The Global Warming Debate

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refill Wrote:"There is no evidence that the divergence problem is “unprecedented.” "

How can there be evidence that something is unprecedented? There can be evidence that there is precedence for something, but I don't see how there can be evidence that something is unprecedented.

It sounds like we agree on that issue. It was John Cook (Skeptical Science) who claimed that the divergence problem was unprecedented.

Quote:Can you point to a time when the "divergence problem" occurred before the last few decades? I think the SS article is saying no such data exists. Your argument seems to say since we only go back so far, we should assume that there is precedence. That does not seem prudent, when the data we do have says there is no precedence.

It was Skeptical Science that declared that the divergence in the later 20 twentieth century was unprecedented. We’re supposed to accept that statement, and thus, conclude that none of the selected proxies underestimated the earlier temperatures. Skeptical Science has the burden of proof on that detail. If we don't know whether the divergence of the later 20th century was unprecedented, then the proxies can't prove the non-existence of earlier warming.

The existence of a Medieval Warm Period (MWP) would be proof of a divergence. The existence of a MWP would also contradict unprecedented warming of the 20th century. It’s not surprising that there is significant hostility towards the idea of the MWP among many global warming advocates. David Deming, a professor of Geophysics (with specialization with temperature and heat flow) who has done some work with bore hole temperatures, was contacted by a climate researcher who told him “we have to get rid of the Medieval Warm Period.” The MWP period was generally accepted to exist until the time of the first major Hockey Stick Publication (Mann, Bradley, Hughes).

Skeptical Science has its own version of the debate about the existence of the MWP. It states the skeptic position, and then lays out what I would call a non-critical and one sided argument for his positions. Evidence supporting the skeptic side is not presented or acknowledged.

This link (The Medieval Warm Period – a global phenomenon, unprecedented warming, or unprecedented data manipulation?) gives a summary of some of the evidence supporting the existence of a MWP. Some of the evidence is historical in nature (Vikings settling in a warm Greenland, vineyards in Great Britain, etc…), some from proxy measurements, and some miscellaneous (evidence of smaller glaciers, etc…). From the global warming advocate side, this type of evidence is often dismissed along the lines of this quote from Skeptical Science:

Quote:Skeptical Science:The Medieval Warm Period was not a global phenomenon. Warmer conditions were concentrated in certain regions. Some regions were even colder than during the Little Ice Age. To claim the Medieval Warm Period was warmer than today is to narrowly focus on a few regions that showed unusual warmth

Skeptical Science concludes by stating the following and including the graph below:

Quote:What is more, and as can be seen in Figure 4, globally, temperatures during the Medieval Period were less than today.

That might be convincing if you accepted this at face value and didn’t look at opposing arguments. I’ll list a few:

The graph above is proxy reconstruction with the divergence part deleted from the later 20th century, with thermometer data spliced at the end. We still don’t know whether the earlier proxy data has any hidden divergences.

The Mann et. All 2009 paper with the graph above has many problems that are discussed here: Mann 2008: the Bristlecone Addiction

Among them are the problems with a dominant proxy (the Tiljander sediments which I mentioned in an earlier post) that rely on a nonsensical negative calibration to the sediment data. Mann also uses the flawed bristlecone pines from the western US, which the US National Academy acknowledged shouldn’t be used in temperature reconstructions.

Skeptical Science makes the claim that regional temperature trends can’t be used as evidence of global trends. However, the graph from Mann 2009 is overwhelmingly dominated by the trend from the bristlecones in the western US and a single set of sediment proxies.

As the graphic in this link shows, however, there are several proxies all over the globe which reflect warming during the Medieval period.

refill Wrote:Regarding the quality of the Skeptical Science website, it seems very well balance to me, responding to skeptical arguments on a point by point basis. If there are straw men, skeptics should identify them. The climate experts will either say why the argument is not a straw man, or concede that the point is irrelevant, or "respond" with silence.

In my opinion, the Skeptical Science is not well balanced. Skeptical Science only gives the skeptical side a brief comment, and then attacks it using one-sided arguments. An argument or rebuttal from the skeptical side is not given or even acknowledged.