The western U.S. was hit with a historic heat wave last week, with many areas seeing temperatures 20 to 30 degrees above normal.
Denver broke its record for the hottest March day three days in a row. Four locations reached 112 degrees Fahrenheit, surpassing the previous U.S. high for March of 108 degrees.
Aspen hit a record 75 degrees on Friday, compared to its daily average of 47 degrees.
A study released Friday found the heat wave would have been “virtually impossible” without human-induced climate change.
“The heat wave that's happening across the West right now is mind blowing from a climate perspective,” said Kristina Dahl, vice president of science at Climate Central, on Thursday. “We're seeing temperatures that are more typical of June or July across pretty much the western half of the country.”
Climate Central is a policy-neutral nonprofit that researches and communicates insights and observations about the changing climate.
One of their offerings is an interactive database called the Climate Shift Index, which tracks the influence of climate change on day-to-day temperatures worldwide.
Attribution science has come a long way in recent years, and scientists can now say with a high degree of confidence how much climate change contributed to a given event.
For the Climate Shift Index, Dahl and her team compare the probability of a temperature occurring in the real world to the probability of that temperature occurring in a world without human-induced greenhouse gas emissions.
“We look at the actual world we're living in and the temperatures we're experiencing, say, today, and then we can model what the world would be like without climate change,” Dahl explained.
Throughout last week, the majority of the West was at level 5 — the highest category. The unseasonal heat was at least five times more likely due to human-caused climate change.
The early timing of the heat wave also creates an added health risk.
Dahl said people are more vulnerable to heat stress when their bodies haven’t adapted to warm summer temperatures yet.
“So the same magnitude of heat wave in March or April typically sends more people to the emergency room than the same magnitude of heat wave if it happens in September or October,” Dahl said.
The heat wave is also bad news for Colorado’s already historically low snowpack.
“Any snow that we have on the ground is likely going to be decimated,” Dahl said. “Even in the California Sierras, which have had some snow this year, we're expecting that to get eroded quite a bit by this heat wave. And obviously any precipitation we'd be getting, if it's warm, it's going to fall as rain rather than snow.”
Less snow now means less water during the summer dry season, Dahl said.
That puts an added strain on farmers trying to irrigate crops, and allows vegetation to dry out faster, becoming fuel for wildfires.
