People that make a living at this know this from satellites, weather balloons, thermometers, weather stations and a lot more data generating stuff.Since 1880, average global temperatures have increased by about 1 degrees Celsius (1.7° degrees Fahrenheit). Global temperature is projected to warm by about 1.5 degrees Celsius (2.7° degrees Fahrenheit) by 2050 and 2-4 degrees Celsius (3.6-7.2 degrees Fahrenheit) by 2100.2
According to the National Oceanic and Atmospheric Administration (NOAA) [exit DNR], average annual global temperatures have increased steadily since the 1960s.
Nineteen of the 20 warmest years have occurred since 2001. It is likely that the coldest year moving forward will be warmer than the warmest year that we experienced in the 20th century.
All the above is from years of study the Wisconsin Dept of Interior in collaboration with the University of Wisconsin.
