Causes of Climate Change
The Earth’s climate is not constant. It is known to have changed in the past (e.g. Ice Age) and will continue to change in the future as well. Climate change can be caused by a variety of factors which are called climate forcings that can be either internal or external. Internal climate forcings encompass processes that are directly related to climate such as ocean circulation, while external climate forcings refer to external factors that can influence the Earth’s climate such as solar output. Climate Forcings
- Milankovitch cycles
Milankovitch cycles (named after their discoverer, the Serbian mathematician, astronomer and geophysicist Milutin Milanković) refer to climate change that is caused by variations in the Earth’s orbit, more specifically eccentricity, changes in the tilt angle of the axis of rotation and the precession of the axis. The so-called Milankovitch cycles have been shown to have a major influence on the Earth’s climate and explain the ice ages in the planet’s past. But they also indicate that the Earth’s climate can be expected to change in the future.
- Solar output
The amount of energy the Earth receives from the Sun changes through time. For example, the Sun emitted only about 70% of today’s power when the Earth was formed 4 billions years ago. The energy that is emitted from the Sun increased dramatically over the next 4 billions years and as a result, our planet got warmer. But the Sun has also been shown to have variations in intensity of energy output which have a major influence on the Earth’s climate. One of such variations of solar output is thought to be responsible for the Little Ice Age (between 1550 and 1850).
- Volcanic eruptions
Volcanic eruptions are accompanied by release of huge amounts of gases into the atmosphere. If large enough, volcanic eruptions can cause significant climate change because they can interfere with the solar energy transmission to the Earth’s surface and change ocean circulation. For example, volcanic eruption in the Siberian Traps that happened over 250 millions years ago is thought to be responsible for the Permian-Triassic extinction which killed 90% of species.
- Motion of tectonic plates
These do not only trigger potentially devastating earthquakes but they can also have a major influence on the climate by changing topography in land and oceans. In the latter case, they can alter the patterns of ocean circulation which in turn can dramatically change the climate patterns.
- Human activities
Most scientists agree that the abnormalities in the Earth’s climate after the mid-19th century and especially after the mid-20th century can be attributed to human activities, in the first place fossil fuel burning and deforestation. Fossil fuel burning releases large amounts of CO2 and other gases which have been shown to have a greenhouse effect. Deforestation, on the other hand, enhances the greenhouse effect because fewer trees equals fewer CO2 absorption. The forests play an important role in climate because the trees absorb huge amounts of CO2 and other greenhouse gases while releasing pure oxygen.