As droughts hit the American West over the last several years, people often think about parched crops, lower water levels and even a kindling-dry landscape suitable wildfires. One thing that is often overlooked are the impacts droughts have on hydroelectric power plants and their hindrance on greenhouse gas reductions.

A recent Stanford University study finds that 10 percent of the total carbon dioxide generated from California, Oregon, Washington and Idaho for electricity generation in the 21st century is the result of states increased reliance on fossil fuels when water was too scarce to turn electrical turbines at dams.

As climate change grips the world, higher temperatures and more severe droughts could spur greater greenhouse gas emissions in these dry times.

According Noah Diffenbaugh, a climate researcher at Stanford and co-author of the study:

“There has been some sense and some published work showing that droughts affect emissions. But what hasn’t been clear is exactly how significant these droughts are. Meeting these state-level climate mitigation goals is made a lot more difficult.”

The study found that the turn towards fossil fuel-generated electricity during droughts accounted for an extra 100 million tons of carbon dioxide throughout 11 states in the Western United States between 2001 and 2015, which is equivalent to adding around 1.4 million cars to the roads.