(Encore episode.) Archival records may help researchers figure out how fast the sea level is rising in certain places. Millions of people in coastal cities are vulnerable to rising sea levels and knowing exactly how fast the water is rising is really important. But it's a tough scientific question. NPR climate correspondent Lauren Sommer explains how scientists are looking to historical records to help get at the answer. If you'd like to help transcribe old tidal data, you can get started here.For more of Lauren's reporting, follow her on Twitter @lesommer. Email us at ShortWave@npr.org.