The chart above, which has been provided by the Intergovernmental Panel on Climate Change Third Assessment Report, shows that temperatures in the northern hemisphere have been increasing since the 1900s. Despite the increase over the last 100 plus years, there was a slight drop in temperatures around the 1980s. However, since then the average temperature in the northern hemisphere has been increasing. The National Oceanic and Atmospheric Administration reports that in 2012 alone, Michigan has had 12 record high heat days.
The above chart shows the average yearly temperature in Michigan from 1895 to 2012. While there have been several ups and downs over the last 117 years, the average temperature to date in 2012 has proved to be the highest at 48.49 degrees. This figure, however, only takes the months January through July into consideration. The highest full yearly average in recent history was 46.93 degrees in 1998. The average yearly temperature in 2011 was about 4 degrees lower than the 1998 average.
The above chart shows average temperatures for May, June and July from 1980 to 2012. While the average temperatures over this time span do not show a consistent pattern, there is evidence that in recent years the average temperatures have been increasing. For example, for the month of July there was about a 10 degree average increase from 2009 to 2011; the climate then leveled off from 2011 to 2012. In May, there was an increase from 2008 to 2010 and in June there was an increase from 2009 to 2010.
The above charts show that not only have temperatures in Michigan been above average, but so have the water temperatures of the Great Lakes. Lakes Superior, which is the largest and deepest of the lakes, has experienced the highest above average temperatures of the five lakes. Lake Huron and Lake Erie (the smallest and shallowest) have experienced the least fluctuation from the average temperatures they have experienced in years past (1992-2011). The elevated water temperatures can be attributed to the higher air temperatures that Michigan and the Midwest region have been experiencing this year.