Neil, Droughts are more often the result of a cold, not warm climate so if the planet warms a bit precipitation will increase rather than decrease. Of course precipitation patterns could change: some areas could get wetter and other areas could get drier. If we are in store for some climate changes, it most likely will be gradual enough so that forest ecosystems and human populations will be able to adjust without much problem.
Mike -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of neil Sent: Friday, June 05, 2009 8:40 AM To: ENTSTrees Subject: [ENTS] Re: High elevation forest response to climate change and other factors ENTS, Lee is correct in saying that there are many methods available to test for and then reduce the many factors influencing ring width. These methods have been in development for nearly a century now. And, while it is a well-established science, we are still coming up with new methods to further reconstruct environmental history. Couple quick thoughts on some of the idea in the thread here: - first, while lab studies do show an increase in plant growth when CO2 levels are immediately doubled, there is very little evidence or often contradictory evidence indicating CO2 fertilization impacts on natural trees. That isn't to say it isn't happening. It suggests either a) we do not know what we are doing yet/how to detect the influence of elevated CO2, b) the signal is so weak that it is overwhelmed by other factors, c) that only in certain growing conditions does elevated CO2 influence tree growth or d) something else is happening [i ran out of ideas here]. - people in the past have looked at global tree growth at latitudinal treeline sites, sites where global warming drives increased ring widths, removed the 'climate signal' to look for a residual increase in ring widths through time; a residual trend that might be the result of elevated CO2. that analysis revealed no trend and the authors suggested elevated CO2 was not an important factor of tree growth at these sites [but, this result could come back to a) above] - there is an incredible network of tree ring records 700 to 1000+ yrs in length in the western US, including Henri's 2000 yr record from New Mexico. An investigation looking at the percent of annual drought in this region does indeed suggest that the recent drought is becoming more severe than most droughts of the last 600 yrs. however, this same record indicates that the region was quite dry from 900-1300 A.D. If a similar drought hit today, well civilization would be altered significantly. you can find the abstract of this paper here: http://www.sciencemag.org/cgi/content/abstract/306/5698/1015 the data set from which this analysis is derived from is publicly available here: http://www.ncdc.noaa.gov/paleo/pdsi.html in fact, an update of this data set, V2, is available here. You can make maps of drought from this data set, too. neil --~--~---------~--~----~------------~-------~--~----~ Eastern Native Tree Society http://www.nativetreesociety.org Send email to [email protected] Visit this group at http://groups.google.com/group/entstrees?hl=en To unsubscribe send email to [email protected] -~----------~----~----~----~------~----~------~--~---
