DO BIDECADAL OSCILLATIONS EXIST IN THE GLOBAL TEMPERATURE RECORD

MODELS predict 1-3 that increasing atmospheric concentrations of greenhouse gases will result in an increase in the global mean temperature over the next few decades and beyond. It is therefore important to be able to distinguish a warming trend from natural variability in the time series of global temperatures. Recently, Ghil and Vautard 4 applied singular spectrum analysis to a record of global surface air temperatures, and identified a secular warming trend and a small number of oscillatory modes. The oscillations had interdecadal periods of 21 and 16 years (attributed to changes in the extratropical ocean circulation), and interannual periods of 6 and 5 years (attributed to the El Nino/Southern Oscillation). Here we re-analyse the data by considering various lengths of the temperature record, and we apply singular spectrum analysis to five other temperature records (two global, three hemispheric). Our results offer no support for the presence of bidecadal oscillations in the global surface temperature records.