Those who question the environmental benefits of electric vehicles over their gas-guzzling brethren often point out that the electricity powering EVs usually comes from fossil fuel-burning power plants. But a study conducted by researchers at Michigan State University (MSU) and Hunan University in China has revealed some hidden benefits of EVs, regardless of where the electricity originates.

Most people will have witnessed the heat haze above a line of traffic stuck on a freeway in summer. These vehicles are contributing to the urban heat island effect. This in turn results in city dwellers cranking up the office and home air conditioning, which in turn further adds to the outdoor heat and sends electricity usage northwards.

The study, led by Professor Canbing Li, found that electric vehicles could help mitigate both of these related problems. With electric vehicles emitting only around 20 percent of the heat that a gasoline vehicle produces, swapping them with gas vehicles could significantly reduce the temperature in a city, thereby reducing air conditioner usage.

They calculated that in the summer of 2012, switching vehicles from gas to electricity could have reduced the urban heat island intensity by almost 1° C (2.8° F) in Beijing, which would have saved the city 14.4 million kWh of electricity from reduced air conditioner usage and cut CO2 emissions by 11,779 tons per day.

"It's easy not to see the big picture on issues like electric cars and global warming, but when we look with a holistic approach, we find these unexpected connections," said study co-author Jianguo "Jack" Liu, who holds the Rachel Carson Chair in Sustainability at MSU. "Heat waves kill, and in terms of climate change, even one degree can make a difference."

However, the authors admit that not all factors that can influence the urban heat island effect were addressed in the study. For example, the impact of reduced aerosol pollution on heat island intensity was subject to conflicting reports.

The team's study appears in the journal Scientific Reports.