Focusing on the 'controversy' is a key denier strategy.
I agree with that, Paul. At the same time though, human nature being what it is, sometimes it's hard to see past our own little areas of expertise/knowledge. A poorly thought out claim from "Experts" can easily taint the whole subject for you.
For example: I don't pretend to understand the intricacies of climate models. The math involved is frankly more than just a little bit over my head and always will be. I do have a fairly decent knowledge of botany though.
Dendrochronology indicates two things about the recent past: First, atmospheric CO2 levels have risen in the last 150 years. This is typically ascertained by measurement of C12/C13 ratios at various points in the core sample. Second, mean average temperatures have also risen slightly as well. This is ascertained by measurement of radial growth and density along the sample. Increased radial growth = Longer growing season = Higher peak termperatures.
Tree-ring data indicates cooler conditions in the early 1700s, followed by warming that started about half-way through that century. An abrupt cooling occurred in the late 1700s and continued for much of the 1800s. The coldest recent period was between the 1830s and 1880s. (Officianados of American history may recall the winter of 1879-1880 as told by Laura Ingalls Wilder and others. )
A steadily increasing warming trend followed. Temperatures in the 1900s have been higher than in any other period captured by the tree rings from all over the northern hemisphere. The 10 highest growth intervals are all after 1920 and the highest 25-year growth period was between 1944 and 1968. Like all field data, this is not 100% "Clean." (Meaning there are some anomalies) There is a very tiny fertilizer effect from increased CO2 that must be factored out of growth data. Droughts like we have experienced in the American West in the 1930's, 1950's, 1980's and 2000's must also be accounted for. The end result, therefore is an amalgamation of hundreds of reconstructed chronologies, but the current consensus is that this data is reliable and accurate.
Okay. So on one hand the unnaturally good growing conditions we have experienced are actually some very good evidence that directly links rising temperature to rising CO2 levels. Trees in this century have grown much faster than in the previous century and the corresponding agricultural implication(s) at least for the Northern hemisphere should be obvious.
On the other hand, we have recent studies conducted by scientists whose primary discipline appears to be geology which blame these same conditions for the current die-back in North American forests. The only efforts I have seen to reconcile this claim with the evidence so far don't seem to be terribly plausible from the standpoint of botany. (i.e. The species in question grow in a very wide range of elevations, tempertures and precipitation levels)
Don't misunderstand. It's not that I don't realize that the growing conditions that a couple of generations have been blessed with will mean very little if the forces which likely have caused them eventually destabilize our climate. I do. It's not that I'm happy about the spread of West Nile virus here where I live. I'm not. It's just that it is all too easy not to take what is in the last analysis, a glorified weather forecast as seriously as it perhaps it should be when it appears to be marred by dubious ancillary claims.