Significant reductions in surface and atmospheric temperatures on Earth result in long-term periods of glaciation, which is known as an “ice age”. These periods are characterized by the growth and expansion of ice sheets across the Earth’s surface, which occurs every few million years.
During an ice age, there are significant temperature differences between the equator and the poles, and temperatures at deep-sea levels also tend to drop. This allows for large glaciers (comparable to continents) to expand, covering much of the surface area of the planet.
BODY PARAGRAPH-2: CAUSES OF ICE AGE
- 1. Earth’s Orbit: Since earth’s orbit around the Sun is subject to cyclic variations over time (Milankovitch cycles), redistribution of the sunlight received by the Earth occurs. The timing of glacial and interglacial periods are so close to changes in Milankovic orbital forcing periods that it is the most widely accepted explanation for the last ice age.
- 2. Tectonic Plates: The geological record shows an apparent correlation between the onset of ice ages and the positions of the Earth’s continents. During these periods, they were in positions which disrupted or blocked the flow of warm water to the poles, thus allowing ice sheets to form. This in turn increased the Earth’s albedo, which reduces the amount of solar energy absorbed by the Earth’s atmosphere and crust.
- 3. It is also believed that the Himalayan mountain chain which formed 70 million years ago has played a major role in the most recent ice age. By increasing the Earth’s total rainfall, it has also increased the rate at which CO2 has been removed from the atmosphere (thereby decreasing the greenhouse effect). Its existence has also paralleled the long-term decrease in Earth’s average temperature over the past 40 million years.
- 4. Atmospheric Composition: According to the “Snowball Earth” hypothesis – in which ice completely or very nearly covered the planet at least once in the past – the ice age of the late Proterozoic was ended by an increase in CO2 levels in the atmosphere, which was attributed to volcanic eruptions.
By definition we are still in the last great ice age – which began during the late Pliocene epoch (ca. 2.58 million years ago) – and are currently in an interglacial period, characterized by the retreat of glaciers. The exact role played by all the mechanisms that ice ages are attributed to – i.e. orbital forcing, solar forcing, geological and volcanic activity – are not yet entirely understood. However, given the role of carbon dioxide and other greenhouse gas emissions, there has been a great deal of concern in recent decades what long-term effects human activity will have on the planet.