Under the Microscope: There is a general scientific consensus that the release of certain gases, principally carbon dioxide, into the atmosphere has significantly warmed the world. This is called the enhanced greenhouse effect, writes Prof William Reville.
There is also a consensus among earth system scientists that the surface of the earth, life on earth, and the atmosphere constitute one overall self-regulating system. This is close to accepting the well-known Gaia theory, which proposes that this system is regulated by living organisms so as to maintain the temperature of the earth at a comfortable level for life. Quantitatively, human life is but a minor component of the totality of life on earth, although with the capacity to influence Gaia out of all proportion to its own size.
James Lovelock, who proposed the Gaia hypothesis in 1972, warns us in his latest book, The Revenge of Gaia (Allen Lane, 2006), that we have so artificially altered the composition of the atmosphere that Gaia could now fail in its ability to maintain the earth's temperature at its present comfortable level for humanity. In that event, temperature regulation would switch over to a new equilibrium of sweltering heat with disastrous consequences for human civilisation. Lovelock proposes that our only hope of avoiding this awful scenario is to switch over right away to generating all our electricity from nuclear power which doesn't release any warming carbon dioxide gas.
The sun is the earth's only external source of energy. If the earth had no atmosphere, its surface temperature would resemble the moon ie soaring heat (107 degrees) during the day and deep freeze (-153 degrees) during the night. The earth has an atmosphere composed principally of nitrogen, oxygen and water vapour, plus trace amounts of carbon dioxide. Radiant energy from the sun passes freely through the atmosphere to heat the earth which re-radiates heat back into the atmosphere as longer wavelength infra-red radiation. Certain atmospheric gases, principally carbon dioxide and water vapour, absorb the radiation and trap much of the heat close to the earth, preventing it leaking out to space. This is the greenhouse effect.
Carbon dioxide levels in the air are controlled by living organisms who pump this gas out of the air through the process of photosynthesis by green plants and other organisms, and by non-living processes such as the oceans that dissolve carbon dioxide out of the air, and by the weathering of rocks. In the oceans organisms called algal plankton also release the gas dimethyl sulphide that is oxidised in air to form little particles that seed white clouds that act like white umbrellas to cool the earth during the day. Gaia theory proposes that this complex series of interactions, with the running made by living organisms, controls and maintains the temperature of the earth's surface to a level (average of 16 degrees) comfortable for life. Historical records going back 600,000 years show a close correlation between surface temperature of the earth and atmospheric carbon dioxide concentrations.
Life first appeared on earth almost four billion years ago. Since then the luminosity of our sun has increased by about 25 per cent, but in spite of this the surface temperature of the earth has remained temperate and hospitable for widespread life. The temperature on earth has been mainly maintained by regulating the concentration of carbon dioxide in the atmosphere through living organisms.
There is now no doubt that since the 19th century the concentration of carbon dioxide, and some other warming gases, eg methane, has risen dramatically due to society's emissions to the atmosphere. Measurement of air trapped in ice have shown that carbon dioxide concentrations in the atmosphere from 1,000AD to 1,800AD varied between 280 to 290 parts per million (ppm). Since the advent of the industrial revolution carbon dioxide concentrations have risen from 280 to 380ppm. The average temperature of the world has also risen, if rather erratically. It is now nearly one degree warmer on average than it was in 1850.
Human civilisation has drastically challenged Gaia by releasing massive amounts of greenhouse gases, by depleting the world's forests and vastly altering ecosystems in order to devote vast tracts of the earth to agriculture. Lovelock warns that we have infected Gaia with a fever which will soon progress to a coma when temperatures will rise by eight degrees in temperate regions and five degrees in the tropics. Most of the tropics will change into desert and there will be global flooding of coastal regions. Billions of people would perish in these conditions and the remainder would enjoy the comforts of the Middle Ages.
According to Lovelock, writing earlier this year in the London Independent, our only slim hope of avoiding this disastrous scenario is for everybody to immediately cut back on carbon dioxide emissions, but particularly the main emitters, the US, and the emerging economies of India and China. This is not likely to happen. An integral part of these changes would be an immediate switch over to generating electricity by nuclear power.
I am not sufficiently expert in meteorology, climatology, geology and Gaia theory to critically analyse Lovelock's predictions. He makes a powerful argument and the Gaia concept has proved itself to be a remarkably fruitful way to look at the whole earth system. I sincerely hope he has over-estimated the severity of the trends, but I fear it is unlikely he is seriously mistaken. If the clock is not about to chime midnight, it may well be at the 11th hour. We must end our profligate ways.
• William Reville is associate professor of biochemistry and public awareness of science officer at UCC - http://understandingscience.ucc.ie