In an online PNAS article, the Spiegelman Lab reports on what happens when brown, white, and beige fat cells are exposed to a range of cold temperatures in vitro. They found that cooler temperatures can directly induce white and beige fat to activate a transcriptional program leading to thermogenesis, the generation of heat from chemical energy. Unlike thermogenesis induced by brown fat, this mechanism does not require norepinephrine, the primary chemical messenger of the sympathetic nervous system. See additional news coverage in Science and The Scientist.