Natural signals in the MSU lower tropospheric temperature record

Volcanic and ENSO forcings explain nearly two-thirds (63.5%) of the varianc e in monthly global temperature anomalies in the MSU lower tropospheric tem perature observations from 1979 through 1999. While the raw trend in the dr ift-adjusted 1979-99 global data is a statistically significant warming of 0.055 degrees C/decade, the combination of volcanism and ENSO account for 2 5.4% of this trend, or 0.014 degrees C/decade. The remaining trend, 0.041 d egrees C/decade, is left unexplained, likely comprising a combination of fa ctors including the anthropogenic alterations to the collection of the eart h's greenhouse,oases, solar variability, and other forcings internal to the earth/atmosphere system. A recent widely cited attempt to explain the disc repancy between the rate of the observed increase in lower tropospheric MSU temperatures and the much larger value predicted by general circulation mo dels weakens considerably when the known natural forcing mechanisms are mor e completely specified.