There has been more published in the last week about the hockey stick with summaries of what it all means at Real Climate and Climate Audit.
David J commented yesterday at this blog that,
It would seem the Hockey Stick "debate" is fast going the same way as the MSU "debate".
I understand David's comment to mean that more data and analysis is confirming that current warming is 'unnatural' and a consequence of global warming from greenhouse gases.
But the following comment from Richard Lindzen (see the second reason), sent as a letter to Benny Peiser, has got me wondering confused:
Dear Benny,
The concern over the hockey stick has always struck me as weird. There are several reasons for my impression:
1. There is no doubt that Europe and the North Atlantic were warmer than they are today for several centuries during the high middle ages. This is more than enough information to tell us that major climate changes can occur without the present level of industrialization -- regardless of what happened to the global mean temperature.
2. Indeed, if the global mean temperature did not change while Europe and the North Atlantic underwent very substantial warming, this would imply a major change in the geographic pattern of
temperature. However, a major assumption in the hockey stick is that the patterns remain fixed. One is then left with the paradoxical conclusion that if the hockey results are right, the hockey stick analysis is wrong.3. The medieval warm period in Europe was a period of high population, vibrant intellectual activity, and an absence of famine and plague. The onset of the little ice age was marked by famine, plague, and much reduced population. This suggests that warmth wasn't all that bad. At the same time, the Renaissance and the intellectual flowering that followed all occurred before the end of the little ice age, suggesting that human abilities can rise above the problems posed by the environment.
In many ways, the whole story can be regarded as encouraging. Yet we focus on a couple of tenths of a degree in the global mean.
Best wishes,
Dick
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Richard S Lindzen is Alfred P. Sloan Professor of Meteorology, Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology. For more information visit http://www-eaps.mit.edu/faculty/lindzen.htm .
Letter republished with permission from Benny Peiser.
Instead of relying upon computer models and proxy data why don't we first try to explain the direct data - the "what grew when and where" data from all around the world, that has never been explained as being caused by anything other than a warmer climate?
How are tools from the Medieval and Roman periods being revealed by glacial retreat in the Alps? How were tree lines higher not only in the Alps but the Sierra Nevadas? What caused the severe droughts that resulted in the demise of the Anasazi culture? How did Lake Naivasha dry up for 200 years? Why was lower England a wine-producing region (and please don't try to argue the point that now, after 900 years of breeding new varieties of grapes, and advances to growing techniques, almost all of which specifically to enhance cold-hardiness, they again grow wine grapes in lower England)? Please explain similar evidence concerning Chinese orange yields. Please explain the sea sediment records and ice core records from antartica? And of course please explain the Vikings' settlement of Greenland, and the fact that skeletal analysis shows that their diet was 80% land-based until the 1300s when it suddenly turned to 80% sea-based, before their settlement died out?
Before the climate became a political issue, the universally accepted climate history included a warmer MWP. This was based largely upon the direct evidence of what grew when and where - events that, since they occurred have been interpreted to mean a warmer climate. Not a single example has been explained as having happened for any other reason.
It's a bit like saying that based upon a reconstruction, it's impossible for Washington to have crossed the Delaware with his men, without explaining how it is that they managed to end up on the other side.
The only alternative would be to show that somehow, in the remaining parts of the world from which there is no evidence either way - parts that, I may add, are not contiguous - there was an equal and opposite cold spell that offset the MWP where the evidence exists. This would of course require that the climate worked differently than it works now, which would also have to be explained.
Ian Castles and William Connelley had a discussion about what I said and did not say. Here is my version.
If one assumes convergence of per capita income, and one measures income in purchasing power parity (PPP) exchange rates, then projections of global carbon dioxide emissions are lower than in case one measures income in market exchange rates (MER).
This is the original Castles and Henderson critique of IPCC SRES.
However, emission intensities are also assumed to converge, which partly offsets the above effect.
This was pointed out by Manne and Richels, and by Alfsen and Holtsmark, while Castles and Henderson admitted their initial omission.
As a result, switching from MER to PPP reduces global carbon dioxide emissions, but by an amount that is small compared to the uncertainty about future emissions.
That is, if one is interested in long-term, global climate change, the Castles and Henderson critique is of minor importance.
However, one should worry about the fact that the IPCC, first, made a very basic error and, second, is unable to admit that and correct its way.
If one is interested in climate policy, the Castles and Henderson critique does matter, because the small drop in global emissions is almost entirely due to China and India. The OECD thus shoulders a larger part of the responsibility. The argument of the US Senate, that climate policy without China makes no sense, cuts less wood.
If one is interested in climate impacts, the Castles and Henderson critique does matter, because projected economic growth is slower in developing countries, and vulnerability is larger as a result. Although warming would be slower, impacts may in fact be larger.
If one is interested in regional climate change, the Castles and Henderson critique does matter, because future emissions of sulphur would be different as well, probably higher.
In sum, Castles and Henderson raise five issues, only one of which is of minor importance.
By the way, my reading of the state-of-the-art in economics is that (a) income should be measured in PPP nor MER; (b) there is neither theoretical nor empirical support for the assumption of unconditional income convergence; (c) there is limited empirical support for the assumption on energy intensity convergence.
Richard Tol