Earth's atmosphere comprises many gases: oxygen, nitrogen, carbon dioxide (hereafter abbreviated to CO2) and water vapour, to name a few. These gases are collectively called greenhouse gases and they keep the Earth's temperature at a comfortable 15°C. Without them Earth would be a chilly -18°C.

Since pre-industrial times, usually taken to be before 1750, we know from ice-core records that CO2 levels were about 280 ppm,that's 280 parts of CO2 per million parts of air. As industrialisation got underway humankind started to farm the land more intensely than ever before, which included deforestation for agriculture and settlements. Later - since about 1850 or so - the burning of fossil fuels for energy and transport has added considerably to greenhouse gas levels, particularly CO2.

This has resulted in CO2 levels increasing to about 385 ppm, a rise of about thirty-seven per cent from pre-industrial levels - mainly as a result of burning fossil fuels.

How do we know this?

Well, data from ice-core records that go back at least 650,000 years now show us that CO2 levels have fluctuated naturally during this time between 280 and 300 ppm. CO2 levels have also been measured accurately from the top of Mauna Loa Volcano in Hawaii since 1958, and results show an increase in CO2 levels from 315 ppm to 385 ppm since that time.

Therefore CO2 is now at eighty ppm more than it has been for at least 650,000 years of Earth's history. It is a known scientific fact that higher levels of greenhouse gases will lead to higher temperatures, which appears to be happening now. The world has warmed by an average of 0.74 degrees during the last 100 years or so. As a result of this warming, polar ice has started to decrease and melt, and so have Earth's land-based glaciers. This in turn is causing sea levels to rise, which is putting low-lying islands at risk of flooding or total submersion, and will eventually threaten more and more of the world's coastal cities and regions.

Things may get worse, however, because once Earth's atmosphere starts to warm, the warming itself may cause further positive feedback mechanisms to kick in. A warmer atmosphere holds more water vapour, which is itself a powerful greenhouse gas. This will in turn cause further warming, and so on.

Melting ice results in more sunlight being absorbed by the surrounding 'darker' water and land, and that results in further warming, and more melting ice. Methane deposits currently held in a frozen but stable state under the sea and under the permafrost may be released as the oceans warm and permafrost melts, which will cause further warming. This is very worrying as methane is a potent greenhouse gas and around twenty times more powerful than CO2 when talking about it's ability to warm the Earth's atmosphere.

This is global warming in a nut shell, however there are of course far more complex issues involved as global warming will not affect the whole planet in the same way at the same time. Some parts will experience more drought, some parts more rainfall, and some parts more extreme weather such as floods and heatwaves.

One thing is for sure,as the world warms, we will all know about it...

Copyright (c) 2008 Simon Rosser