Here we briefly discuss the radiative forcing estimates used for understanding climate during the last millennium, the mid-Holocene and the Last Glacial Maximum (LGM)(Section 9.3) and
in estimates of climate sensitivity based on palaeoclimatic records (Section 9.6.3).
Recently a new model - based paper on climate sensitivity was published by Kate Marvel, Gavin Schmidt (the head of NASA GISS) and others, titled «Internal variability and disequilibrium
confound estimates of climate sensitivity from observations».
To better assess confidence in the different
model estimates of climate sensitivity, two kinds of observational tests are available: tests related to the global climate response associated with specified external forcings (discussed in Chapters 6, 9 and 10; Box 10.2) and tests focused on the simulation of key feedback processes.
That a robust behaviour in models of apparent (effective) climate sensitivity being lower in the early years after a forcing is imposed than subsequently, rather than remaining constant, requires multiplying
estimates of climate sensitivity by a further factor of ~ 1.25 in order to convert what they actually estimate (effective climate sensitivity) to ECS.
Caps will error because (1) they won't cover some major emitters for decades, (2) they won't cover land - use changes, (3) the best
scientific estimate of climate sensitivity is uncertain by hundreds of billions of tonnes, (4) the earth's CO2 uptake by 2 ° target date is highly uncertain.
However, the point of this posting is to convince those WUWT readers, who, like Einstein, need a physical analogy before they will accept any mathematical abstraction, that the atmospheric «greenhouse» effect is indeed real, even
though estimates of climate sensitivity to doubling of CO2 are most likely way over-estimated by the official climate Team.
The reason why a 1 / S ^ 2 prior is noninformative is that
estimates of climate sensitivity depend on comparing changes in temperature with changes in -LCB- forcing minus the Earth's net radiative balance (or its proxy, ocean heat uptake)-RCB-.
«the long fat tail that is characteristic of all recent
estimates of climate sensitivity simply disappears, with an upper 95 % probability limit... easily shown to lie close to 4 °C, and certainly well below 6 °C.»