As a follow on to my previous two posts is this piece about the reconstruction of global temperatures over the past 2,000 years. (Well, actually 1,995 years, but who's quibbling?)
This latest reconstruction used a host of proxies from all over the world, but excluded tree-ring proxies - something used by a number of climate researchers, including Mann – because of their unreliability.
...Loehle notes that many long-term reconstructions of climate are based on tree rings, but “There are reasons to believe that tree ring data may not capture long-term climate changes (100+ years) because tree size, root/shoot ratio, genetic adaptation to climate, and forest density can all shift in response to prolonged climate changes, among other reasons.” Furthermore, Loehle notes “Most seriously, typical reconstructions assume that tree ring width responds linearly to temperature, but trees can respond in an inverse parabolic manner to temperature, with ring width rising with temperature to some optimal level, and then decreasing with further temperature increases.” Other problems include tree responses to precipitation changes, variations in atmospheric pollution levels, diseases, pest outbreaks, and the obvious problem of enrichment that comes along with ever higher levels of atmospheric carbon dioxide. Trees are not simple thermometers!Instead, Loehle used such things as “borehole temperature measurements, pollen remains, Mg/Ca ratios, oxygen isotope data from deep cores or from stalagmites, diatoms deposited on lake bottoms, reconstructed sea surface temperatures, and so on.” Loehle's reconstruction used everything except tree-ring data.
His results show both the Roman and Medieval Warm Periods as well as the Little Ice Age, which Mann's did not. Loehle's results also mirrored those of Svensmark, who used Carbon-14 data to determine solar activity over the past 1,000 years. Others have taken that even farther, going back almost 3,500 years. Loehle's global temperature chart mirrored that of the solar activity plotted by Svensmark and others, giving us further clues into another driving force behind climate change.
Could this be another bit of ammunition to use against the Global-Warming-Is-All-The-Fault-Of-The-Evil-Humans theory of climate change? Maybe.
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One of the most bothersome things I've noticed about those supporting AGW as fact is their constant citing of CO2 data as the only thing we need to concentrate on. They seem to think that 'heat trapping' by atmospheric CO2 is a linear relationship, meaning as the concentration of CO2 increase, it's heat trapping increases likewise. But it doesn't. More than a few studies show that after it reaches a critical concentration, further increases have little effect on heat trapping. We're already past that point, meaning the CO2 effects have reached saturation.The AGW faithful also ignore such things as solar activity, claiming it's variations to be so small as to be meaningless. But they overlook or ignore other effects variations in solar activity can have that has nothing to do with its radiance. Certainly Svensmark's work implies they are discounting a very big factor that affects Earth's climate. (It certainly seems to affect surface and atmospheric temperatures on Mars, the Jovian and Saturnian moons, and Pluto!)
This topic will continue to generate a lot of commentary. I won't say it will create a lot of debate because you cannot debate with true believers, particularly with those of the AGW faith.
And so it goes.