Paper finds ~50% of warming over past 30 years was due to natural ocean oscillations

A paper presented at the NTU International Science Conference on Climate Change finds that the natural Pacific Decadal Oscillation [PDO] and Atlantic Multidecadal Oscillation [AMO] are responsible for about 50% of the warming observed over the past 30 years. According to the author, "In the past 30 years, the two multi-decadal oscillations contribute about half of the global mean surface temperature warming." Prior research has shown that solar activity changes were responsible for at least 50% of the observed warming over the past century. In addition, solar activity has been shown to influence ocean oscillations. Thus, most or all of the observed warming in recent decades can be attributed to natural causes.  

An Observational Analysis of Oceanic and Atmospheric Structure of Global-Scale Multidecadal Variability

Prof. Peng Liu ( Department of Atmospheric Sciences, Nanjing University of Information Science and Technology, China )

We aim to identify the multi-decadal variability relative to the global warming trend in available observation data. First we apply the Hilbert-Huang Transform (HHT) method to the global mean surface temperature (ST_gm) data to obtain a centennial global warming trend. Then the associated signals to the global warming trend are removed from three sets of climate variables including SST, ocean temperature from surface to 700 m, and the NCEP and ERA40 reanalysis, respectively. All detrended variables are low-pass filtered. Through three independent EOF analyses of the filtered variables, all consistently show two dominant modes with their respective temporal variability resembles the Pacific Decadal Oscillation/Inter-decadal Pacific Oscillation (PDO/IPO) and the Atlantic Multi-decadal Oscillation (AMO). The spatial structure of PDO-like mode is characterized by an ENSO-like structure and hemispheric symmetric features. The eigenvectors of AMO-like mode feature overall warm SST anomalies in the Atlantic and Pacific basin north of 10oS. The atmospheric structure associated with the AMO-like mode also exhibits hemispheric asymmetric features with anomalous warm air in Eurasia, and cold air over southern oceans. In the past 30 years, the evolution of PDO-like and AMO-like oscillations gives rise to strong temperature trends resembling negative-phase PDO mode in Pacific, and positive-phase AMO mode in Atlantic. Globally, the two multi-decadal oscillations contribute an important part of the ST_gm warming. The two oscillations are expected to slow down the global warming trends in the next decade.

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