Differences in local temperatures can produce 45% swings in energy consumption per mile for electric vehicles and more than triple their associated carbon dioxide emissions, according to researchers at Carnegie Mellon University.

The CMU report points out that hot and cold climates can boost per-mile energy use both by affecting battery performance and raising the energy requirements to heat or cool the passenger cabin. It finds the lowest energy consumption occurs at an ambient temperature of about 70 F.

The study also reports that carbon dioxide emissions associated with generating power for the cars varies regionally by more than a factor of three because of variations in the mix of the local grid.

The analysis by researchers Jeremy Michalek and Tugce Yuksel appears in the American Chemical Society's journal Environmental Science & Technology. Their work correlates real-world performance of Nissan Leaf EVs in the U.S. with regional climate and power grid characteristics.

The CMU researchers say ambient temperature differences can reduce the average range of a Leaf nearly 36%. They say such regional swings, coupled with the local environmental impact of generating power to charge such vehicles, are big enough to affect adoption patterns and the energy/environmental implications of electrics compared with alternatives.