Is global warming regional - as in the MWP?

I was looking over Anthony Watts’ web site, and noted a picture that he had posted that shows the large number of stations around the United States that were showing record temperatures.

Places in the United States showing record temperatures (From WUWT)

What struck me was that, just as one could argue that this showed how cold we were getting, those that argue that carbon dioxide is raising global temperatures could as easily point to the points in the Western part of the country as evidence for their argument.

The problem of trying to determine which arguments are more accurate is made more difficult where there is this isolation of data, so that those seeking information are only presented with that which supports one side – so cheers to Anthony for showing both.

But individual data points, while interesting, don’t really reflect the sort of long-term changes that are predicted (or not) by various climate models. There is a considerable question over the accuracy and methodology used to derive an average measure of the global temperature, with satellite data, which was supposed to be more accurate, having its own limitations, in measuring ocean temperatures for example.


If one looks at the average temperature for the contiguous United States, for example,

Average US temperatures since 1880 (GISS )

One can see that the average for the country has been tending downwards over the last decade, and has not differed that much from the temperatures of the 1930’s (which still has the record for the hottest year). It is hard to argue for AGW based on this graph alone.

Yet if once compares the data from the two hemispheres, it is the Northern Hemisphere that is warming much faster than the Southern.

Hemispheric temp changes (GISS)

So if the US landmass isn’t warming, and the Southern Hemisphere isn’t currently doing much either where is all the global warming coming from? A look at the current temperature anomalies shows that it is the Arctic and Europe that is warming the most:

Global temperature anomalies (GISS)

But it is interesting that the actual anomaly is only 0.54 degrees, since, as I have noted before, the predictive values that Dr Hansen gave in the paper that is the most cited as authoritative on this predicted that by now the temperature would be between 1.0 and 1.2 degrees higher than the datum, and that only if there was dramatic reduction in greenhouse gases would we get to 0.65 degrees by now.

Now that is still a it higher than the 0.42 degrees – which Anthony is reporting and which is, I presume, the daily difference, but as he notes, the carbon dioxide levels are at 388 ppm, and if the impact was a severe as has been modeled it should be much higher (though the GISS graph above does show that it is heading backup).

But the other thing to comment on is that back when those of us who bring up the Medieval Warming Period (MWP) first did so, the response of the AGW proponents was that we were discussing something that was only true of Europe and the Arctic. Now that we are seeing a pattern that shows a regionalization of the global warming pattern I wonder if that argument can’t be reversed?

It is only by openly discussing these changes and their implications that true scientific understanding can be achieved, not by hiding, or adjusting data in less than transparent ways. Unfortunately scientific debate takes time and evidence only accumulates slowly. How long, for example must the current apparent cooling persist, (or the accelerated increase in temperature not occur) before the model predictions are discredited? Yet without that debate we risk the frittering away of resources on valueless measures that will have no impact on the future.