Sir Alexander Norman Halliday FRS (born 11 August 1952) is a British geochemist, an academic who is the Founding Dean of the Columbia Climate School, and Director of the Earth Institute at Columbia University. He joined the Earth Institute in April 2018, after spending more than a decade at the Department of Earth Sciences at the University of Oxford, during which time he was dean of science and engineering. He is also a Professor of Earth and Environmental Sciences at Columbia University.