|Which most accurately describes the effects of climate change in the United States over the last 100 years?||a) temperatures have risen > 5° C|
No, this is incorrect.
Temperatures have gone through three modest cycles of warming and cooling and warming over the last 100 years. During the period 1915 to the early 1930s were increasing. Then from 1940 to about 1980 temperatures were decreasing. Temperatures then increased from 1980 to today where temperatures appear to have stabilized.
Overall, the total average annual temperature increase in the last century is relatively small and very uncertain, perhaps 0.7° C, although determination is difficult because it depends on which stations are used and how their data is adjusted for the urban heat island effect.
Source: Data used to calculate United States mean temperatures are from The United States Historical Climatology Network, specifically USHCN version 2 surface temperature data set. National Climate Data Center, National Oceanic and Atmospheric Administration.