In recent months, Americans have experienced numerous extreme weather-related events, including droughts, wildfires and heat waves. We 've witnessed the warmest spring since record-keeping began in 1895. Thirty-one states reached record-high temperatures. The period between July 2011 and June 2012 was the hottest 12 months on record. And last year 14 extreme weather-related events caused an incalculable loss of human life and cost the U.S. economy more than $55 billion. Understandably, many Americans are wondering if these events are manifestations of a longer-term shift in climate. At present we can not definitively link any single extreme event to climate change. But it is worthwhile to consider whether the apparent increase in some extreme events has roots in a larger, longer-term trend, since that would predict a continuation of these events in the future. That kind of understanding can have practical importance because it can inspire action to reduce economic losses and human suffering â $ often in relatively simple ways. If a region is likely to continue to get rainfall heavier than has historically occurred, for example, then it is sensible for city planners to consider installing larger-bore storm sewers when the time comes to replace aging infrastructure. The science in this area is getting stronger all the time. In one recently published study, six international