The Emerald Planet by David Beerling

Author:David Beerling
Language: eng
Format: epub
ISBN: 9780192529787
Publisher: OUP Oxford
Published: 2016-12-29T16:00:00+00:00

In his research on gases, Tyndall convincingly demonstrated that ‘perfectly colourless and invisible gases’ differed enormously in their abilities to absorb radiant heat. He correctly identified carbon dioxide, methane, nitrous oxide, and ozone as effective greenhouse gases and noted that neither oxygen, nitrogen, nor hydrogen had any significant greenhouse properties.30 The energy in infrared radiation (Tyndall’s radiant heat) was insufficient to break the chemical bonds within the molecules of the gases and split them apart into their constituent atoms. Consequently, it excited the molecules in those gases with an asymmetrical arrangement of three atoms (carbon dioxide, nitrous oxide, and ozone), increasing molecular vibrations that transfer heat to the air when the molecules collide. Methane, nitrous oxide, and ozone, are all potent greenhouse gases despite being present in the atmosphere at relatively low concentrations because, molecule for molecule, they are more effective ‘heat trappers’ by operating in an uncluttered part of the electromagnetic spectrum. In fact, methane, nitrous oxide, and ozone are, in that order, about 25, 200, and 2000 times more effective at causing planetary warming than carbon dioxide.31

All this must have been exciting enough, but Tyndall’s most startling discovery was that of the important greenhouse gas water vapour. He was stunned to find it absorbs 80 times more heat (infrared radiation) than pure air and was quick to realize its importance for climate. ‘Water vapour’, he said, ‘acts more energetically upon the terrestrial rays than the solar rays; hence, its tendency is to preserve to the earth a portion of heat that would otherwise be radiated into space’.32 Alert to its profound climatic significance, he commented,

this aqueous vapour is a blanket more necessary to the vegetable life of England than clothing is to man. Remove for a single summer‐night the aqueous vapour from the air which overspreads this country, and you would assuredly destroy every plant capable of being destroyed by a freezing temperature. The warmth of our fields and gardens would pour itself unrequited into space, and the sun would rise upon an island held fast in the iron grip of frost.33

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