INVESTIGATING THE ORIGINS AND SIGNIFICANCE OF LOW-FREQUENCY MODES OF CLIMATE VARIABILITY

An analysis of the 130-year record of the Earth's global mean temperature reveals a significant warming trend and a residual consistent with an autocorrelated (''red'') noise process whose predictability decays with a timescale of two years. Thus global temperatures, in isolation, do not indicate oscillations at 95% confidence against a red noise null hypothesis. Weak signals identified in the global series can, however, be traced to significant sea surface temperature oscillations in the equatorial Atlantic (period approximately 10 years) and the El Nino region of the Pacific (3-5 years). No robust evidence is found in this data for interdecadal oscillations. The 10-year Atlantic oscillation corresponds to a pattern of temperature anomalies which has been associated with interannual variations in West African rainfall and in U.S. hurricane landfall frequency.