Graduate student Joe Fitzgerald will lead a discussion of a recent PNAS paper by Tung and Zhou entitled, "Using data to attribute episodes of warming and cooling in instrumental records" (supplementary material).

"The observed rate of global warming fluctuates over time, and attempts are frequently made to provide physical explanations for these variations in warming. Tung and Zhou suggest that internal climate variability associated with the Atlantic Multidecadal Oscillation (AMO) modulates the observed warming rate on 50-80 year timescales. Identifying the contribution of the AMO to the observed warming trend is difficult, as long records are required to quantify the AMO variability. Tung and Zhou use the long record of Central England Temperature as a proxy for the AMO and make a new estimate for the temperature trend after subtracting out internal variability, including the AMO signal. Their results suggest that the AMO has substantially influenced our estimates of the temperature trend, and that the corrected rate of warming has been nearly steady at .07-.08 C / decade since 1910."