Wikibooks: Climate Change/Science/Sun-Earth System

• Format: Book
• Language: English
• Subjects: Antarc*; Antarctica
• Online Access: https://en.wikibooks.org/wiki/Climate_Change/Science/Sun-Earth_System

In [[Kepler}} showed that orbits are ellipses rather than perfect circles. Earth s orbit is slightly elliptical with an eccentricity of just 0.01671 ref eccen even though this value is small it has important consequences. The perihelion or smallest distance from the sun occurs during the northern hemisphere s winter and is about 1.47 \times 10^{11} m and aphelion the most distant point from the sun is during the northern hemisphere s summer and is about 152 \times 10^{11} m. This difference does not cause Earth s seasons but can influence the severity of seasons (discussed in the paleoclimate section) and does introduce small variations to the annual incoming solar radiation ( insolation ) as there are very slow variations in the eccentricity. A second important effect to consider is the tilt of Earth s spin axis with respect to the ecliptic plane which is basically the average plane of Earth s orbit around the sun. The angle between the spin axis and the perpendicular to the ecliptic plane is called Earth s obliquity and is currently about 23.4 degrees. This angle is the primary reason for seasons on Earth for as the planet traverses its orbit the amount of insolation at points on the surface slowly change with winter occurring when the pole faces away from the sun and summer when the pole faces toward the sun. Seasons are more extreme with larger obliquity and high latitudes (e.g. Antarctica) experience more extreme changes in insolation than the tropics leading to more pronounced season. Earth s obliquity slowly changes in time which has important consequences for very long term climate change. A third important part of the Earth sun geometry is called precession and is actually the combination of parameters. Precession is the slow variation of direction of the spin axis and is affected by both a turning of the spin axis and a slow change in the shape of Earth s orbit. For the contemporary climate the precession only matters because it determines the relative position of the poles to the sun during Earth s ...