In a recent paper () we reported finding a 65- to 70-year oscillation in each of the four records of observed global-mean surface temperature. We also found that the oscillation does not exist everywhere over the earth, but rather only over the North Atlantic Ocean and its bordering continental regions of North America, Europe, and northern Africa. We proposed three possible causes for our finding: (1) random radiative forcing of the climate system, that is, climatic noise, (2) oscillatory forcing external to the climate system, such as by a variation in solar irradiance, and (3) an oscillation internal to the climate system, perhaps not unlike that of the El Ni¿o-Southern Oscillation, but with a longer timescale. In this paper we critically examine the first hypothesis. Our analysis shows that this hypothesis can be rejected at a very high level of statistical confidence. ¿ American Geophysical Union 1995