So I looked at the graphs. They are Hansen and colleagues' graphs of average temperatures for the United States in reports they produced in 1999 and 2001. They include adjustments for the fact that stations near urban areas may be influenced by changing local environment. The 1999 chart uses information about the size of the nearby community and comparisons to the behaviour of the nearest rural stations to apply the adjustment. The 2001 chart uses the intensity of nighttime lighting as measured by satellite to determine whether an adjustment may be necessary. It also incorporates two other significant adjustments to the data: a correction for the systematic effects of changes in time of observation that occured at many of the stations, and adjustments for station history (e.g., location and other changes during the recording period). The link you provided is to a blogger who is having trouble accepting how these adjustments play out in the two graphs.

The fact that the charts do not show higher recent temperatures than in the 1930s for the USA is discussed in the 1999 paper. Hansen et al include a brief discussion of possible mechanisms, including aerosol effect. They caution against putting too much emphasis on aerosols playing a dominant role in this. Apparently the distribution of sea surface temperatures alone is enough to cause a decline in US temperatures of the magnitude observed over that period, without considering radiative forcings. They also point out that the averaging of the US temperatures in those charts masks large geographic variation within the US, ranging from a warming trend in the west to cooling in the southeast. They also point out that the US constitutes 2% of the global surface. The major finding of their 1999 paper, the global change in temperature, is found in Figure 4 on page 36 of this ~16Mb pdf.
Similar results have been found by other groups investigating the topic. Citations are in the aforementioned pdf, if you care to read it.

The following links are to pages from the US Congress-commissioned report "Surface Temperature Reconstructions for the Last 2,000 Years", published last year. It "assesses the state of scientific efforts to reconstruct surface temperature records for Earth during approximately the last 2,000 years and the implications of these efforts for our understanding of global climate change.. Each page features relevant chart.

The Instrumental Record.

Note, this is not Hansen et al's work.


Documentary and Historical Evidence

Of course, given the nature of the observations, the error bars are quite wide.


Tree Rings

I really don't understand the intricacies of using dendrochronology to assess temperatures, but tree ring growth integrates a lot of factors. I don't know how they get the temperature signal out of it.


Marine, Lake, and Cave Proxies

There are many charts included in this chapter of the book. I've only linked to the first page. I haven't the time to digest everything they're saying in there.

Ice Isotopes

Not a lot of cores in that aggregated record.


Glacier Length and Mass Balance Records


Boreholes



The report discusses large-scale proxy reconstruction techniques, and includes the criticisms by McIntyre of Mann's work.


In their summary, they include this selection of reconstructions by six different teams.

There is a lot of text there, but here is their conclusion re Mann et al's original work:

"The basic conclusion of Mann et al. (1998, 1999) was that the late 20th century warmth in the Northern Hemisphere was unprecedented during at least the last 1,000 years. This conclusion has subsequently been supported by an array of evidence that includes both additional large-scale surface temperature reconstructions and pronounced changes in a variety of local proxy indicators, such as melting on ice caps and the retreat of glaciers around the world, which in many cases appear to be unprecedented during at least the last 2,000 years. Not all individual proxy records indicate that the recent warmth is unprecedented, although a larger fraction of geographically diverse sites experienced exceptional warmth during the late 20th century than during any other extended period from A.D. 900 onward."




I have not used the phrase "catastrophic climate change". The most concern I have expressed about global warming on this board is in this post, which was a direct response to the question posed in this thread. I have already commented on variation in post #69 of this thread. If a person challenges an unsupported assertion that the conclusion of a scientific paper is an "outright lie", do you think that automatically puts them in the camp of "climate hysterics"?

And getting back to Hansen's work, do you think that your choice of graphs to link accurately reflects the content of those papers?




Interesting page. I read the Loehle paper. Can't comment on his choice of proxies, robustness or lack of stastical rigour, weighting of the proxies, etc. But I find the exchanges commencing at post 143 and involving poster JEG to be informative (JEG appears to be Julien Emile-Geay who teaches a course on the "Hockey Stick) . Unfortunately. the tone is the same as what has generally kept me from even reading these debates.

I find the exercise done by RomanM in post 478 interesting. It does make one think twice about the temperatures in the centuries prior to CE 1000. If the correlation between Loehle's chosen proxies and the modern instrument record can be expected to hold true for the really old observations, then he may have demonstrated something. I imagine the same kind of excercise could be done with the proxies shown in the report I referenced above.