Enhanced greenhouse effect a hot international topic
This topic is sponsored by BHP.
The Kyoto Protocol put the enhanced greenhouse effect in the spotlight. But what is the enhanced greenhouse effect and what are we doing about it?.
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Without the greenhouse effect we would be living in a very chilly place the world's average temperature would be minus 19°C, instead of the 14°C we are used to. So what is the greenhouse effect and how does it make Earth around 33°C warmer?
The natural greenhouse effect
The natural greenhouse effect is a phenomenon created by the heat energy radiated by the sun and greenhouse gases normally present in the atmosphere. In simple terms, sunlight passes through the atmosphere, warming the Earth. In turn, the Earth radiates this energy back towards space. As it passes through the atmosphere, greenhouse gases (water vapour, carbon dioxide, methane and nitrous oxide) absorb part of the energy, while the remainder escapes into space. This means that some of the sun's energy becomes trapped thus making the lower part of the atmosphere, and Earth, warmer.
Image: IPCC 2007
Energy in balance
If the atmosphere accumulated all the trapped heat, then the Earth's temperature would just rise and rise, but it doesn't. The temperature only rises until the amount of infrared or long wave radiation leaving the Earth balances the amount of energy coming in from the sun. As long as the amount of greenhouse gases in the air stays the same, and as long as the amount of heat arriving from the sun is constant, an equilibrium is established. This is a steady state where as much energy is lost to space as is gained from the sun. In equilibrium, the natural greenhouse effect maintains the average temperature of Earth at around 14°C.
The atmosphere is changing
The Earth's atmosphere is made up of 78 per cent nitrogen and 21 per cent oxygen. Only about 1 per cent is made up of natural greenhouse gases, but this comparatively small amount of gas makes a big difference. Before the Industrial Revolution (which started in England about 200 years ago) the mix of gases that made up the atmosphere was relatively constant. The Industrial Revolution brought new industrial processes, more extensive agriculture, and a rapid increase in the world's population. This rapid increase in human activity meant that more of the gases which cause the greenhouse effect were released into the atmosphere. We know this because of measurements made over the last 35 years and the analysis of air bubbles trapped in ancient ice. There is now clear evidence that levels of carbon dioxide, methane, nitrous oxide and halocarbons are increasing (Box 1: Greenhouse gases).
The enhanced greenhouse effect and climate change
Many scientists think that the increasing concentrations of these greenhouse gases has led to an increase in the world's average temperature. This is called the enhanced greenhouse effect.
While scientists agree that the levels of greenhouse gases are rising, there is less certainty about what the precise effects of this will be. To help them understand these effects, scientists use mathematical models (Box 2: What is modelling?). These models take account of many processes that together determine the behaviour of the atmosphere (eg, temperature, humidity, wind speed and atmospheric pressure). Many researchers are predicting that the world will get warmer, but exactly how much warmer or how quickly it will happen is still being debated (Box 3: Global warming and climate change).
A national and international issue
An increase in global temperature would bring changes to the entire planet, and therefore to every nation. This makes it an international issue which needs worldwide study and responses (Box 4: International deliberations). But individual countries are each responsible for their own greenhouse gas production. Australia produces about 1.5 per cent of the world's anthropogenic greenhouse gases. We have very high emissions of greenhouse gases relative to other developed countries, considering the size of our population and economy (Box 5: Australia's policy response). One of the reasons for this is that other nations have reduced their carbon dioxide emissions because they use more natural gas and nuclear power instead of oil and coal.
Australia and over 150 other countries signed the United Nations Framework Convention on Climate Change at the first Earth Summit held in Rio de Janeiro in 1992. This agreement set up a process which enabled governments to meet regularly to discuss action to avert extreme climate change. As a result of subsequent talks, all developed countries were asked to reduce their greenhouse gas emissions to 1990 levels. In December 1997, a conference of governments held in Japan attempted to reach legally binding agreements about what each country should do. The idea was for each country to reduce its greenhouse gas output by a similar percentage.
The Australian government argued that this was not fair on Australia because we have a different sort of economy from some other developed nations, and would suffer economic and social costs if we reduced our emissions by the same percentage as other countries. But if we used nuclear power or more natural gas or more renewable energy sources such as solar power then we wouldn't need to create so much carbon dioxide and other greenhouse gases.
There was also some dispute about the accuracy of the mathematical model used to calculate the effect of reducing our greenhouse gases. This is important because the government's argument was partly based on the predictions of this model.
Australian scientists are working on many aspects of the greenhouse effect. Some scientists try to determine climatic trends. Others model the effect of the enhanced greenhouse effect on Australia's climate and economy. Still others live and work on the Antarctic ice cap, to see what effect the enhanced greenhouse effect may be having there. All this is part of a worldwide attempt to better understand what may be causing global warming and to decide what can be done about it.
Related Academy Material
Geoengineering - can it help our planet keep its cool?
Acid test for the seas
Impact of global warming on biodiversity
Predicting natural events
Warmer and sicker? Global warming and human health
Getting into hot water global warming and rising sea levels
Coral bleaching will global warming kill the reefs?
Carbon currency the credits and debits of carbon emissions trading
The Southern Ocean and global climate
Interviews with Australian Scientists
Dr Garth Paltridge (Atmospheric science)
The Science of Climate change: Questions and Answers.
Page updatedFebruary 2012.