Courtesy of Environmental Defence
The greenhouse effect
The atmosphere has a natural supply of greenhouse gases. They capture heat and keep the surface of the Earth warm enough for us to live on. Without the greenhouse effect, the planet would be an uninhabitable, frozen wasteland.
Before the Industrial Revolution, the amount of carbon dioxide (CO2) and other greenhouse gases released into the atmosphere was in a rough balance with what could be stored on Earth. Natural emissions of heat-trapping gases matched what could be absorbed in natural sinks. For example, plants take in CO2 when they grow in spring and summer and release it back to the atmosphere when they decay and die in autumn and winter.
Turning up the heat
Industry took off in the mid-1700s and industrialised countries started emitting large amounts of greenhouse gases. Fossil fuels were burned more and more to run cars, trucks, factories, planes and power plants, adding to the natural supply of greenhouse gases. The gases — which can stay in the atmosphere for at least 50 years and up to several centuries — are building up beyond the Earth's capacity to remove them and in effect, creating an extra-thick heat blanket around the Earth.
The result is the globe has heated up by more than half a degree centigrade over the past century — and it has heated up more intensely over the past two decades. If half a degree doesn't sound much, consider this: the difference in global average temperatures between modern times and the last ice age was only around five degrees centigrade. So in fact 0.5 degrees is very significant, especially since the unnatural warming will continue as long as we keep putting extra greenhouse gases into the atmosphere.
How much is too much?
Already, human beings have increased the amount of CO2 — the chief global warming pollutant — in the atmosphere to 31 percent above pre-industrial levels. There is more CO2 in the atmosphere now than at any time in the last 650,000 years. Studies of the Earth's climate history show that even small changes in CO2 levels generally trigger significant shifts in the global average temperature.
Scientists expect that, in the absence of effective policies to reduce greenhouse gas pollution, the global average temperature will increase at least another one degree centigrade by 2100.
Even if the temperature change is at the small end of predictions, the alterations to the climate are expected to be serious: more intense storms, more pronounced droughts, coastal areas more severely eroded by rising seas. At the high end of the predictions, the world could face abrupt, catastrophic and irreversible consequences.
The science is clear
Scientists are no longer debating the basic facts of climate change. In February 2007, thousands of scientific experts collectively known as the Intergovernmental Panel on Climate Change (IPCC) concluded it is more than 90 percent likely that global warming is caused by humans. (IPCC, 2007)
The IPCC's latest findings amplify what other highly respected science organisations say. In a joint statement with 10 other National Academies of Science, the US National Academy of Sciences said:
"The scientific understanding of climate change is now sufficiently clear to justify nations taking prompt action. It is vital that all nations identify cost-effective steps that they can take now, to contribute to substantial and long-term reduction in net global greenhouse gas emissions." Joint Statement of Science Academies: Global Response to Climate Change, 2005
The American Geophysical Union, a respected organisation comprising over 41,000 Earth and space scientists, wrote in its position on climate change that "natural influences cannot explain the rapid increase in global near-surface temperatures observed during the second half of the 20th century."
(c)Environmental Defense; reprinted by permission. For information, write Environmental Defense, 257 Park Avenue South, New York, NY 10010; or e-mail members@environmentaldefense.org, or visit our English-language web site at www.environmentaldefense.org
