Global warming will increase temperatures on hot summer days, potentially leading to more unhealthy "red alert" air pollution days in the coming years. Ozone pollution, commonly referred to as smog, can cause asthma and other respiratory illnesses, especially in youth and the elderly. The analysis was prepared by researchers at Yale, Johns Hopkins and Columbia universities, in collaboration with researchers at State University of New York at Albany and the University of Wisconsin-Madison. The 2007 study -- an expansion of the Heat Advisoryreport first issued by NRDC in 2004 -- profiles 10 new cities in the southern and eastern regions of the United States that could experience more "red alert" smog days, which can predispose the public to health risks, such as asthma attacks and hospitalizations from lung damage. On such days, the public should not partake in the usual summer outdoor activities. In order to protect public health, it is important that Congress address global warming through mandatory legislation that reduces global warming pollution on an order of 20 percent by 2020.