Global Temperature Trends Adjusted for Unforced Variability

Multidecadal climate variability has proven difficult to deal with when estimating temperature trends. This possible unforced internal oscillation of the climate system provides an opportunity to correct temperature trends. The Atlantic Multidecadal Oscillation (AMO) is proposed as a potential index for this unforced variability. The AMO pattern does not appear to correspond to forcing histories used by the IPCC. Subtracting a scaled version of the AMO from the Hadley global temperature data produced damped decadal-scale fluctuations in the temperature data. The adjusted dataset is highly correlated with the anthropogenic forcing history from IPCC AR5. The linear post-1970 temperature trend is 0.83℃/century vs. 1.63℃/century for the raw data. Thus almost exactly half of the post-1970 warming is possibly natural. The use of the AMO as an index of unforced variability is supported by the fact that subtracting it simplifies the temperature response by damping the peaks and troughs consistently.