Installing a noisy, energy-sapping air conditioning unit is often considered a necessary evil for surviving humid summers, but air conditioning might be more evil than previously thought. While you think it’s cooling things down, it’s insidiously heating things up.

Cities will likely only grow hotter as a result of climate change and increased development. And that means that humans will demand more indoor cooling. But according to research published in the Journal of Geophysical Research: Atmospheres, excess heat generated by a city’s worth of air conditioners can increase the outside temperature by more than 1 degree Celsius at night.

When the study authors simulated the effect of air conditioner waste heat in four different scenarios in Phoenix, Arizona, even the model with a conservative estimate of air conditioning use increased nighttime temperatures by 0.25 to 0.5 degrees Celsius. A more realistic set of circumstances showed a change of 1 degree Celsius. After assuming that all spaces had some sort of air conditioning, the most extreme estimate of air conditioning prevalence, the model showed outside temperatures rising by as much as 1.5 degrees Celsius.

Study co-author and Arizona State University mathematician Alex Mahalov brought his summer energy bill to a televised interview on local news channel KAET TV to demonstrate how this difference can translate to dollars spent on household energy use. “One to two degrees matters,” he told host Ted Simon. “In July, the average temperature was one degree higher, and my bill is $30 more. So now if we have 1 million households in the state of Arizona, multiplied by 30, $30 million per month. In waste heat.”

Postdoctoral researcher Francisco Salamanca went on to explain that waste heat from air conditioners exacerbated the heat island effect, the phenomenon in which densely packed cities experience higher temperatures than similarly situated rural areas. If the heat island effect can increase temperatures by as much as 12 degrees Celsius, air conditioning units can make up as much as 2 degrees of that difference.

But the counterproductive air conditioning feedback loop doesn’t look totally hopeless quite yet. Salamanca and Mahalov pointed out that the same excess energy that makes our cities hotter could be captured and put to better use. It wouldn’t be that difficult, they say, to use wasted energy from AC units to heat water, or even help with cooking.