Mike,
the extended drought between 900 & 1300 AD just happens to coincide with the Medieval Warm Period, which is a period just about as warm today [a period that contained warm and cool as well as some wet and dry spells, of course]. The is work investigating the causes of this extended dry period and there is some thought that those conditions can occur again with global warming. neil On Jun 6, 6:02 am, "Mike Leonard" <[email protected]> wrote: > 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] -~----------~----~----~----~------~----~------~--~---
