"Well, where does the electricity come from?" they ask. Familiar with it? Most of us have pre-prepared figures as to why EVs are cleaner, even considering the fuel burned to make the electricity.
Unless you live in China, where they really could be dirtier than running an internal combustion-engined vehicle.
As with many developing nations, the bulk of China's electricity is created by burning coal, one of the dirtiest ways of generating power. As a result, charging your electric car in China results in greater CO2 emissions than simply fuelling up a gasoline car and burning dino juice.
The figures have been calculated by La Paz-based consultancy Gruetter Consulting. Gruetter is one of the companies developing projects to help reduce greenhouse gas emissions under the United Nations' Clean Development Mechanism (CDM), producing detailed information on how much CO2 equivalent every project will save.
In India this involves a project to replace many of the dirty internal-combustion scooters with electric equivalents - 1.5 million of them over the next ten years, in fact. This should save 1.5 million tons of CO2 equivalent. In China though, this isn't possible due to the huge grid emissions. Even running an electric scooter would produce 20g/km more CO2 equivalent than a regular gasoline version.
For cars, this would be even worse, thanks to the extra energy needed to "fill" them with electricity.
It's a situation worth remembering if you live in a region where electricity production is largely coal-fuelled. EVs are generally the cleaner option and local emissions will always be lower, but outright emissions are still dictated by the power station generating your electricity...