The A-Z of Global Warming: Deforestation

Deforestation is basically the loss or destruction of forest habitat, primarily as a result of the action of human beings.

It is the single largest source of land- use greenhouse gas emissions, and accounts for around 18 -20% of global greenhouse gas emissions.

We know from a previous article, trees and vegetation act as sinks or stores for carbon dioxide, one of the most important greenhouse gases. Stored carbon taken out of the atmosphere by photosynthesis through decades of growth is released back into the atmosphere as vegetation and trees are cut down and burnt, or, as unburned organic matter slowly dies. This process contributes to atmospheric CO2 levels.

The Food and Agriculture Organisation of the United Nations (FAO) who are the leading source for information on the status of the worlds forests define forests as, "land with a tree canopy of greater than 10%, and an area of more than half a hectare". The organisation defines deforestation as, " the conversion of forest to another land use or long term reduction of the tree canopy cover below the minimum 10% threshold."

Land change and co2.

Land use changes are driven almost entirely by emissions caused through deforestation, which is highly concentrated in a few countries. Indonesia contributes approximately 30% of land use CO2 emissions with Brazil around 20%. It is estimated that about 80,000 acres or 32,000 hectares are being lost every day. This is the equivalent of about 117,000 km2, (45,173 sq miles) each year.

Total world rainforest cover is now about 6 million km2, (2,316,602 sq miles), which equates to about 5% of Earth's land surface. Only a few thousand years ago, rainforests covered about 12% of the worlds land surface, around 15.5 million km2, (6 million sq miles). A quick calculation reveals that if forest cover is being lost at the rate of 117,000 km2 a year, then it will only take in the region of 51 years for the world's rainforests to be destroyed! (6,000,000 divided by 117,000).

Destruction at this level would lead to the release of vast amounts of CO2 into the atmosphere, further thickening the CO2 "blanket" that surrounds our planet and no doubt lead to an increased warming of the atmosphere.

Between 2000 and 2006 Brazil lost nearly 150,000km2, (57,915 sq miles) of forest, an area the size of Greece, and since 1970 over 600,000 km2, (231,660 sq miles) has been destroyed.

It is now estimated that almost 20% of the Amazon has been destroyed, which is considerably alarming when one considers that the Amazon rainforest represents about 50% of the worlds tropical rainforests.

There are various causes for deforestation, and they include, Cattle ranching, Activities of farmers, fires, mining and road construction and of course logging and commercial agriculture.

It's not entirely fair to blame the developing nations for all the deforestation however. Whilst countries like Brazil and Indonesia may be the main culprits now, up until the early 20th Century emissions of CO2 through land use changes came from developed nations. It's a natural step for developing nations to clear forest-land for agriculture and habitation. The fact is that as developed nations have already deforested many areas long ago, there is more pressure on developing nations to preserve what is left. Of course population growth is another major factor which will be discussed in a later chapter. Another significant point is that trees in topical forests typically hold on average about 50% more carbon per hectare than trees outside the tropics. Therefore deforestation in these areas causes greater amounts of CO2 to be released into the atmosphere than deforestation outside of the tropics.

Future of the forests.

Remarkably when talking about land use change emissions, countries such as the USA, Europe and China were in the year 2000 net absorbers of CO2 as a result of their aforestation (planting new forests) and reforestation (re establishing old forest areas) programs. However, the planting of one tree does not offset the damage caused by the removal of another, as trees absorb CO2 very slowly. It could take 100 years for a growing tree to recover all the CO2 released when a mature tree is cut down!. For this reason, carbon offset programs which suggest planting a tress to offset co2 produced are pretty worthless, due to the time it would take for that tree to remove co2 from the atmosphere.

There is some good news however, as in 2006 the Brazilian government announced a sharp drop in deforestation. Loss for the year 2005/6 was 13,100 km2, (5,057 sq miles) down more than 40% from the year before. Its too early to say whether this is a declining trend, or just one good year out of the pervious eight where deforestation levels were all in excess of 16,000 km2, (6,177 sq miles).

As the worlds forests are being destroyed, huge amounts of CO2 are being released back into the atmosphere. The forests that were once able to absorb and store this potent greenhouse gas, will no longer be standing which will push CO2 levels up higher, thereby contributing to the warming of Earth's climate.


Copyright (c) 2008 Simon Rosser