Scientists say Earth's climate has warmed 1.4 degrees Fahrenheit in the last century. But Ken Miller of Glen Burnie asks, "What baseline for calibration was used then and now? I am sure they are different. How can we believe this is right?" Climatologist Robert Henson says three major groups here and abroad track temperatures in different ways, using the longest, most reliable data sets each can find. They differ on what the global temperature is, but they agree closely on the increase. That's good evidence they're right.