Talk:List of climate change controversies/here

Hockey Stick

Obviously the hockey stick controversy needs to be described in the article.

The hockey stick study by Mann came after the Kyoto protocol was written up, so the original motivation for Kyoto was not based on this.
The hockey stick graph was used by Kyoto activists to drum up support for the climate treaty.
The graph was prominently highlighted by the IPCC TAR, and the U.S. NAS found this to be inappropriate, given its graph's recent (at the time) and flawed nature.
There were flaws in the statistics of the Mann reconstruction, as found by McIntrick & McIntyre, as well as the NAS and others.
These flaws did not significantly alter the results. Fixing the problem with the statistical method yields essentially the same graph. Using all of the data yields the same graph. Using different methods yields the same graph. Multiple studies by different scientists yield the same graph. (Same="substantially similar" as I use it here, for brevity)
There are difficulties using proxies, but it is possible to quantify this uncertainty, as must be done with essentially all indirect observation of the past.
There were also flaws in the McIntrick & McIntyre paper, as found by several subsequent peer-reviewed publications.
It is generally accepted that there was a medieval warming period. The question at hand is whether it was or was not warmer than present.
Even the latest assessment report gives a confidence of only "likely" that the present is warmer than the MWP. This is an acknowledgement of the uncertainties inherent in our ability to reconstruct past temperatures.
Opponents of global warming theory widely proclaimed that the "hockey stick is broken", and that the theory of global warming must be wrong as a result.
The theory of anthropogenic global warming does not depend on this graph or any other historical temperature reconstruction, but upon analysis of direct measurements taken in the 20th century. Historical trends provide context for, and not proof of, what we observe today.
The Wegman report was also critical of the error's in Mann's reconstruction, and highlighted the need to involve statisticians in these reconstructions, but did not address their signficance - i.e. that fixing the errors does not significantly change the results.
Today's scientific opinion is that the basic shape of the hockey stick is correct, though we cannot be certain enough of past temperatures to conclude that we are definitely warmer now than during the MWP.
Present temperatures are rising more rapidly than during the MWP, and accelerating rather than tapering off to a peak, leading scientists to project that temperature levels last seen in the MWP will be exceeded in the 21st century if we have not exceeded them already. Committed change is estimated at 0.6C, and rate of change expected in the early part of this century is 0.2C per decade.

Errors in the above

It says:

These flaws did not significantly alter the results. Fixing the problem with the statistical method yields essentially the same graph. Using all of the data yields the same graph. Using different methods yields the same graph. Multiple studies by different scientists yield the same graph. (Same="substantially similar" as I use it here, for brevity)

This is not accurate. McKitrick published a reconstruction after removing Mann's errors and 20th century temperatures were seen to be unexceptional. See Figure 8 on page 14. [1] You are correct to say Mann admitted his errors. He published a Corrigendum. However, if you say none of Mann's errors mattered - then you are taking Mann's side in the debate and the statement is contrary to the facts. Mann denied the claim of McIntyre and McKitrick that his approach would produce a Hockey Stick from red noise. However, others confirmed that M+M were correct. This error must be corrected. RonCram 22:45, 21 February 2007 (UTC)[reply]