This month, the earth passed a worrying milestone. The amount of carbon dioxide in our atmosphere exceeded a concentration of 400 parts per million (ppm) by volume for the first time in many millions of years. This concentration represents an increase of 40 per cent above that of pre-industrial times, a matter of serious concern. The last time the earth had this amount of carbon dioxide in its atmosphere, the poles were ice-free and sea levels were 40metres higher.
Greenhouse effect
Scientists have long been aware that the earth's climate is very sensitive to certain gases in the atmosphere such as carbon dioxide (CO2). These "greenhouse gases" trap some of the heat radiated from the earth's surface, keeping the globe at a warm temperature. So far so natural, but it is now established beyond doubt that emissions from the burning of fossil fuels have increased the concentration of atmospheric greenhouse gases far beyond natural levels. It's hard to see how such a change would not affect global climate and sure enough, the increase in CO2 has been found to correlate tightly with the phenomenon of global warming. Climate scientists have warned of this problem for many years but greenhouse gas emissions have actually accelerated, from an increase of 0.7 ppm per year in the 1960s to 2.1 ppm per year today.
Physicists predict that the increase in atmospheric CO2 will result in a rise in average global temperature of least 2 degrees. This may not sound like much, but such a rise in average temperature corresponds to large changes such as increasing desertification in some parts of the world, permanent flooding in others and erratic weather patterns worldwide. As temperatures rise, many millions of people will be forced to leave their homelands, causing untold hardship and regional conflicts around the globe.
Is there any letup?
As pointed out in a recent article in the Economist, global surface temperatures have not risen appreciably in the last 10 years. This leads the Economist to question our understanding of the response of the earth to a rise in greenhouse gases. Perhaps our climate is not as sensitive to them as we thought and perhaps we need not worry so much about emissions?
This attractive idea has been widely cited, but the Economist is not a scientific authority and it is probably a false hope. In the first instance, a decade is a very short time in climate science. Second, it is only surface temperatures that have stabilised somewhat in recent years. This does not include the absorption of heat by the oceans, thought to comprise about 90 per cent of global warming. Most of our planet lies under water and the warming of the deep oceans will have serious consequences for marine life and for sea levels (water expands when heated).
Third, temperature is not always a good measure of heat. There can be a significant time lag between heat absorption and temperature rise (particularly in the case of water because it has a high specific heat capacity). Another effect is where heat absorption occurs without a change in temperature, as happens when ice melts. Just such a process is already under way on a massive scale in the Arctic and the Antarctic. The ongoing loss of land ice at the poles is a matter of great concern as it is expected to raise sea levels further and to reduce the ability of the planet to reflect heat, resulting in yet more warming.
A tough solution
It seems there is no alternative but to wean ourselves off fossil fuels. This will not be easy as the world's population continues to grow and developing countries continue to industrialise. Another problem is a widespread public scepticism concerning the reality of human-induced climate change, fanned by fossil fuel lobbyists and right-wing political interests opposed to government regulation. It is a matter of great concern that, heedless of the findings of science, many conservative politicians in the US, Canada, Australia and the UK oppose action on climate change just as they did 30 years ago.
Ironically, great progress has been made in the efficiency of low-carbon technologies such as wind, solar and wave energy in recent years. Whether realpolitik will allow governments to prioritise investment in the low-carbon industry in time to avoid the worst effects of irreversible climate change remains an open question.
Dr Cormac O'Raifeartaigh lectures in physics at Waterford Institute of Technology and writes science blog Antimatter