Following a plateau in the early 2000s, global concentrations of the powerful greenhouse gas methane have hit new highs in recent years. Chemical fingerprint tests seem to rule out a major role for fossil fuels. With more than half a dozen possible natural and human sources, how will  scientists figure out where it's coming from? 

If you had to pick your Fourth of July picnic location based solely on past weather, where does the climate record say you'll have the least chance of rain? Our interactive map shows historic odds of rain on your parade.