The Greenhouse Effect and Global Warming

It has become clear to the overwhelming majority of scientists from many different fields that the key factor in the greenhouse effect and global warming is the noticeably increased amount of carbon dioxide - CO2 - in the atmosphere. Although to us it seems huge, our atmosphere is in fact incredibly thin - as Robert Henson (2006, p.7) explains "if you picture Earth as a soccer ball, the bulk of the atmosphere would be no thicker than a sheet of paper wrapped around that ball." We have for a number of years been aware that human emissions can cause damage to our atmosphere, most notably emissions of CFCs (chlorofluorocarbons) creating the hole in the ozone layer. The greenhouse effect is, however, entirely different from this, although it is similar in the sense that it has been caused by our emissions.

Radiation comes to Earth from the Sun, and without it there would be no life on Earth. Almost 50% of the sunlight gets absorbed by the Earth's surface, while about 30% of it gets reflected back into space. The Greenhouse Effect occurs when some of that radiation is trapped from escaping, and is instead radiated back towards the Earth. We now know that certain greenhouse gases cause this effect - carbon dioxide, methane, nitrous oxide, water vapour and others. The higher the presence of these gases in our atmosphere, the greater the Greenhouse Effect, and thus the higher the Earth's average temperature becomes.1

Some gases are more powerful greenhouse gases than others - methane and nitrous oxide are more powerful,2 but are present in much smaller quantities in the atmosphere and in our emissions. It is the sheer amount of carbon dioxide pouring into the atmosphere that has caused an increased Greenhouse Effect, amongst other matters of concern which we shall look at shortly. Before the Industrial Revolution there were around 270-280ppm (parts per million) of CO2 in the atmosphere. This amount has varied, and from ice core samples from the Antarctic, we know that increased carbon dioxide is always in tandem with increased temperatures on Earth. Fifty years ago, the amount of carbon dioxide in our atmosphere increased at around 1ppm per year, whereas now the rate is around 3ppm. The IPCC (Intergovernmental Panel on Climate Change) predicts by 2100 that there could be as many as 970ppm if we continue to emit CO2 at predicted trends.

Much of the increase in CO2 levels has arisen due to the burning of fossil fuels, although interestingly this has also alleviated some of the problem by a phenomenon known as Global Dimming. The particles that pour from coal-fired power plants, cars, planes and factories block some of the sunlight from entering the atmosphere in the first place, and thereby lead to slightly cooler temperatures.3 However, this effect is much smaller than the Greenhouse Effect, and cannot be relied upon to bring balance to the heating that is increasing.

1. For a more in depth explanation of the greenhouse effect look at Henson (2006), p. 20f., Dow and Downing (2007), p. 30, Flannery (2005), p. 20f.
2. Methane is twenty times more powerful than carbon dioxide, nitrous oxide is three hundred times more powerful (Dow and Downing (2007), p. 44)
3. Flannery (2005), p.126