A group at the University of Arizona is using new tree ring techniques to try to crack one of the interesting outstanding paleoclimate questions in the Southwest – the summer monsoon. Tree rings have long been used to reconstruct winter precipitation records (fat rings = wet years, thin rings = dry years), but the summer rains have been a harder nut to crack. Jessica Conroy had a nice writeup recently on the new work:
Some interesting results so far are that the 20th century has been somewhat unique compared to the last 350 years in that there weren’t any periods of persistently dry monsoons—meaning several years in a row of weak monsoons.
Before the 20th century, there were more periods of dry monsoon after dry monsoon, especially in the 1880s up until about 1905.
Dan Griffin, who’s doing the work, has some more on his page. And if you want to learn more about tree rings and tracking past climate, you should buy my book, The Tree Rings’ Tale: Understanding Our Changing Climate. (There’s a chapter on Connie Woodhouse, Dan’s thesis advisor.)