U.S. acid rain regulations have worked. What's more, they didn't seem to get in the way of the country's longest economic expansion.
The bad news is that we really don't know what Eyjafjallajökull has in store. The last time it erupted was in the 19th century -- from December 1821 through January 1823. That's right: it coughed up its ash plumes for more than a year.