Outline the causes of natural climate change including the theories of sunspots, volcanic eruptions and Milankovitch cycles
The Earth’s climate changes naturally for a number of reasons. Some of the causes are very long term, others much shorter term.
Long-term changes
The Earth’s orbit, tilt and ‘wobble’ are not constant; they change. As they change, so does the climate. The changes were discovered by a scientist called Milankovitch, hence them being called the Milankovitch Cycles.
Eccentricity
(Orbit change
Axial tilt
(Change in the axis)
Precession
(Axis wobble)
The Earth’s orbit changes from circular to elliptical.
The Earth is tilted on its axis. The degree of the tilt changes.
The Earth’s axis not only tilts, but also wobbles. So, the north pole points different ways.
100,000 year cycle
41,000 year cycle
26,000 year cycle
A more circular orbit will result in mild summers and mild winters. Winter snow will not melt, so glaciers form.
A smaller angle of tilt means milder summers and winters, so snow doesn’t melt and glaciers build up
Glaciers can build up in different hemispheres at different times.
Short-term changes
Two other natural events can change our climate; however, they are on a much smaller timescale.
- Volcanic activity – Ash and other volcanic material erupt into the atmosphere, which in turn blocks out the sun, meaning less insolation reaches the lower atmosphere, reducing temperatures. This can happen every few years.
- Sunspots – Spots, or dark patches, appear on the sun. When there are more sunspots, there is an increase in the surface temperature of the sun, which then increases the amount of insolation reaching the Earth. The change in the amount of sunspots changes over about an 11 year cycle.