The State of Global Warming Science
So given all the above uncertainties, the approach that Mann, Briffa, the CRU and the IPCC have taken is to ignore all this and try to reconstruct temperature trends and correlate them with CO2 to make predictions in the future.
To do this, you need accurate temperatures going as far back in the past as you can get, and you need accurate measures of CO2 going back in the past as well. But this is a very hard thing to do, and all the current approaches have serious limitations.
For example, one of Mann’s chief data sources for his historical temperature reconstruction are tree ring cores - trees grow at different rates based on temperature. So all else being equal, by measuring the rings of a tree that lived for hundreds of years, you can get an idea of how temperature increased or decreased in that time. The key here, though, is ‘all else being equal’. A year of drought can affect growth. So can a flood, or an insect infestation, or unusual cloud cover, or all sorts of things - some of which aren’t even understood. So, selecting just the right set of trees becomes important - and a source of bias.
In this particular case, Mann settled on a set of 12 cores selected by Keith Briffa, called the “Yamal Series”. There has been plenty of criticism of this. For one thing, 12 cores is an awfully small sample size. For another, some scientists have wondered what was so special about those 12 trees - many other cores in the same region were also taken. And it turns out, if you take any subset other than those specific 12, you get a very different temperature result. Either by accident or intention, these 12 seem to be almost cherry-picked to get the result needed to make Mann’s theory work.
In addition, Briffa’s trees stopped responding accurately to temperature in 1960 - and no one knows why. Mann’s answer was to ‘hide the decline’ by splicing actual measured temperatures onto the same line for the after-1960 period. This is bad science. It’s misleading. And it ignores the point that if the trees were responding differently after 1960, and we don’t know why, how do we know that they didn’t respond differently in the past? What Mann did would be somewhat akin to an astronomer deciding the ‘science is settled’ around the orbital motion of planets - except for that pesky Mercury, which seems to be anomalous. So, just splice in the ‘known’ orbit information in place of the ‘unusable’ orbital data of Mercury, and now everything works! Yay!
Anyway, temperatures in one region are not a good proxy for global temperature. It can be hotter than usual in one place, and colder than usual in another. One of the criticisms of Mann is that his ‘hockey stick’ graph does not show a Medieval Warming Period and Little Ice Age. These were fairly well established features in science until Mann’s Hockey Stick came along. The CRU E-mails suggest that he ‘smoothed’ them away by using statistical methods - a somewhat dubious practice, especially since he seemed to admit that he repeatedly tried different techniques until he managed to eliminate them (with the MWP and LIA in place, the current temperatures don’t look very abnormal).
Now, global warming scientists say that in fact they didn’t exist at all, and were artifacts of having only certain local measurements. That’s awfully convenient for Mann, who removed them before such evidence existed. Or perhaps the current evidence is also cherry-picked. There are plenty of scientists who still believe they existed.
Where you get to is that once you get past the basic chemistry of warming, it gets a lot fuzzier. There are plenty of papers still being published which call into question some of the foundations of AGW theory. It is by no means ‘settled science’ when we start talking about long-term effects, and the statistical and modeling techniques used to sidestep the complexity of earth’s interactions and use past data to model the future all have various flaws or concerns. And despite the claims of AGW proponents that there are many temperature reconstructions, and they all generally agree, the fact is that they are all intertwined in some way, either using the same raw data or building on each other’s results, and that most of the scientists working on this stuff stay in close communication. Normally, I’d say that’s not a problem, but the CRU E-mails have shown that many of these people behave in decidedly unscientific ways, and have colluded to do things like block papers from being published, stall peer reviews to keep inconvenient papers on the sidelines as long as possible, punish editors who dare to publish papers they don’t agree with, peer review each other’s work, unethically pass review material to each other breaking rules of anonymity and conflict of interest, etc. I have no faith that some of these people are acting as responsible scientists. They are advocates of a political cause, and they behave like it.
If you get away from the hysteria and the headlines that are trumpeted each time a paper is published that makes AGW look worse (as opposed to the silence or open hostility that greets papers which make it seem more questionable), you find that the actual scientific consensus is much more modest than the alarmists would have you believe. The ‘best estimate’ from the IPCC is on the order of 3 degrees of warming over the next hundred years, with sea level rises of perhaps a third of a meter. The error bars around this estimate are very large - ranging from no real warming at all other than what’s expected of the interglacial period, to warming of about 6-7 degrees. That the range is so large tells you just how unsettled the science really is. There is still much we don’t know.
