“Another indication of MWP and LIA being global“. Suddenly Anthony Watts likes temperature proxies because here they seem to go his way… In this case he’s been pointed toward a juicy Letter in Nature back in August of 2009 that proves that the Medieval Warm Period was global. At least in one place. OK then, what do we really have?
The denialist CO2 Science website (aka “Center for the Study of Carbon Dioxide and Global Change”, founded by a Peabody Energy operative) posted their own summary and “adapted” figure from the Nature Letter “2,000-year-long temperature and hydrology reconstructions from the Indo-Pacific warm pool.” It used Oxygen18 isotopes from planktonic foraminifera to estimate historical temperatures.
Strangely neither Anthony or CO2 Science provide a quick link to the claimed proof, but you can read the abstract here. Perhaps their coyness was triggered by the last sentence of the real abstract (emphasis mine)?
A companion reconstruction of 18O of sea water—a sea surface salinity and hydrology indicator—indicates a tight coupling with the East Asian monsoon system and remote control of IPWP [Indo-Pacific warm pool] hydrology on centennial–millennial timescales, rather than a dominant influence from local SST variation.
Although the authors also state that “Reconstructed SST was, however, within error of modern values” that doesn’t stop Anthony’s buddies from slapping a ruler on the “adapted” figure and declaring “we calculate that the Medieval Warm Period was about 0.4°C warmer than the Current Warm Period.“