Causes of Climate Change

The causes of climate change are many, and they fall into two broad groups: astronomical and terrestrial. Astronomical causes operate from outside the Earth, while terrestrial causes operate on or within the Earth itself. Understanding this division helps make sense of why climate has shifted so many times in the planet's history.

Astronomical Causes

These are causes linked to the Sun and the Earth's movements in space.

Sunspot activity. Sunspots are dark, cooler patches on the Sun's surface. Their numbers rise and fall in a cyclical manner. Some meteorologists hold that when sunspot numbers increase, the Earth experiences cooler and wetter weather along with greater storminess. Conversely, a decrease in sunspot numbers is associated with warm and drier conditions. However, these findings are not statistically significant — the link is suggestive, not firmly established.

Milankovitch oscillations. This is another astronomical theory, and it deals with cycles in three things: variations in the Earth's orbital characteristics around the Sun, the wobbling of the Earth on its axis, and changes in the Earth's axial tilt. All three alter the amount of insolation (incoming solar radiation) the Earth receives from the Sun. This change in insolation, in turn, can have a bearing on the climate. So even small shifts in how the Earth moves and tilts can add up to significant climatic effects over long periods.

Terrestrial Causes

These are causes that originate on or within the Earth.

Volcanism. Volcanic eruptions throw up large quantities of aerosols into the atmosphere. These aerosols remain suspended in the atmosphere for a considerable period of time, and while there, they reduce the amount of the Sun's radiation that reaches the Earth's surface. After the recent eruptions of Mount Pinatubo and El Chichón, the average temperature of the Earth fell to some extent for some years. This shows how a single major eruption can cool the planet temporarily. …