their original article in Nature in 1998, Briffa and colleagues are very clear that the post-1960 data in their tree-ring dataset should not be used in reconstructing temperatures due to a problem known as the "divergence problem" where their tree-ring data decline in their response to warming temperatures after about 1960. "Hide" was therefore a poor word choice, since the existence of this decline, and the reason not to use the post 1960 data because of it, was not only known, but was indeed the point emphasized in the original Briffa et al Nature article. There is a summary of that article available on this NOAA site.

The Nature article Mann refers to is still online:

Reduced sensitivity of recent tree-growth to temperature at high northern latitudes

Nature 391, 678-682 (12 February 1998) | doi:10.1038/35596; Received 14 May 1997; Accepted 11 November 1997

K. R. Briffa¹, F. H. Schweingruber², P. D. Jones¹, T. J. Osborn¹, S. G. Shiyatov³ & E. A. Vaganov⁴

1. Climatic Research Unit, University of East Anglia, Norwich NR4 7TJ, UK
2. Swiss Federal Institute of Forest, Snow and Landscape Research, Zürcherstrasse 111, CH-8903, Birmensdorf, Switzerland
3. Institute of Plant and Animal Ecology, Ural Branch of the Russian Academy of Sciences, 8 Marta Street, Ekaterinburg 620219, Russia
4. Institute of Forest, Siberian Branch of the Russian Academy of Sciences, Krasnoyarsk, Russia

The abstract tells the story:

During the second half of the twentieth century, the decadal-scale trends in wood density and summer temperatures have increasingly diverged as wood density has progressively fallen. The cause of this increasing insensitivity of wood density to temperature changes is not known, but if it is not taken into account in dendroclimatic reconstructions, past temperatures could be overestimated. Moreover, the recent reduction in the response of trees to air-temperature changes would mean that estimates of future atmospheric CO2 concentrations, based on carbon-cycle models that are uniformly sensitive to high-latitude warming, could be too low.

and the main text elaborates:

Averaged around the Northern Hemisphere, early tree growth (ALL) can be seen to follow closely the decadal trends in recorded summer temperatures, tracking the rise to the relatively high levels of the 1930s and 1940s and the subsequent fall in the 1950s. However, although temperatures rose again after the mid-1960s and reached unprecedentedly high recorded levels by the late 1980s, hemispheric tree growth fell consistently after 1940, and in the late 1970s and 1980s reached levels as low as those attained in the cool 1880s. Over the hemisphere, the divergence between tree growth and mean summer temperatures began perhaps as early as the 1930s; became clearly recognisable, particularly in the north, after 1960; and has continued to increase up until the end of the common record at around 1990. The reason for this increasingly apparent and widespread phenomenon is not known but any one, or a combination, of several factors might be involved.