Bikers sought relief in the shade beneath the grandstands at the sun-scorched Roar on the Shore hub on Friday. In Waterford, historical re-enactor Bonnie Massing stripped down to her underwear — such as it was, an ankle-length petticoat and blouse — to cool off as temperatures hit 90 degrees Saturday at Waterford Heritage Days.

Those who did not cope wound up at UPMC Hamot literally sick with heat.

Like most of the U.S., the region sweltered on recent days. At Friday’s peak in Erie, the mercury registered 91 degrees, but the heat index, which combines heat and muggy humidity, reached 103 degrees.

Neither day broke a record. But that is not really the point. The point is, dog days like these — close, oppressive and dangerous — are happening more often and scientists say they only will get worse if we fail to act.

The Union of Concerned Scientists released a report Tuesday, “Killer Heat in the United States: Climate Choices and the Future of Dangerously Hot Days.” It offers temperature projections for each U.S. county depending on the extent to which we limit man-made heat-trapping emissions that are causing our planet to boil.

With no action, it says by mid-century Erie County would experience an average of 24 days per year with heat index temperatures of 90 degrees, four days above 100 degrees and one day above 105 degrees. By the century’s end, those numbers would jump to 58, 19 and nine days, respectively.

A Climate Central report released in April examined 242 cities and found average temperatures have risen in nearly 98 percent of them since 1970. Erie was listed at the eighth fastest-warming, with temperatures increasing 4.06 degrees between 1970 and 2018.

It is neither just the heat nor the humidity that should alarm, but all that goes with the warming planet. That includes the extreme storms that have battered the region. While Erie sizzled Friday and Saturday, points just to our south experienced both intense heat and damaging deluges of the sort that in 2018 took a $126 million toll on roads and other infrastructure in Pennsylvania.

The heat, the storms, the flooding, the changes to the environment, including harmful algae blooms fueled by polluted storm runoff and warming Lake Erie waters, don’t just affect health. They threaten key industries here from farming to tourism.

The Concerned Scientists report says we have a narrow window to change course and perhaps retain something closer to the summer days we know and love. Pennsylvania’s Climate Action Plan is one of many resources pointing the way forward — solar and wind power, electric vehicles, public transit and other strategies to reduce greenhouse gas emissions.

This is not something we can or should simply sweat out.