Deforestation

Before agriculture, forest covered 57 million km² of the earth (Malhi et al 2002), however, as a result of domestication much of this forest cover has been lost.  As domestication became more wide spread and intensive, it was necessary to clear land to create space for grazing and crops.  

Deforestation has an impact on global climate through increasing the release of carbon dioxide into the atmosphere.  Clearing often occurs through burning the forests which its self releases high concentrations of carbon dioxide into the atmosphere, but also the vegetation and the soil store large amounts of carbon which is subsequently released into the atmosphere when forests are burnt or logged.  Crops or grasses in grazing areas do not store as much carbon as large forested areas, meaning there is a higher concentration of carbon in the atmosphere.  

Burning of forest from charcoal records can be seen around the beginning of domestication 8000 years ago, and forest clearances seems to accompany the spread of agriculture.  It seems that most temperate forests, for example in Europe and China, have been cleared progressively since the beginning of domestication, a very small amount survived to the industrial era (Malhi et al, 2002).  However, until 1700 only about 7% of global forests had been lost (Goldewijk, 2001).  This has significantly increased in recent years and deforestation has contributed to 45% of the increase in atmospheric carbon dioxide since 1850 (Malhi et al, 2002).  This is as a result of more widespread deforestation and deforestation of more densely forested tropical areas which are thought to be ‘carbon sinks’.  

Carbon sinks are forests which are thought to be fertilised by the recent increase in atmospheric carbon dioxide, leading to increased growth rates meaning the forests store more carbon so there is less in the atmosphere. The Amazon rainforest is an example of this and it is thought to be actually slowing the anthropogenic effect, however if these forests are deforested they then become a huge source of carbon (Laurance 1998).  They are very resilient if they remain intact, however many, like the Amazon are being deforested for agricultural purposes, for example by 2001 837000 km² was cleared for cattle ranching and soya bean production (Malhi et al 2008).  Clearing leads to fragmentation of the environment, limiting regrowth.  Much of the tropical forests in southeast Asia have been lost, the map below shows loss in Borneo, and projections for the future.  

It is likely that if large areas of these tropical forests are deforested, they will become large sources of carbon which will increase atmospheric concentration.  Therefore policies are continually being put in place to limit deforestation and protect forests.  There are many campaigns, such as Green Peace, their video below is useful for seeing the effects of deforestation in the Amazon rainforest.