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close this bookBasic Concepts in Environment, Agriculture and Natural Resources Management: An Information Kit (IIRR, 1993, 151 p.)
close this folderGlobal warming and acid rain
View the documentClimate change and the greenhouse effect
View the documentHow deforestation contributes to the greenhouse effect
View the documentAcid rain

Climate change and the greenhouse effect

Climate change and the greenhouse effect

· Radiation from the sun passes through the earth's atmosphere to heat the earth.

· Heat radiating from the earth is partially trapped by the atmosphere, keeping the earth warm while some escape into space.

· Increasing concentrations of heat-trapping gases in the atmosphere occur because of human activities.

· The increase in these heat-trapping gases is likely to lead to global climate change which may include:

Temperature rise

· Sea level rise

· Extreme weather.

How deforestation contributes to the greenhouse effect

1. Forests store carbon. In the process of photosynthesis, trees absorb CO2 from the air (along with water, sunlight, nutrients and chlorophyll) and convert it to useable energy and wood. This wood is a sink or storage place for carbon.

Carbon dioxide

2. When forests are cleared and trees burned, carbon dioxide is released into the air.

releasing carbon dioxide into air

3. In addition, termites flourish in places where forests have been burned to make way for farms and cattle ranches. Methane-producing bacteria live in the guts of termites and help to break down the termites' woody food. Methane, released into the air, is a greenhouse gas.


Source: Outreach, Issue No. 56

4. Rice paddies on lands converted from forests produce methane gas which also contributes to the greenhouse effect.

Methane contributes to the greenhouse effect

Acid rain

Acid rain

Acid rain

Normally, rainwater is good for people, forests, crops, rivers and lakes. Rain water is slightly acidic with a pH of 5.6. Acid rain has been occurring for millions of years but with the industrial revolution of the 1 700s and the advent of coal burning, rainwater has become increasingly acidic.

Sulphur dioxide (SO2), Nitrogen dioxide (NO2) and even carbon dioxide (CO2) dissolve in rainwater to form dilute acids.

Acid rain harms trees and crops and upsets the balance of life in lakes and rivers. A lake that becomes too acidic looks crystal cleareven if it is lifeless. First, the aquatic plants are killed. The absence of these plants depletes oxygen sources for fish and amphibians. Acid rain does not kill the forest itself but makes it susceptible to insects and diseases.

Dry deposition: Sometimes, the oxides released into the air do not rise very far into the air, but return to the earth within a few hours and within 190 miles (300 km) or so from their source. These gases or particle fall directly onto the surface of plants, soils, water, etc. This is dry deposition.

Wet deposition: When SO2 and NO2 remain longer in the air, they react with moisture oxygen in the air to form dilute acids. Acid pollutants are carried by the wind for hundreds of miles often across national boundaries and fall to the earth with rain, snow, fog or mist. This is called wet deposition.

Dispersing the problem

Before the 1960's, smoke from industries polluted the nearby environment. In an attempt to improve the living conditions near the industrial plants, taller smokestacks were built. It was thought that the pollutants would be dispersed harmlessly into the atmosphere, but what they did was to create an international acid rain problem.

Dispersing the problem


The ozone layer rests 15 to 30 miles above the earth's surface. It absorbs and deflects 99 percent of the harmful UV rays from the sun. It shields the earth from harmful radiation.


Ozone layer shields the earth from harmful radiation

The ozone layer

The ozone acts as shield from harmful rays of the sun

CFC can destroy the shield

Ozone is a form of oxygen molecule combination with three atoms of oxygen.

The ozone layer rests 15 to 30 miles above the earth's surface. It absorbs and deflects 99 percent from the sun. It shields the earth from harmful radiation.

But the shield can be easily destroyed using CFC'sor chlorofluorocarbons.

CFC is a chemical invented during the 1 930s. It is used as a propellant for spray cans, perfumes and insecticides, air conditioning of cars, houses; and, refrigerator-freezing components use CFCs extensively. It is also used as a cleaning substance for electronics and as a solvent for dry cleaning.

CFC molecule

Other ozone destroyers include bromine containing haloes in fire extinguisher, methane and nitrous oxides and natural elements as volcanic ash and sea sprays.

How does a CFC molecule attack an ozone molecule?

The free chlorine atom goes to seek more ozones to destroy. One chlorine atom is said to be capable of doing permanent damage to 100,000 other ozones.

Cholrine atom

The damaged ozone molecule looks this way: like two idiots.

It is unable to perform any shield task at all and can never repair itself

Scientific researchers indicate that a hole as big as the antarctic continent has already been punched out in the ozone layer.

Hole in ozone layer

How do we repair the damage?
How do we prevent it from worsening?