Archive for the ‘Temperature History’ Category.
Loehle, Via Climate Audit (temperature anomaly over last 2000 years or so, via proxies):
If your are interested in temperature proxies, check out the CA post. It has what I have never seen before, a gallery of graphs of all the individual proxies that go into the summary/average above. Lots of noise is my chief observation.
To some extent, 1000-year temperature histories are moderately irrelevent to modern global warming discussions. In fact, it is fairly amazing that the evidence of tree rings and such over 1000 years is discussed more than the instrumental record of the last 100, which tends to undercut most catastrophic warming forecasts. However, catastrophists have attempted to use these past temperature reconstructions to make the argument that temperatures were incredibly stable and low right up to the point that man has made them higher and less stable in the last 100 years. For this reason it is worth discussing them, if only to refute this conclusion.
I won’t go into a lengthy discussion of historical reconstructions, as I alread have in my book and in my movie (both free online). In this post I just want to talk about one issue: the splice.
Below is the 1000-year temperature reconstruction (from proxies like tree rings and ice cores) in the Fourth IPCC Assessment. It shows the results of twelve different studies, one of which is the Mann study famously named "the hockey stick."
Among many issues, I pointed out the fact that this chart appends or splices the black line, actual measured temepratures, onto the colored lines, which are the historical temperature reconstructions from proxies.
I made the point that this offended by scientific training: When one gets an inflection point right at the place where two data sources are spliced, as is the case here, one should be suspicious that maybe the inflection is an artifact of mismatches in the data sources, and not representative of a natural phenomenon. And, in fact, when one removes the black line from measured temperatures and looks at only proxies, the hockey stick shape goes away:
The other day I discovered that this inflection point is a fairly old criticism (no surprise, I never claim to be original). Old enough, in fact, that Michael Mann and the folks at realclimate.org have fired back:
No researchers in this field have ever, to our knowledge, "grafted the thermometer record onto" any reconstruction. It is somewhat disappointing to find this specious claim (which we usually find originating from industry-funded climate disinformation websites) appearing in this forum.
The guys at realclimate are just so cute with the "industry-funded climate disinformation" attack — they remind me of the Soviets and how they used to blame everything on CIA plots. I can say that 1) I recognized this problem on my very own after about 20 seconds of looking at the graph and 2) I have yet to recieve my check from the industry cabal.
It turns out, however, that this is wildly disingenuous. What they mean is that none of the colored lines include gauge measures grafted onto older proxy data. But I never really accused them of that. Interestingly, Steve McIntyre argues that even this claim is wrong, and some of the colored lines do include spliced-on gauge measures.
But my point, which Mann has never refuted or addressed, is that whether the proxy lines themselves include grafted data or not, the proxy lines are NEVER shown to the public or to policy makers without the gauge temperature line added to the chart. Have you ever seen the proxy lines as they are in my third chart above without the 20th century gauge temperature line? If in policy discussions and media reports, this gauge temperature line is always included on the graphs in a way that it looks like an extention of the proxy series, then effectively they are grafting the data sets together in every discussion that really matters.
By the way, it is fairly easy to demonstrate that the proxy studies and the gauge temperature measurements do not represent consistent and therefore mergeable data sets. Over hundreds of years, we have developped a lot of confidence that the linear thermal expansion of mercury in a glass tube is a good proxy for temperatures. We have not, however, developped similar confidence in bristle cone pine tree rings, whose thickness can be influenced by everything from soil and atmospheric composition to precipitation. Lets look at a closeup of the graph above:
You can see that almost all of the proxy data we have in the 20th century is actually undershooting gauge temperature measurements. Scientists call this problem divergence, but even this is self-serving. It implies that the proxies have accurately tracked temperatures but are suddenly diverting for some reason this century. What is in fact happening are two effects:
All of this just confirms that we cannot trust any conclusions we draw from grafting these two data sets together.
By the way, here is a little lesson about the integrity of climate science. See that light blue line? Here, let’s highlight it:
For some reason, the study’s author cut the data off around 1950. Is that where his proxy ended? No, in fact he had decades of proxy data left. However, his proxy data turned sharply downwards in 1950. Since this did not tell the story he wanted to tell, he hid the offending data by cutting off the line, choosing to conceal the problem rather than have an open scientific discussion about it.
The study’s author? Keith Briffa, who the IPCC named to lead this section of their Fourth Assessment.
More discussion on this topic can be found in my book and in my movie (both free online).
Many of you have probably read about the disputes over temeprature histories like Mann’s hockey stick chart. I thought you might be interested in how some of these 1000-year long proxies are generated. There are several different approaches, but one that Mann relied a great deal on is measuring tree rings in bristle cone pine trees. Here is a picture of a researcher taking a core from a very old tree that is then sent to a lab to have it’s ring widths measured.
In theory, these ring widths are directly proportional to annual temepratures, but there are a lot of questions about whether this is really true. Other factors, like changing precipitation patterns, might also affect ring widths, and there may be reasons why the scale could change over time. Remember, we only have a few decades, at most, of good temperature data to scale growth in a tree that goes back over a thousand years. In fact, scientists are finding that, more recently, tree ring proxy data for current growth is diverging from surface temperature data, meaning either that surface temperature data is flawed or that they don’t really understand how to scale tree ring data yet. Interestingly, and as a sign of the health of climate science, researchers have reacted to this problem by … not updating tree ring proxy databases for recent years. That’s one way to handle data that threatens your hypothesis — just refuse to collect it. Much more on proxy histories here.
On this blog and at Coyote Blog, we have focused a lot of attention on the adjustment processes used by NOAA and James Hansen of NASA’s GISS to "correct" historical temperatures. Steve McIntyre has unearthed what looks like a simply absurd example of the lenghts Hansen and the GISS will go to tease a warming signal out of data that does not contain it.
The white line is the measured temperatures in Wellington, New Zealand before Hansen’s team got hold of the data. The red is the data that is used in the world-wide global warming numbers after Hansen had finished adjusting it. The original flat to downward trend is entirely consistent with sattelite temeprature measurement that shows the southern hemisphere not to be warming very much or at all.
What do these adjustments imply? Well, Hansen has clearly reduced temperatures down in the forties while keeping them about the same in 1980. Why? Well, the only possible reason would be if there was some kind of warming bias in 1940 in Wellington that did not exist in 1980. It implies that things like urban effects, heat retention by asphalt, and heat sources like cars and air conditioners were all more prevelent in 1940 New Zealand than in 1980. However, unless Wellington has gone through some back to nature movement I have not heard about, this is absurd. Nearly without exception, if measurement points experience changing biases in our modern world, it is upwards over time with urbanization, not downwards as implied in this chart.
Postscript: A perceptive reader might ask whether Hansen perhaps has specific information about this measurement point. Maybe its siting has improved over time? However, Hansen has to date absolutely rejected the effort made by folks like surfacestations.org to document specific biases in measurement sites via individual site surveys. Hansen is in fact proud that he makes his adjustments knowing nothing about the sites in question, but only using statistical methods (of very dubious quality) to correct using other local measurement sites.
Last week we saw how Antarctic ice is advancing, but somehow this never makes the news despite huge coverage of Arctic ice retreats.
One good reason for this may well be that there has been no measured warming in Antarctica over the last 50 years.
Steve McIntyre summarizes
As I’ve discussed elsewhere (and readers have observed), IPCC AR4 has some glossy figures showing the wonders of GCMs for 6 continents, which sounds impressive until you wonder – well, wait a minute, isn’t Antarctica a continent too? And, given the theory of “polar amplification”, it should really be the first place that one looks for confirmation that the GCMs are doing a good job. Unfortunately IPCC AR4 didn’t include Antarctica in their graphics. I’m sure that it was only because they only had 2000 or so pages available to them and there wasn’t enough space for this information.
