The temperature difference from the pole to the equator depends on the Sun's energy and the energy retained in Earth's systems. There have been times when the Earth didn't have polar ice caps or deserts and there have been times when ice buried much of the Earth's surface. Even small changes in Earth's energy balance impact the temperature at the equator, the poles and every place in between.
The equator receives the most direct sunlight and therefore the most solar energy. In general, the climate zone between 15 degrees north and 15 degrees south (15°N and 15°S) latitude has average temperatures above 64°F (18°C). The day-night temperature difference generally is greater than the temperature difference between the equator's warmest and coldest months. Elevation and weather patterns like thunderstorms influence the local equator temperatures as well.
During summer, the temperature at the north pole averages 32°F (0°C) while the temperature at the south pole averages −18°F (−28.2°C). During winter, the temperature at the north pole averages −40°F (−40°C) but the temperature at the south pole averages −76°F (−60°C). Geography controls the temperature difference between the north and south poles.
The north pole is located in ocean while the south pole lies on a continental mass surrounded by ocean. The sea water below the Arctic ice cap is slightly warmer than the ice and warms the air above. The land mass of Antarctica, however, reduces the influence of the ocean. The average elevation of Antarctica, about 7,500 feet (2.3 kilometers), also lowers the temperature at the south pole.
Earth's Curvature and Temperature
The curvature of the Earth causes the Sun's energy to spread out over larger areas with increasing latitude. The greater the land area the energy spreads across, the lower the energy per unit area. Ultimately the temperature in an area depends on the amount of the Sun's energy reaching the surface in that area. The amount of solar energy in a given area is greater at the equator than in an equal area at the poles, which is why the equator temperature is warmer than the polar temperatures.
Axial Tilt and Sun Energy
The Earth's axis tilts approximately 23.5° from vertical relative to the plane of the Earth's orbit around the sun. This axial tilt means that during the Earth's journey around the sun the poles receive varying amounts of sunlight. The equator, however, receives relatively consistent sunlight all year. The consistency of energy means the equator's temperature stays relatively constant all year.
The polar regions, on the other hand, receive less of the Sun's energy and only receive that energy for part of the year. At latitudes higher than 60°N and 60°S the Sun's energy spreads out over large areas due to the Earth's curvature and axial tilt. Less energy per unit area means lower overall temperatures. The axial tilt means that each pole receives constant sunlight during its summer when the pole is pointed toward the Sun. During winter, however, the pole receives no sunlight at all because the pole is tilted away from the Sun.
Atmosphere, Ocean and Temperature
While the difference between the average equator temperature and the poles' temperatures may seem extreme, the difference would be much greater without Earth's atmosphere. The equator would become very hot and the poles become even colder. Solar energy drives equator weather patterns, absorbing heat into thunderstorms and transferring heat from the atmosphere to the ocean as rain.
Convection currents in the atmosphere cause wind patterns that move heat from the equator toward the poles. Ocean currents warmed by the Sun's energy carry heat from the equator toward the poles as well. Evaporation of surface water, rain and other precipitation, wind and ocean currents move warm air toward the poles and bring cold air toward the equator.
- National Earth Science Teachers Association: The Earth’s Rotation
- National Earth Science Teachers Association: Earth’s Tilt Is the Reason for the Seasons
- UCAR Center for Science Education: Climate
- National Snow & Ice Data Center: Climate vs Weather
- NOAA Climate.gov: Teaching Essential Principle One - The Sun is the Primary Source of Energy for Earth's Climate System
- NASA Climate Kids: Which Pole is Colder?
- National Geographic: Climate
- NASA Earth Observatory: Climate and Earth's Energy Budget
- Encyclopaedia Britannica: Köppen Climate Classification
- atlas globe image by Jorge Casais from Fotolia.com