The missing Medieval Warm Period is being discussed yet again over at Climate Audit. Since I have Bintanja and ver de Wal 2008 data which was meticulously calibrated to "today's" relative values, I thought of a quick post.
here with the Tierney et al 2010 data for Lake Tanganyika available at the NCDC-NOAA paleo website under Africa.I have two axis offset by 1 degree with the Tierney data in total period anomaly shifted downward. The Tsurf, is the surface temperature for ~45N and above and Tdo is the Temperature of the deep ocean. The "deep ocean" temperature and the Tierney reconstruction are close to in phase while the Tsurf is "hunting" a new set point.
The Tsurf bottoms at -16C relative to "today" just before 17,000 BC. BW estimate that the average temperature of the ~45N to pole area of the "Globe" was 16C degrees lower than today. This "regional" temperature depression was due to huge ice sheets in the high plains of the "high" latitudes, or latitudes north of 45N. Those high plains or steppes are farmland today and it took several thousands of years for the ice sheets to expand over the high plains without man clearing snow with plows, ash, peat and manure spreaders or in the case of some enterprising Russians, Mig jet engines mounted on tractors. If you want to blame man for warming, industry and agriculture above 45N would be the place to point.