Klaus Hasselmann (born 25 October 1931 in Hamburg) is a leading German oceanographer and climate modeller.
He is probably best known for developing the Hasselmann model of climate variability, where a system with a long memory (the ocean) integrates stochastic forcing, thereby transforming a white-noise signal into a red-noise one, thus explaining (without special assumptions) the ubiquitous red-noise signals seen in the climate.