Patterns of Climate Change across Wisconsin from 1950 to 2006

Trends in meteorological and ecological variables were calculated across the state of Wisconsin from 1950 to 2006 to quantify recent patterns of climate change. In summary, annual average nighttime low temperatures have increased by 0.6 to 2.2o C, whereas the annual average daytime high temperatures have warmed by 0.3 to 0.6o C. Annual average precipitation has increased by 50–100 mm in the central and southern portions of the state, about a 10–15% increase, while precipitation across the far northern portion of the state appears to have declined by 20–60 mm since 1950, with the most pronounced decrease occurring during summer. On a seasonal basis, warming temperatures are more pronounced during winter and springtime, and nighttime temperatures are warming faster than daytime high temperatures. Some cooling trends in daytime high temperatures were observed during late summer and fall, particularly in the northeast and far southwest portions of the state. We calculated that the length of the growing season has increased by 5 to 20 days, with the greatest change in the central and northern part of Wisconsin. The annual number of days each year with low temperatures less than 0o F (–17.8o C) has diminished substantially, while the number of days each year with highs greater than 90oF (32.2o C) has remained relatively constant. A slight shift northward of the ecological “Tension Zone” was also documented. [