Ask Dr. Global Change
Difference between climate and weather
Last updated 21 June 2005
Originally answered 18 April 2000
What is the difference between climate and weather?
According to the American Meteorological Society’s Glossary of Meteorology (second edition, 2000), climate is defined as “the slowly varying aspects of the atmosphere—hydrosphere—land surface system.”
This differs from the glossary’s definition of weather, which is “the state of the atmosphere, mainly with respect to its effects upon life and human activities.”
Climate is usually expressed by the statistical collection of weather conditions for a given region during a specific interval of time, usually several decades.
The average value of a meteorological element (e.g., temperature and precipitation) over a 30 year period is defined as a climatological normal. Climate normals help in describing the climate of a location and are used as a base to which observed conditions can be compared. The United Nation’s World Meteorological Organization (WMO) requires the calculation of climate normals every 30 years. The most recent such calculations cover the period of 1961-1990. However, many WMO members, including the United States, update their normals at the completion of each decade. Every ten years the U.S. National Climatic Data Center (NCDC) computes new thirty-year climate normals for selected temperature and precipitation elements for a large number of U.S. climate and weather stations. The most recently computed climate normals produced by NCDC cover the period of 1971-2000.
For a much more detailed discussion, see “What’s the Difference between Weather and Climate,” posted by NASA.