Greece's huge forest fires have been blamed by some on global warming, but satellite images of smoke plumes drifting as far as Africa prompt the question: are forests a major source of greenhouse gas?
Usually it is cars, factories and power stations that are most often mentioned as sources of carbon dioxide (CO2), a gas which traps heat in the atmosphere. Trees, considered the "lungs of the planet", soak the gas up. But what if they burn?
"Global emissions from deforestation and the degradation of forests are the second single source after coal," said Stefan Singer of WWF (the World Wildlife Fund).
Every year 13 million hectares of the world's forests disappear -- an area the size of Greece -- according to the United Nations Food and Agriculture Organisation which says deforestation accounts for 18 percent of CO2 emissions.
Although paling in significance next to deforestation in the Amazon, Congo and Indonesia, forest fires in the Mediterranean might also be a net source of emissions, experts said.
Trees absorb carbon dioxide as they grow and climatologists see forests as carbon "sinks" -- places where large amounts of that element are stored. When they burn, whether in forest fires or as logs in a stove, it is released.
In the atmosphere, CO2 is the main gas which contributes to the greenhouse effect -- trapping the earth's heat which would otherwise be radiated into space.
The latest U.N. report on global warming says temperatures will rise by a best estimate of 1.8 to 4.0 Celsius (3 to 7 Fahrenheit) this century and sea levels will rise by between 18 and 59 centimetres.
CAUSE AND EFFECT
