Satellites seem like an obvious technological solution to the considerable challenge of tracking changes in Earth’s climate. But Earth-observing ain’t easy. A single instrument can zoom over the locations of thousands of stationary thermometers—but that puts thousands of eggs in one instrumental basket. Measuring temperatures from space takes a lot more than some mercury in a tube, and you can’t fix your instrument if something goes wrong.

Illustrating that fact is a new update to one of the major satellite temperature datasets, which ends up changing the recent part of the record in a subtle but significant way.