Study Note - Climate Change – Processes of Internal Forcing

Internal mechanisms can generate climate, and these range from the formation of mountain ranges over many years to the rapid deforestation of a rainforest. Changes in orography (the relief of the land) and ocean shape do have an effect on the climate, but take a lot longer to come into effect. Changes in surface features may have drastic effects on climate over shorter periods of time.

Deforestation is a clearly visible case of a change in surface properties which, by changing surface albedo (the reflectivity of a surface) and heat budget, could certainly affect climate.

The removal of temperate forests in Europe and tropical forests in South America and East Asia have the potential to modify climate, and some models predict that a change in Brazil from rain forest to savannah-type environment could lead to a decrease in evapotranspiration of up to 40% . This would also lead to an increase in surface run-off and an increase in soil temperature.

Another example of anthropomorphic internal forcing of the climate, although this is a more localised case, is when large amounts of smoke were released from the Kuwaiti oilfield fires in the First Gulf War. None of the smoke was able to penetrate the stratosphere, but there were localised climatic effects.

Non-human related, short-term activities also cause internal forcing of climate change, such as volcanic eruptions. The eruption of Mount Pinatubo in the Philippines in June, 1991 led to a brief reduction in global mean temperatures, as large volcanic eruptions send dust into the stratosphere, sometimes spreading the dust and particulate matter globally.

Major eruptions in the late 18th and early 19th Centuries are usually thought to be responsible for the oddly-coloured skies in British landscape paintings of the time, which could be evidence of how far the volcanic dust can travel when it is caught up in the stratosphere.