The European Commission is about to launch a new awareness campaign on climate change. The body of scientific evidence showing that the phenomenon of ‘global warming’ is causing real harm to our planet is incontrovertible. In this feature we examine ‘The Enhanced Greenhouse Effect’
The Greenhouse Effect
Energy from the sun warms the Earth’s surface and, as the temperature increases, heat is radiated back into the atmosphere as infra-red energy. Some of the energy is absorbed within the atmosphere by “greenhouse gases”. The atmosphere thus acts in a similar way to the walls of a greenhouse, letting in the visible light and absorbing the outgoing infra-red energy, thus keeping it warm inside.
Most of the greenhouse gases occur naturally. Water vapour and carbon dioxide are by far the most important natural greenhouse gases and have been the Earth’s mechanism for maintaining a liveable temperature. However, since the industrial revolution, human society too has been producing greenhouse gases, particularly carbon dioxide, methane and nitrous oxide. As a result, their concentrations in the atmosphere are now higher than at any time in the past 420,000 years. This means rising temperatures on Earth. This man-made extra warming is called the “enhanced” greenhouse effect.
Carbon dioxide: The main contributor to the enhanced greenhouse effect is carbon dioxide (CO2). Globally, it accounts for over 60 per cent of the enhanced greenhouse gas effect. In industrialised countries, CO2 makes up more than 80 per cent of greenhouse gas emissions.
Many billions of tonnes of carbon are exchanged naturally each year between the atmosphere, the oceans and land vegetation. Carbon dioxide levels in the atmosphere appear to have varied less than 10 per cent during the 10,000 years before the Industrial Revolution. Since 1800, however, concentrations have risen by about 30 per cent as massive amounts of fossil fuels are burned to produce energy. Currently we are emitting more than 25 billion tonnes of CO2 into the atmosphere each year.
Methane: The second-most important greenhouse gas for the enhanced greenhouse effect is methane (CH4). Since the beginning of the Industrial Revolution, atmospheric methane concentrations have doubled and contributed some 20 per cent to the enhancement of the greenhouse gas effect. In industrialised countries, methane accounts typically for 15 per cent of greenhouse gas emissions.
Methane is created predominantly by bacteria that feed on organic material where there is a lack of oxygen. It is therefore emitted from a variety of natural and human-influenced sources, with manmade emissions accounting for the majority. Natural sources include wetlands, termites, and oceans. Human-influenced sources include the mining and burning of fossil fuels, livestock husbandry, rice cultivation and landfills.
In the atmosphere, methane traps heat and is 23 times more effective at that than CO2. Its lifetime is however shorter, between 10 and 15 years.
Nitrous oxide: Nitrous oxide (N2O) is released naturally from oceans and rainforests and by bacteria in soils. Human-influenced sources include nitrogen-based fertilisers, fossil fuel combustion and industrial chemical production using nitrogen, such as sewage treatment. In industrialised countries, N2O accounts for around six per cent of greenhouse gas emissions. Like CO2 and methane, nitrous oxide is a greenhouse gas whose molecules absorb heat trying to escape to space. N2O is 310 times more effective than CO2 absorbing heat. Since the beginning of the Industrial Revolution, nitrous oxide concentrations in the atmosphere have increased by about 16 per cent and contributed 4 to 6 per cent to the enhancement of the greenhouse effect.
Fluorinated greenhouse gases: These are the only greenhouse gases that do not occur naturally, but have been developed by man for industrial purposes. Their share of greenhouse gas emissions from industrialised countries is around 1.5 per cent. But they are extremely powerful – they can trap heat up to 22,000 times more effectively than CO2 – and they can stay in the atmosphere for thousands of years.
Fluorinated greenhouse gases include hydrofluorocarbons (HFCs) which are used in cooling and refrigeration, including air conditioning; sulphur hexafluoride (SF6), which is used, for example, in the electronics industry; and perfluorocarbons (PFCs), which are emitted during the manufacture of aluminium and also used in the electronics industry. Arguably the best known of these gases are chlorofluorocarbons (CFCs), which are not only fluorinated greenhouse gases, but also deplete the ozone layer. They are being phased out under the 1987 Montreal Protocol on Ozone-Depleting Substances.
Conclusion
Since the industrial revolution, the concentration of greenhouse gases in the atmosphere has risen by more than 50 per cent. Over the last century, the average global temperature has increased by 0.6°C, while the average temperature in Europe has increased by almost 1°C. Globally, the five hottest years ‘on record’ have been, in this order: 1998, 2002, 2003, 2004, and 2001.Climate experts project that this trend will accelerate, with the average global temperature increasing by between 1.4° and 5.8°C by 2100.
The result of this process is that polar ice caps are melting and glaciers are retreating. Consequently, Sea levels are rising, biodiversity is being lost, food production is threatened and the scarcity of clean drinking water is spreading. The weather is becoming more extreme, with storms, floods, droughts and heat waves occurring more frequently and negatively affecting the economy. There is an increase risk of disease spreading and of societies being forced to tackle water and food shortages, possibly conflicts and migration. Finally, catastrophic disruptions might occur through worst-case scenarios, such as a sea-level rise of seven metres due to the melting of the Greenland ice sheet.
Barbara Helfferich is spokesperson for Environment for the European Commission, Commissioner S. Dimas.