“Hasselmann’s key insight was that climate scientists faced the same basic problem as communications engineers: how to detect a weak signal—the thing you’re interested in—amid lots of noise that you don’t care about. In climate science, the noise is caused by phenomena that are internal to the climate system, such as El Niño. The “signal” is something caused by things that are external to the Earth’s natural climate system: the Sun, volcanic dust, or man-made greenhouse gases.”