The world at large also can do its part by limiting emissions, health experts say. Average global temperatures already have increased by nearly 2 degrees Fahrenheit since preindustrial times. The extent to which future warming can be limited will have a direct impact on human health, University of Bristol researchers found in a June study. If the increase is kept within one more degree, Philadelphia and 14 other U.S. cities would save hundreds of lives a year, compared with the death toll if average temperatures increased by 3 more degrees, the authors found.