A controversy has existed the past several years over whether or not the earth's atmosphere is warming. Data taken from thermometers near the earth's surface reveal a quite convincing warming trend of about 0.5 K over the last 100 years. On the other hand, data from Satellites suggest the lower atmosphere is cooling, not warming. Wentz and Schabel (1998) report that corrections to satellite-based temperature measurements are needed to account for the slow decrease in altitude that satellites normally experience due to drag. Spencer and Christy (1990, 1992) and Christy et al. (1994) reported a 17-year cooling trend in satellite (microwave sounding unit, MSU) temperature of - 0.05 K per decade globally at 3.5 km. As the satellite falls toward earth, its field of view changes and produces a reading representative of a more limited area. The corrected temperature calculated by Wentz and Schabel (1998) for the period analyzed by Spencer and Christy is +0.07 K per decade, which is much more consistent with the observed rise in global surface temperature of 0.13 K per decade (Houghton, 1996) over this 17-year period.
References
Spencer, R. W., and J. R. Christy, 1990: Precise monitoring of global temperature trends from satellites. Science, 247, 1558-1562.
Spencer, R. W., and J. R. Christy, 1994: Precision and radiosonde validation of satellite gridpoint temperature anomalies Part II: A tropospheric retrieval and trends during 1979-90. J. Climate, 5, 858-866.
Christy, J. R., and R. T. McNider, 1994: Satellite greenhouse signal. Nature, 367, 325.
Houghton, J. T., et al. 1996: Climate change 1995: The science of climate change. Cambridge Univ. Press.
Wentz, F. J., and M. Schabel, 1998: Effects of orbital decay on satellite-derived lower-tropospheric temperature trends. Nature, 394, 661-664.