Trends over the Past Century

One of the obvious manifestations of anthropogenic emissions is expected to be an increase in the temperature of the air and sea surface (SST). As a result, there have been many analyses of such temperatures, for which there are substantial records based on instrumental measurements made in a number of locations 

While the surface temperatures have clearly been increasing, some satellite measurements have suggested that the air temperatures in the troposphere have been cooling at altitudes where this was not expected. However, this is controversial (e.g., Pielke et al., 1998a, 1998b). For example, Wentz and Schabel (1998) have shown that the loss of satellite altitude with 

FIGURE 14.57 Global average temperature anomaly (AT) for land and sea surface measurements relative to the period from 1961 to 1990 (adapted from IPCC, 1996). 

The five warmest years for which there are surface temperature records have all been since 1990 (Jones et al., 1998), with the most recent year for which there are data (at the time of writing), 1997, being the warmest in the past century (see Kerr, 1998, and references therein). Mann et al. (1998) have used a variety of indirect indicators for temperature (e.g., ice core data see later) over the past 600 years in the Northern Hemisphere and report that mean annual temperatures for three of the eight years up to and including 1995 are higher than any since 1400 A.D. 

FIGURE 14.58 Global nonurban annual average temperature anomalies for the (a) maximum temperature, (b) minimum temperature, and (c) diurnal range of temperatures from 1950 to 1993 for 4100 stations in both the Northern and Southern Hemispheres (adapted from Easterling et at., 1997). 

---