Reuters: Warmer weather and changes in atmospheric pressure may trigger headaches and migraines, rather than pollution, researchers said on Monday. A US research team showed that each temperature increase of 5 degrees Celsius — about 9 degrees Fahrenheit — appeared to increase the risk of severe headaches by nearly 8 percent compared to days when the weather was cooler. Air temperature, humidity and barometric pressure are often cited as a reason for headaches but until now there has …