Page 59

image

Figure 9.1
Global-mean seasonally averaged tropospheric time series based on the same
MSU 2LT measurements (Christy et al., 2000). The red curve represents full 
global coverage, while the pink curve is based on a limited sampling of grid points 
designed to mimic the existing distribution of radiosonde stations. The dark gray
curve (bottom) represents the difference between the sampled and full data sets. 
The light gray lines represent the means of each time series. The first season is March–
May 1979 and the last season is December 1998–February 1999. The sub-sampled 
MSU data were supplied by the U.K. Meteorological Office (UKMO).

principle, a close match constitutes an independent verification of the MSU data. The two curves, shown in Figure 9.2, exhibit a number of common features and rather similar trends.

Uncertainties exist in assigning confidence levels to trends because of persistence in the data, which may or may not be due to the trend itself. There is no unique set of confidence intervals for the relatively short atmospheric temperature time series considered here. The estimated confidence intervals depend on the underlying statistical model that is used to describe the data, as well as on the exact period considered and the sampling interval (i.e., whether one uses monthly, seasonal, or annual means). One approach, following Cryer (1986), yields trends of 0.14 ±0.10 °C/decade for the subsampled MSU data and 0.04 ±0.07continue



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement