For the 19th century provisional governor of Virginia see Gilbert Carlton Walker

Sir Gilbert Walker was an English physicist and statistician of the 20th century. He is best known for his groundbreaking description of the Southern Oscillation, a major phenomenon of global climate, and for greatly advancing the study of climate in general.

A professor of electrodynamics at Cambridge University, Walker joined the British Foreign Service in 1903 and was stationed in India, where he rose to head the British meteorological service. While in India, he drawn to study the characteristics of the Indian Ocean monsoon, the failure of whose rains had brought severe famine to the country in 1899. Analyzing vast amounts of weather data from India and lands beyond, over the next fifteen years he published the first descriptions of the great seesaw oscillation of atmospheric pressure between the Indian and Pacific Ocean, and its correlation to temperature and rainfall patterns across much of the Earth's tropical regions, including India.

Walker continued his studies of yearly weather and climate change after his retirement from India and acceptance of a professorship in meteorology at Imperial College. He had only mixed success in his original goal, the prediction of monsoonal failures; however, his theories and broad body of supporting research represented an invaluable step forward, allowing his successors in climate study to move beyond local observation and forecasting toward comprehensive models of climate worldwide.