Abstract
CO2-induced changes in the interannual variability of monthly surface air temperature and precipitation are studied using 19 model experiments participating in the second phase of the Coupled Model Intercomparison Project (CMIP2). The magnitude of variability in the control runs appears generally reasonable, but it varies a great deal between different models, almost all of which overestimate temperature variability on low-latitude land areas. In most models the gradual doubling of CO2 leads to a decrease in temperature variability in the winter half-year in the extratropical Northern Hemisphere and over the high-latitude Southern Ocean. Over land in low latitudes and in northern midlatitudes in summer, a slight tendency toward increased temperature variability occurs. The standard deviation of monthly precipitation increases, on average, where the mean precipitation increases but also does so in some areas where the mean precipitation decreases slightly. The coefficient of variation of precipitation (i.e., the ratio between the standard deviation and the mean) also tends to increase in most areas, especially where the mean precipitation decreases. However, the changes in variability are less similar between the 19 experiments than the changes in mean temperature and precipitation, at least partly because they have a much lower signal-to-noise ratio. In addition, the changes in the standard deviation of monthly temperature are generally much smaller than the time-mean warming, which suggests that future changes in the extremes of interannual temperature variability will be largely determined by the latter.
Corresponding author address: Dr. Jouni Räisänen, Rossby Centre, SMHI, S-60176 Norrköping, Sweden. Email: jouni.raisanen@smhi.se
