this includes just three cities in north america -- calgary,, vancouver, and san frarancis. list of f cities where it coud be too hot is staggering. rome, tokyo,adrid, new york, chicago, los angeles, and the list goes on. extreme high temperatures have impacted the athletic world. in 2007, high heat forced the cancellation of the chicago marathon. at the trials in los angeles, 30% of the runners dropped out of the race due to the heat. and this has implications well beyond athletic events. for more we are joined by kirk smith, lead author of the article, and professor of global environmental health at the university of california, berkeley. welcome e to democracy n now! professor smith, talk about what you have found. >> thank you for inviting me today. and sitting in berkeley, which is part of t the san francisiscy areaea and we often repeat what mark twain is often reported to say which is, the coldest winter i ever spent was a summer in san francisco. people who have been her know it is cool in the summer. this is going to be an advantage in the future as climate change p