Two Amerindian demographic shifts are attributed to climate change in the northwest plains of North America: at approximately 11,000 calendar years before present (yr BP), Amerindian culture apparently split into foothills-mountains vs. plains biomes; and from 8,000-5,000 yr BP, scarce archaeological sites on the open plains suggest emigration during xeric "Altithermal" conditions. We reconstru...

Mann et al. (1) present two paleoclimate reconstruction methods [‘‘error-in-variables’’ (EIV) and ‘‘composite plus scale’’ (CPS)], claiming statistically significant skill for both. Their figure 3 reveals that from approximately 750 to 1100, the CPS 95% confidence interval excludes the EIV 95% confidence interval and vice versa. This is evidence not of skill, but of inconsistency. Contrary to a...

Equilibrium climate sensitivity (ECS)—the rise in global mean surface temperature (GMST) resulting from a doubling of atmospheric carbon dioxide (CO2) concentration, once the ocean has reached equilibrium—is a key climate system parameter. Effective radiative forcing (ERF) provides a metric, designed to be a good indicator of their impact on GMST, of the effects on the Earth’s radiative imbalan...