CO2 Sensitivity and Climates of the Past


As the potential impacts of anthropogenic warming have become clearer, 
paleoclimate studies have become less focused on understanding climate 
in Earth history per se, and more geared toward identifying processes and 
impacts that could come into play and affect modern society over the 
coming centuries. To that end, past warm intervals such as the Pliocene 
and Eocene have become become magnets for proxy studies, mostly 
geochemistry-based, designed to quantify a variety of climate indicators 
(e.g., SSTs, terrestrial temperatures and precipitation) as well as past 
levels of CO2. Underlying these efforts is the assumption that CO2 is the 
main internal driver of Earth's climate, and that the relationship between 
CO2 levels and global climate conditions has a certain sensitivity.
In this talk, I'll review how and what we know about the relationship 
between past CO2 levels and climate, how well we know it, and the 
results of some recent work on the Pliocene that suggests (perhaps not 
surprisingly) that CO2 and climate sensitivity may be a more complicated 
matter than previously thought. This latest study also raises the question 
of whether we are missing part of climate's "big picture" that's needed for 
future climate work.