Factors Affecting Past Climates. I. The Earth\'s Climate has changed many times, due to natural causes. **There have been at least 4 Ice Ages in the last 3 million years - with only a 5oC cooler difference!.
**There have been at least 4 Ice Ages in the last 3 million years
- with only a 5oC cooler difference!
Just 18,000 years ago, the Earth was in an ice age where continental glaciers reached as far south as the Ohio River Valley over North America.
(A) Variations in the Earth\'s Orbit (tilt or shape) - cycles from 20,000 to 100,000 yrs.
Plate tectonics and drift concentrated continents at higher latitudes allowed for more ice cover, which reflected more sunlight and created a positive feedback to cause greater cooling.
Periods of mountain building increase snow-covered high elevation areas producing a similar snow-albedo positive feedback.
The position of continents, mountains, and oceans create complex changes in atmospheric (and oceanic circulation).
In 1915, Meteorologist Alfred Wegener (1880-1930) hypothesized the movement of continents based on fossil evidence. Some evidence he used was the presence of coal in Antarctica, evidence for glaciation in Africa, and similar fossils in South America and Africa.
Geologists rejected Wegener\'s theory, believing that the Earth\'s crust is too rigid to change positions. The theory of continental drift reemerged around 1960 based on paleomagnetic evidence of sea-floor spreading.
Variations in Solar Radiation
Earth-Sun Geometry (Milankovitch cycles)
Atmospheric Dust and Volcanoes
Distribution of ContinentsPlate TectonicsMountain Building
Positive vs Negative Feedbacks