The type of heat waves that wilt crops, torch forests — and kill people — are expected to become more frequent and severe over the next 30 years regardless of whether humans curb emissions of the greenhouse gas carbon dioxide, according to a new study.

These are heat waves akin to those that baked many regions of the U.S. in 2012 and devastated crops in Russia in 2010. Such bouts of extreme heat are so-called “three-sigma events,” meaning they are three standard deviations warmer than the normal climate of a specific region for weeks in a row. In the Russia event, for example, July temperatures in Moscow were about 12 degrees Fahrenheit warmer than normal.