Mind your data, warn atmospheric scientists

17 Jun 2002

Computer models and temperature-gleaning satellites are useful tools in the quest to diagnose global change, but only when their limitations are well understood. Thisis the message conveyed by two scientists in articles appearing this week in the journal Nature. One article provides new findings on an ongoing controversyinvolving the reliability of global temperature trends obtained via satellite. The other provides an overview of how to use--and how not to use--computer models thatmimic the earth's atmosphere for research on climate change.

A puzzling discrepancy between global temperature trends ascertained by surface instruments versus satellites is analyzed by NCAR's James Hurrell and KevinTrenberth in the article "Spurious trends in satellite MSU temperatures from merging different satellite records." Since 1979, microwave sounder units (MSUs) havebeen deployed aboard polar-orbiting satellites of the National Oceanic and Atmospheric Administration. MSUs measure the brightness of oxygen in the earth'satmosphere and thus infer the temperature across the globe at various heights.

Some popular press articles now cite only the MSU or only the surface data in reporting on global temperature trends, without noting the counterpart to each. Hurrelland Trenberth stress that both data sets are needed to unravel the mysteries of global climate. "The MSU data are excellent for analyzing year- to-year changes, but notnecessarily for longer-term trends," says Hurrell.