Popping food into the microwave for a couple of minutes may seem utterly harmless, and Europe’s stock of these quick-cooking ovens emit as much carbon as nearly 7 million cars, a new study has found. And the problem is growing. With costs falling and kitchen appliances becoming “status” items, owners are throwing many microwaves after an average of eight years. This is pushing sales of new microwaves which are expected to reach 135 million annually in the EU by the end of the decade.

A study by the University of Manchester calculated the emissions of CO2—the main greenhouse gas responsible for climate change—at every stage of microwave, from manufacture to waste disposal. “It is electricity consumption by microwaves that has the biggest impact on the environment,” say the authors. The authors also calculate that the emissions from using 19 microwaves over a year are the same as those from using a car. According to the same study, efforts to reduce consumption should focus on improving consumer awareness and behaviour. For example, consumers could use appliances in a more efficient way by adjusting the time of cooking to the type of food.

However, David Reay, professor of carbon management, argues that, although microwaves use a great deal of energy, their emissions are minor compared to those from cars. In the UK alone, there are around 30 million cars. These cars emit more than all the microwaves in the EU. Backing this up, recent data show that passenger cars in the UK emitted 69 million tons of CO2 in 2015. This is 10 times the amount this new microwave oven study estimates for annual emissions for all the microwave ovens in the EU. Further, the energy used by microwaves is lower than any other form of cooking. Among common kitchen appliances used for cooking, microwaves are the most energy efficient, followed by a stove and finally a standard oven. Thus, rising microwave sales could be seen as a positive thing.