Millar and Friedlingstein find a transient climate
response of 1.84 C / TtC using the Cowtan and Way
temperature record, 2.05 C / TtC using the Berkeley Earth
temperature record, and a
median estimate of 2.11 C / TtC using CMIP5 ESMs (though with a wide range from 0.8 — 2.5 C / TtC).