by Andy May, May3, 2020 in WUWT
There have been recent discussions about ‘flattening the curve’ and some curves are easier to flatten than others. The Pages 2K Consortium calculates global mean temperature in a manner that flattens the long-term trend and makes present day temperatures appear warmer relative to past temperatures. Across the globe, temperature reconstructions show cooling millennial temperature trends with one exception, the Pages 2K global mean.
Millennial Temperature Trends Show Global Cooling
Global mean surface temperature anomalies were recently calculated by the Pages 2K Consortium led by Nuekom, 2019. Their statistical means are a conglomeration of seven different averaging methods for 7000 proxy records over the past 2000 years. The median across all global mean methods is plotted as a dashed line in Figure 1 and compared to Pages 2K’s published regional reconstructions. All means demonstrate similar trends as the median and will be simply be referred to as the global mean(s).
Regional temperature reconstructions are chosen that utilize similar proxy datasets used in the global mean calculation. The Arctic reconstruction by McKay incorporates a balance of proxy records consisting of ice cores, tree rings, lake and marine sediments north of 60 deg N. The Northern Hemisphere (NH) European reconstruction by Luterbacher is tree ring proxy based. And Stenni’s Antarctic reconstruction uses predominantly ice core isotopes.
The Pages 2K global mean appears to be reasonable compared to regional reconstructions from Present through the Little Ice Age (LIA) until about 1250 AD. Although it is difficult to see how the mean compares to regional reconstructions during the Present when using a 1961-1990 baseline as all reconstructions converge creating the “hockey stick” effect. Pre-1250 AD, the global mean appears to parallel NH Europe temperatures largely ignoring the Antarctic.