Most major cities are now experiencing two more extreme heat streaks each year compared to 1970, according to an by Climate Central, which found that human-caused climate change is driving the trend.
The nonpartisan research group defines an 鈥渆xtreme heat streak鈥� as at least three days in a row where a city鈥檚 daily high temperature is hotter than 90% of all highs during the last few decades.
That鈥檚 happening even more frequently than the national average in several parts of the . Denver and Colorado Springs have experienced four more extreme heat streaks than they did 50 years ago. Phoenix and Tucson, Ariz., Cheyenne, Wyo., Helena, Mont., and Las Cruces, N.M., have three more streaks.
Research that when extreme heat lingers, the risk of heat-related illnesses rise, particularly for children, pregnant people, and .
Demand for cooling also surges, putting pressure on power grids, said Sean McKenna, a scientist at the Desert Research Institute in Reno, Nev.
鈥淗omes built in Reno, even in the 鈥�70s, really didn't have air conditioning because we didn't need it. We had cool evenings. We could cool the house off,鈥� McKenna said. 鈥淏ut if you look at a metro area now, like Las Vegas or Phoenix, you鈥檝e got to run the air conditioner all night long just to stay cool.鈥�
He said as energy-intensive cooling increases, so do the risks of power outages and blackouts, which can knock out air conditioners when needed most.
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