Ask Dr. Global Change
Climate and Earth's Rotation
Last updated 21 June 2005
Originally answered 11 December 2001
What would happen to climate patterns in the world if the Earth’s rotation would go in the opposite direction?
Although extremely unlikely to ever occur, the hypothetical situation of the Earth rotating in the opposite direction poses an interesting question and prompts a look at how this feature of our planet affects climate.
The rotation of the Earth, which is counterclockwise as viewed from above the North Pole, has many effects on Earth’s weather and climate.
Though not directly related to weather or climate, one of the most obvious results of a reversal in the Earth’s rotation is that the Sun would rise in the west and set in the east.
The Coriolis effect, which results from the Earth’s rotation, plays an important role in large-scale circulation of the atmosphere. As viewed by an observer on Earth, air appears to be deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. This results in areas of low pressure rotating counterclockwise in the Northern Hemisphere and clockwise in the Southern hemisphere, with the opposite being true for areas of high pressure. If the Earth’s rotation were to suddenly reverse itself, these patterns would also be reversed. The westerlies would become easterlies and the northeast trades would blow from the northwest. This would
Changes in the Earth’s rotation would have an effect on ocean currents, which can influence local climates. The El Niño and La Niña phenomena that affect global climate patterns on a periodic basis.
One large component of a location’s climate that would not likely be affected would be the effect of seasons, which are more dependent on the tilt of the Earth’s axis than they are on the Earth’s rotation.
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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.