There’s more than one way to cut emissions. Swapping conventional cars for electric ones might cut emissions from cars, but it may also help cities like Beijing beat the heat, further lowering emissions of carbon dioxide by cutting the use of air conditioning.
The role of electric cars in combating climate change is hotly debated, because although they might emit less greenhouse gas directly, they are more expensive and cause more pollution than conventional cars during the manufacturing process. But it seems there may be hidden benefits to them.
Electric cars emit less than 20 per cent of the heat that conventional cars do, thus contributing less to the phenomenon of cities being warmer than the surrounding areas, known as the urban heat island effect.
If this lowers temperatures, use of air conditioning would also drop, and so would the energy used to power it, argues a team led by Canbing Li from Michigan State University in East Lansing.
Using summer 2012 in the Chinese capital of Beijing as an example, the team estimate that replacing conventional cars with electric ones could have reduced the heat by nearly 1 °C. That in turn would result in a reduction in air conditioning use in the city, leading to a drop of 10,686 tonnes in daily CO2emissions.
“I was surprised by the level of decreased energy consumption of air-conditioning,” says Li.
The team says that there are several factors contributing to the urban heat island, and not all have been addressed in the study. This makes some people sceptical about the estimates.
“Investigating a mitigation strategy is much more complicated than just considering the heat flux,” saysAli Gholizadeh Touchaei of the Heat Island Group at Concordia University in Montreal, Canada. “The sophisticated relation between moisture balance, effect of wind, and interactions of buildings and atmosphere should be accounted for.”
And Oscar van Vliet of the Swiss Federal Institute of Technology in Zurich says that our heat emissions are only partly responsible for the heat island effect, it is also down to the city retaining that heat thanks to tarmac surfaces, which don’t cool down quickly.
Cars of the future
Regardless of how big any cooling effect might be, the climate effects of urban transport merits further study with more sophisticated models, say other researchers.
“It is an interesting study, as the issue of heat generated by vehicles isn’t something that has been thought about in great detail,” says Timothy Johnson of Duke University in Durham, North Carolina.
It could become an ever bigger influence as electric cars catch on. Johnson expects the vehicles to dominate the transportation market in a few more decades once they overcome the technical challenges of driving range and battery charging infrastructure.
Unlike with conventional cars, which depend on non-renewable fuels, the disadvantages of electric cars can be overcome, says Li.
Journal reference: Scientific Reports, DOI: 10.1038/srep09213
Clarification, 20 April 2015: The amount of heat generated by electric cars has been clarified since this article was first published.