Figure 4: Annual mean surface temperatures in the contiguous United States between 1895 and 1997, as compiled by the National Climate Data Center (12). Horizontal line is the 103-year mean. The trend line for this 103-year period has a slope of 0.022 ºC per decade or 0.22 ºC per century. The trend line for 1940 to 1997 has a slope of 0.008 ºC per decade or 0.08 ºC per century.