AGW claim of no MWP in the southern hemisphere is debunked ... again

24 May 2011

At ... this post is based on a paper published last week in PNAS on research in South America and appears to show, and indeed it does show quite transparently that warmth in the northern hemisphere coincides remarkably well with lower precipitation in the Peruvian Andes. A sediment core taken from a lake displays evidence of big swings in rainfall levels. In addition, geological records from the Quelccaya glacier, various caves, the Cariaco Basin and knowledge of the annual position of the Intertropical Convergence Zone were combined with the evidence gleaned from the sediment core. Most notable was the amount of rainfall in Peru that peaked around 550AD. This is remarkable confirmation of the low growth tree ring event found by Mike Baillie and implies a serious ecological event of some kind that included a brief cold spell in NW Europe that coincided with cooler and very wet conditions in Peru. However, confirmation of the MWP (the medieval warm period) comes from low levels of precipitation that kicked in around 900AD and lasted unabated for the next 300 years. The climate became drier and the authors of the paper suggests this coincided with droughts and a decline in human population in some parts of the Americas - but a broader view might differ in that it just confirms the MWP and not necessarily the cause of the droughts. After 1300 it became wetter but the wettest phase was the Little Ice Age between 1500-1750AD - (long term wet phase). There was a brief dry period between 1820-40 but wet and cool conditions returned - but after 1900, and this is a broad perspective, drier conditions set in (thereby adhering to the AGW alarmism that probably bank rolled the research). The weather, no doubt has become somewhat drier, as it did in the MWP, but the will it get as dry as the obligatory alarmism predicts? As no sudden hockey stick blade uplift in dryness was detected in the late 20th century, the peak of global warming in the data, we can safely assume, it will not.