What a Wonderful World by Marcus Chown

Author:Marcus Chown [Marcus Chown]
Language: eng
Format: epub
ISBN: 9780571278428
Publisher: Faber & Faber
Published: 2013-03-25T16:00:00+00:00

Greenhouse warming

Carbon dioxide is of course the gas that is produced by the burning of fossil fuels such as oil and coal and whose concentration in the atmosphere has been increasing since the beginning of the industrial age. Over precisely the same period the global temperature has been steadily rising – exactly what would be expected since carbon dioxide is known to trap heat in the atmosphere.

It works this way. Carbon dioxide – and the rest of the gases that compose the atmosphere – are transparent to visible light from the Sun (if they were not, we would not be able to see the Sun). Sunlight therefore passes through the air unhindered and heats the ground. The ground, in turn, heats the air, which is why the temperature is highest near the ground and steadily decreases with altitude all the way to the top of the troposphere, the domain of weather.

To be precise, the ground glows with heat radiation typical of a body at about 20 °C. Crucially, such far infrared is absorbed by carbon dioxide in the atmosphere. In other words, the Earth’s heat is prevented from escaping into space and is instead trapped in the atmosphere. This is not quite what happens in a greenhouse, where glass is transparent to sunlight but provides a physical barrier to the escape of rising, or convecting, warm air. Despite this, however, carbon dioxide is widely known as a greenhouse gas.

Actually, by far the most important greenhouse gas in the atmosphere is water vapour. This is responsible for about 75 per cent of the warming effect of the atmosphere compared with only 20 per cent for carbon dioxide. We should on the whole be grateful for greenhouses gases since, without them, the average temperature of the Earth would be a super-chilly -18 °C.

However, if humans continue adding more and more carbon dioxide to the atmosphere, the global temperature will continue to rise. ‘Geological change usually takes thousands of years to happen but we are seeing the climate changing not just in our lifetimes but also year by year,’ warned the English chemist James Lovelock.

The Greenland ice sheet and Antarctic ice sheet are already melting. But the melting will accelerate, significantly raising the sea level globally and inundating low-lying coastal areas. The circulation of the ocean and atmosphere will change unpredictably, with worrying implications for the Earth’s 7 billion people. Nobody knows where it will all end. However, nature has conveniently shown us one possibility: Venus.

Being about two-thirds of the Earth’s distance from the Sun, Venus lost its water early on in its history. Basically, the extra heat from the Sun caused its primordial oceans to begin evaporating away. Water vapour, being a potent greenhouse gas, warmed the planet more, which evaporated more of the oceans, which warmed it even more, and so on. This runaway greenhouse effect, first proposed by Carl Sagan and William Kellogg in 1961, eventually boiled away Venus’s oceans entirely. We see no sign of them today because, at

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