11. Deforestation and climate change

How do human activities lead to increase in greenhouse gases and cause climate change?

Types of human activities that contribute to increased greenhouse gases in recent times:

• • deforestation and

  • land use changes.

View the video on the state of the world’s forest from 2:30 to 3:45 @ http://www.wri.org/project/global-forest-watch

Watch the video to find out more on how deforestation results in climate change.

Log on to Google Earth KMZ Disappearing Forests of the World by David Tryse.

Instructions to access Google Earth:

a. Download Google Earth onto PCs.

b. Open Google and look for the ‘Layers’ tap on the left hand side of the screen.

c. Click on the ‘Earth Gallery’ button.

d. In the ‘Search Earth Gallery’ box, type in ‘Disappearing Forests’

e. Select the title ‘Disappearing Forests’ by David Tryse by clicking on ‘Open in Google Earth’.

f. Check that 3-D on deforestation rate (area/land) is switched on by making sure that the ‘Pie Chart only (no 3D)’ is not selected

Let's analyse how deforestation contribute to climate change.

• Describe the relationship between deforestation and the emission of CO2, using data from resource.

• What does this data tell us about the impact of deforestation on a global scale?

• There is a direct relationship between deforestation and the emission of CO2. More CO2 is emitted when more deforestation occurs. This is seen e.g., in 1995 when deforestation was at its peak of over 2.5mil hectares and the CO2 emission highest estimate was nearly 1200 million tonnes. Conversely, when deforestation was at its lowest, as in 1991, CO2 emissions were around a much lower amount of 500 million tonnes.

• The data shows that deforestation is a human activity that leads to the rise of CO2 in the atmosphere.

• CO2 is released by decaying vegetation.

• In addition, most forest trees are cleared through burning. CO2 is a by-product of burning which is released into the atmosphere, only to remain because of the absence of vegetation to recycle the greenhouse gas.

• The hydrological cycle has an important ecological function. The trees absorb carbon dioxide in the cycle of processes. The hydrological cycle is the continuous movement of water between the earth and the atmosphere. Water reaches land as precipitation such as rain and snow. Then the water evaporates, condenses in the atmosphere to form clouds, and falls to the earth again as precipitation, continuing the cycle. During these processes, trees absorb CO2 and release O2 into the atmosphere. When water falls to the ground it can collect on the land becoming surface runoff, lakes, or infiltrates into the ground to become groundwater. Forest vegetation intercept rainwater either using it or releasing it to the atmosphere through evapo-transpiration.

• With increased temperatures, there will be more condensation, leading to more precipitation in over certain areas.

• With increased temperatures, there will be more evaporation leading to more arid conditions and desertification, with more droughts and prolonged drought conditions experienced in some areas.

Large-scale deforestation reduces the amount of vegetation to absorb carbon dioxide, thus more carbon dioxide in the atmosphere to trap heat and cause an increase in global temperatures. Forest fires also contribute to the emission of carbon dioxide in the atmosphere.

Soil is one of the largest sources of carbon in the world. Carbon in the soil accumulates through the decay of organic matter such as dead leaves and animals. Deforestation exposes soil to sunlight. This increases soil temperature and the rate of carbon oxidation in the soil. Carbon oxidation is a process by which carbon in the soil reacts with oxygen in the atmosphere to produce carbon dioxide. As such, deforestation increases the rate in which carbon dioxide is released from the soil into the atmosphere.

The greatest overall loss of forests occurs in South America. Southeast Asia experiences the second highest rate of deforestation. Great losses in forests also occur in Australia and Africa. For many of these places, the need for development is the cause of forest clearance. Such development includes agricultural and commercial activities such as cattle ranching, soybean production, commercial logging and mining.