The movement of the Earth around the Sun combined with the tilt of the Earth's axis causes weather, seasons and climate. The Sun causes weather patterns and the long-term average of weather patterns creates climatic zones around the world. The combined average regional climates create the Earth's climate. Changes in the Earth's revolution or axial tilt impact Earth's weather patterns and, when the deviation continues, Earth's climate.
Weather and Climate Definitions
Weather, in brief, consists of daily atmospheric conditions. From balmy breezes to fierce tornadoes, from hot and sunny to cold and cloudy and from fog to rain to snow: Weather consists of the day's combined atmospheric behavior.
Climate, on the other hand, consists of an average of weather patterns and conditions over a period of time (often 30 years or more). Climate includes both the average and the extreme weather conditions. Temperature, precipitation as rain and/or snow and wind patterns help define climatic zones.
Rotation and Revolution of Earth
The Earth rotates or spins around its axis once every 24 hours. The revolution of Earth around the Sun takes 365 days plus five hours. The Earth's path around the Sun isn't quite a circle, with the minimum distance about 91 million miles (146 million kilometers) and the maximum distance about 94.5 million miles (152 million kilometers). Interestingly, the Earth's closest approach to the Sun is during the northern hemisphere's winter.
Earth's Axial Tilt
The Earth's axis tilts approximately 23°27” from vertical. This axial tilt causes the Earth's seasonal differences and explains why the southern hemisphere experiences summer when the north hemisphere endures winter. This tilt also explains why the hours of day and night change with distance from the equator.
At the equator, the days remain essentially equal length throughout the year and the seasons don't change. The Sun's light and energy hit the equatorial area straight on throughout the year so the variation in temperature comes from wind and cloud cover.
As distance from the equator increases, the amount of energy and sunlight changes. In winter when the northern hemisphere is tilted away from the Sun, light and energy spreads out over the tilted surface. As the Earth's axis tilts away from the Sun, the light and energy decreases with distance from the equator. As the Earth revolves around the sun and the axial tilt brings the northern hemisphere into more direct line with the Sun's energy, the light and energy increase and the northern hemisphere enters summer.
One way to consider this energy disbursement is to think about toast and peanut butter. If at the equator the sunshine on one acre of land equals one tablespoon of peanut butter on a slice of toast, then that same tablespoon of peanut butter would be concentrated on a half piece of toast where the axial tilt aims the hemisphere toward the Sun, causing summer. On the other hand, in the areas tilted away from the Sun during winter, the tablespoon of peanut butter would be spread out over two or more pieces of toast.
Earth vs Regional Climate
In general, a discussion of climate refers to regional climates, or the climates in different areas of the Earth's surface. The Earth's climate, however, consists of the average of all the regional climates. Earth's climate then depends on energy received from the Sun and the energy trapped within Earth's systems.
Milankovitch Cycles and Earth's Climate
The Milankovitch cycles refers to three types of changes to the Earth's revolution around the Sun and rotation around its axis. Each of these changes impacts the Earth's climate.
The shape of the Earth's orbit changes from its current near-circular path to a more elliptical path and back to a near-circle. This change, called eccentricity, occurs over a 100,000-year cycle. When the Earth's orbit is more elliptical, the length of seasons changes and the Sun's energy becomes a greater influence than the axial tilt.
Obliquity means the tilt of the Earth's axis relative to the plane of the Earth's orbit around the Sun. The tilt ranges from 22.1 to 24.5 degrees. Greater tilt results in more extreme seasons while reduced tilt means milder, less extreme seasons. At this time the axial tilt is slowly decreasing. The change from 22.1 to 24.5 degrees takes approximately 41,000 years.
Precession refers to the wobble of the Earth's axis. Over the course of 26,000 years the wobble of the Earth's axis causes the North Star's position to form a circle in the sky. Precession combined with eccentricity impacts the differential severity of seasons between the northern and southern hemispheres.
Moon Rotation and Earth's Climate
Moon rotation around the Earth also influences the Earth's regional climates, impacting the Earth's overall climate. First, the Moon moderates precession, the Earth's axial wobble, meaning that the climates of the northern and southern hemispheres more closely resemble each other. Second, the Moon's gravitational pull creates bulges in the atmosphere similar to the tidal cycle of the ocean. These pressure changes, first recorded in 1847, influence rain patterns, one of the key components of regional climates.
- UCAR Center for Science Education: Climate
- National Snow and Ice Data Center: Climate vs Weather
- North Carolina Climate Office: Milankovitch Cycles
- Northern Arizona University: A Difference of Degrees: NAU Scientist Examines Earth’s Changing Tilt, its Effect on Antarctic Ice Cores and What that Says About Climate
- University of Washington: Moon’s Tidal Forces Affect Amount of Rainfall on Earth
- NASA: About the Moon - In Depth
- NASA Climate Kids: Which Pole is Colder?
- NASA: Planetary Fact Sheet - U.S. Units
- Hemera Technologies/AbleStock.com/Getty Images