The temperature on a hot summer day in a single city can vary by as much as 11 degrees Celsius depending on where you are—whether you’re near green spaces that cool down the surrounding areas, or pavement and concrete, which absorb heat and radiate it. That’s the heat island effect, and mapping it is the focus of a project led by Portland State University researchers, funded in part by NOAA, and conducted by on-the-ground volunteers who have been taking temperature measurements across a number of U.S. cities. Those measurements have been cross-referenced with other data about the neighbourhoods, which will help cities figure out how to keep their citizens cool during heat waves—which, let’s face it, are going to be a lot more common going forward. National Geographic, New York Times.