As temperatures rise around the country, school districts across the nation now have millions of added costs to install, upgrade, run and maintain cooling systems for classrooms.

The hottest time of the year — usually summer — is when school is out. But as climate change produces more frequent heat waves that are hotter, longer, and occur in spring and fall, school districts that did not even need air conditioning in 1970 have had to install them, and those with existing systems are having to increase capacity.

The number of days with temperatures over 80 F. has increased by as much as 30 days since 1970, especially in the South and Southwest, according to a report by the Center for Climate Integrity, which says that U.S. school districts will pay an additional $1.5 billion in costs annually to keep classrooms cool.

The report, Hotter Days, Higher Costs: The Cooling Crisis in America’s Schools examines just one cost of climate change, but one that is needed to maintain a productive learning environment in the nation’s schools. Ten states — California, Colorado, Illinois, Iowa, Massachusetts, Michigan, New Jersey, New York, Ohio, and Pennsylvania — will face more than $1 billion each in new cooling equipment costs by 2025. The 139 school districts that did not need air conditioning in 1970 will accrue between $50 million and $100 million each in cooling equipment costs by 2025, with 35 more spending at least $100 million, the report says.

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Based on the report by the Center for Climate Integrity, these are the states that are facing the highest costs to keep schools cool: