On another episode, we told you about urban heat islands. Buildings and asphalt absorb summer heat -- from sun and air, cars and trucks, power plants and air conditioning -- and hold it, driving city temperatures far higher than surrounding areas, sometimes to devastating effect.

Urban heat islands have killed thousands. But new studies of over 3,000 cities around the world show they’ve saved many more! That’s because heat islands also hold heat in winter, as buildings, transportation and industry ‘leak’ heat into the environment.

The result, just as in summer, is that cities can be 10 degrees Fahrenheit warmer. That means less energy required for heating homes and buildings. And, it means many fewer deaths from hypothermia, heart attacks and respiratory illness.

The studies show that, in the global average, urban heat islands saved four times as many lives in the winter as were lost in the summer. In cold climates, it was 11 times as many!

Tropical cities may not enjoy these benefits – since their winters are not cold enough to kill. But overall, this suggests city planners should adapt regionally to urban heat islands.

Warmer cities should try to mitigate heat effects... while colder cities may want to encourage them!

Cities that experience both temperature extremes – and many do – may investigate changing roof colors and other flexible solutions that could reflect heat in summer, and absorb it in the winter. Changing, like nature, with the season.