The recent heat wave baking much of the country has prompted many people to ask: Is this due to climate change? "This is always the million-dollar question, but unfortunately, there's no definitive way to answer it," says Steve Vavrus, a senior scientist in the Nelson Institute Center for Climatic Research at the University of Wisconsin-Madison. "We've experienced extreme heat, drought, floods, wildfires and windstorms throughout history, so in a sense this is nothing unusual. We need time to assess whether this year's set of extreme weather events falls outside of normal variations. The list of unusual conditions over the past year is long. According to the National Oceanic and Atmospheric Administration (NOAA), last winter was the fourth-warmest on record in the United States; spring was the warmest since recordkeeping began in 1895; and April marked the end of the warmest 12-month period in U.S. history.