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What is the "Greenhouse Effect"?The trapping and build-up of heat in the lower atmosphere near the planet's surface. Some of the heat flowing back towards space from the Earth's surface is absorbed by water vapour, carbon dioxide (CO2), methane (CH4), and other gases in the atmosphere. If the atmospheric concentrations of these gases rise, then theory predicts that the average temperature of the lower atmosphere will gradually increase. The greenhouse effect in part explains the temperature differences of Mars, Venus and Earth.
What is the "enhanced" greenhouse effect?A increase in the natural greenhouse effect, brought about by human activities, whereby greenhouse gases such as carbon dioxide (CO2), methane (CH4), chlorofluorocarbons and nitrous oxide (N20) are being released into the atmosphere at a far greater rate than would occur through natural processes and thus their concentration in the atmosphere is increasing.
What is a "carbon sink"?The term "sink" is commonly used to describe the carbon (C) taken from the atmosphere by plants and stored in living and dead organic matter both above and below ground in land-based (or terrestrial) ecosystems. Forests remove carbon dioxide (CO2) from the atmosphere and sink carbon (C) in plant material and soil. This natural process is part of the carbon cycle and is known as sequestration. Half a tree's mass is carbon, so large amounts of carbon are stored in forests and they are the largest carbon store of terrestrial carbon. Depending upon the particular forest, the amount of carbon stored in it may be; increasing - making the forest a carbon sink, decreasing - a carbon source, or in carbon balance - a carbon store. Other ecosystems such as savannas and woodlands are also significant sinks. In most ecosystems, the majority of the carbon is stored belowground, either as roots and decaying biomass or as organic carbon in the soil. Forests can absorb CO2 from the atmosphere and thereby assist us temporarily to stabilise greenhouse gases in the atmosphere. However, half of the world's forests have already been cleared and those that remain have largely been degraded. We have therefore reduced the capacity of the world's forests to slow climate change. Currently, the total carbon stored in global terrestrial pools is increasing as a result of CO2 fertilisation, nitrogen deposition and warming. However, much of the increase is due to regrowth of forests and other woody vegetation on abandoned cropland and pastures. The increase in the terrestrial carbon pool is likely to slow mid-century or during the 22nd century.
Why are carbon sinks important?The concentration of carbon dioxide (CO2) in the atmosphere is increasing. Humans are continuing to release large amounts of CO2, largely from burning fossil fuels (oil, gas and coal) and from activities such as clearing forests. Each year, human activities are thought to add an extra 7 billion tonnes of CO2 to the atmosphere. Because CO2 traps heat in the atmosphere, increasing concentrations of CO2 is leading to global climate change. Many scientists predict that climate change will result in more extreme weather patterns - more cyclones, floods and droughts. With such changes in our climate, rising sea levels will threaten coastal environments, it will be harder to grow food successfully, and the rate of species extinction will increase. To reduce the impacts of climate change, it is necessary to stabilise atmospheric CO2 concentrations. In the 250 years since the industrial revolution, the amount of CO2 in the atmosphere has increased by 30%. To stabilise CO2 at current levels, we need to reduce emissions by 50% - 70% now. To stabilise CO2 at twice pre-industrial levels, emissions need to be reduced by 30% now. Forest carbon sinks can help us to do this through the natural absorption and storage of carbon dioxide. An international agreement, the UN Framework Convention on Climate Change (UNFCCC) was ratified in 1994. The UNFCCC aims to stabilise atmospheric greenhouse gas concentrations to prevent human induced climate change. The Kyoto Protocol, is a protocol of the UNFCCC. The Kyoto Protocol pursues action to combat global warming by managing greenhouse gas sources and sinks. It has not been ratified, and decisions about how it will be implemented are still being negotiated. Under the Kyoto Protocol, developed countries have set emissions reduction targets that are an average of 5% below 1990 levels. There are a number of mechanisms in the Protocol, including carbon trading, that can help some countries reach their emissions reduction target.
How can sinks help combat global warming?As part of what is called the 'global carbon cycle', carbon is exchanged naturally between the land, the atmosphere and the oceans. Forests sinks play a very important role in this natural ecological cycle and can combat global warming by removing CO2 from the atmosphere and storing the carbon. But, forest sinks can only offset a relatively small proportion of total greenhouse gas emissions. We cannot combat global warming with forest sinks alone. We also must reduce our industrial emissions. As a matter of necessity, we fundamentally need to change the way that we choose to produce and use energy as well as massively reduce our levels of fossil fuel consumption. These changes will be difficult and will take many years. Forest sinks start working immediately, providing the time needed for slower industrial change. We need to use this time effectively - industrial change needs to start now.
Should sinks be used to help combat global warming?Forest sinks are important to buy us time for technological and social change, but there is a limit to the amount of carbon that can be stored in forests. Forests alone cannot solve the problem of climate change. Forest sinks are not an alternative to reducing emissions, they are only part of the solution. Australians produce on average per person, more than four times the world average for greenhouse gas emissions. Our per capita greenhouse gas emissions are among the highest in the world so it is essential that we reduce industrial greenhouse gas emissions.Reduction in fossil fuel use can by achieved by:
The most permanent carbon storage is within fossil fuels that remain unextracted and unburnt in the ground. In contrast, the security of carbon stored in forests is uncertain. Carbon may be released easily and accidentally from forests back to the atmosphere, for example, by logging or fire.
FAQ acknowledgements
©
CRC for GA 2001-2003 |
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