Longterm climate change Shortterm climate variability Longterm climate

Long-term climate change & Short-term climate variability

Long-term climate change

Solar radiation Most important forcing mechanism for climate Amount of solar radiation that the Earth surface (or any part thereof) receives is slowly but continuously changing Changes are related to variations in the orbit of the Earth about the Sun As a result, climate will also inevitably change Climate change is perfectly normal

Milankovitch theory Proposed in 1920 by Milutin Milankovitch to explain the cycle of glacial & interglacial periods (widely accepted today) 3 important orbital parameters: – eccentricity of Earth’s orbit – tilt of Earth’s axis of rotation – precession of Earth’s orbit In combination, these influence the amount & distribution of solar radiation reaching the Earth, which changes with both latitude & season Each parameter has a unique periodicity

Eccentricity of Earth’s orbit Present orbit Orbit 50, 000 years ago This graph shows the variation in the eccentricity of the Earth's orbit over the last 750, 000 years. The primary periodicity is approximately 100, 000 years. The blue line traces the eccentricity with respect to time. The orange line shows today's value for comparison. Horel and Geisler, p. 78 http: //www. museum. state. il. us/exhibits/ice_ages/

Tilt of Earth’s axis Tilt = 0 Tilt = 23. 5 This graph shows the variation in the tilt of the Earth's axis over the last 750, 000 years. The tilt varies from 21. 6 o to 24. 5 o, today’s tilt is 23. 5 o. The primary periodicity is approximately 41, 000 years. The blue line traces the tilt with respect to time. The orange line shows today's value for comparison. Horel and Geisler, p. 79 http: //www. museum. state. il. us/exhibits/ice_ages/

Precession of Earth’s orbit At present, the time of the perihelion occurs near the winter solstice. In 11, 500 years, the time of the perihelion will occur near the summer solstice. Horel and Geisler, p. 80

Precession of Earth’s orbit This graph shows the precession of the equinox over the last 750, 000 years. The combined effect of changing aphelion and perihelion and equinoxes has periodicity of about 22, 000 years. The precession is expressed as the longitude of the perihelion from the vernal equinox. The blue line traces the precession with respect to time; the orange line shows today's value for comparison. http: //www. museum. state. il. us/exhibits/ice_ages/

Combination of periodicities Sum Precession Tilt Eccentricity Horel and Geisler, p. 80

Vostok ice core, Antarctica