Absolute Values
 

20th Century Trend Maps

Figure 10: Time histories of the changes in (a) annual average temperature (oF), and (b) annual total precipitation (inches per year) for the 20th century based on observations and on simulations from the Canadian and Hadley models, calculated as 10-year running means from 1900 to 2000. Mean temperature is the actual mean temperature from the models, rather than the mean of the minimum and maximum temperatures.  Anomalies with respect to 1961-1990.  In these simulations, unlike in intercomparisons of the atmospheric models as in the AMIP project (Gates et al., 1999), the ocean temperatures are freely calculated and the concentrations of greenhouse gases and aerosols are being imposed; natural forcings such as by changes in solar radiation and volcanic eruptions that are likely affecting the observed climate are not, however, being treated in the models because observations of their precise radiative influences are not available.