IPCC Fourth Assessment Report: Climate Change 2007
Climate Change 2007: Working Group I: The Physical Science Basis

Figure 3.38. Annual probability distribution functions for temperature indices for 202 global stations with at least 80% complete data between 1901 and 2003 for three time periods: 1901 to 1950 (black), 1951 to 1978 (blue) and 1979 to 2003 (red). The x-axis represents the percentage of time during the year when the indicators were below the 10th percentile for cold nights (left) or above the 90th percentile for warm nights (right). From Alexander et al. (2006).