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Science, People & Politics

Scince, Peple & Politics, issue 4, July - August 2008.

Disasters by Degrees

By Helen Gavaghan

Six Degrees, Our Future on a Hotter Planet
By Mark Lynas
Harper Perennial (2007)
346 pages, including index and notes
Paperback £8.99.

"These gases (greenhouse gases) cause a 'greenhouse effect' because they are opaque to long-wave infrared radiation: heat coming in from the Sun is short-wave, and so passes straight through, but when this heat is re-radiated by the Earth, its wavelength is longer, and some is trapped by the gases - just as glass in a greenhouse also traps heat."
pxix, Six Degrees: Our Future on a Hotter Planet, by Mark Lynas.

THE BOOK STARTS as well as does any mystery from a mistress such as P.D.James. "The knock on the door came at night. In the darkness I could see the yellow jackets over black uniforms - the police."

I was curious. How long could he sustain the pastiche and why was it needed? Perhaps because seamlessly he moved into science writing and I found myself immersed in the global warming debate, heading for the apocalypse of climate-change meltdown without realising I was being educated. I know the climate change debate is important but I have not always followed it as assiduously as I ought to, so I am pleased to write that this book fills in some important gaps for me. Its take home message is that we must confine man-made climate change to an increase of no more than one or two degrees. The alternate is a cascade of feedback mechanisms that sees the Earth change out of all current recognition (see commentary: Food and National Security.)

Between now and this disastrous future unknown emission scenarios are more significant than climate science uncertainties, an assertion which surprised me. Whatever we do, though, there is already 0.5 to 1° of heating in the pipeline, warns Lynas, and carbon dioxide stays in the atmosphere for about a century. Two pieces of informed speculation that are significant to the debate.

The structure of the book is to present a picture of how the world's environment, climate, ice cover, sea-levels and weather will look for each additional degree increase in the global average.

By six degrees, writes Lynas, there are few "clues" to what really lies in store. Still he has a go. Looking to extreme Greenhouse episodes in the Earth's distant past we learn that between 144 and 65 million years ago, when ferns and conifers dominated the land, rocks containing fossilised trees suggest temperatures some 10 to 15 degrees higher as a global average then than now. Informed analysis based on fossil records and on models suggests carbon dioxide levels were three to six times today's levels, mainly because of volcanic activity as the giant continent Pangaea split. The Earth then was a very different place, with only 80% of its current land mass in existence. Ocean currents would have been unrecognisable because land forms no longer in existence generated them and fewer mountains guided winds. To all intents and purposes the Earth during the cretaceous was a different planet. So when Lynas writes that frosts were either rare or unknown on the edge of the Arctic ocean there really is very little in terms of obvious relevant lessons and warnings should today's Earth end up six degrees warmer on average than it is now. Today volcanic activity accounts for only two per cent of atmospheric carbon dioxide and human beings are responsible for carbon dioxide being released at a rate of about a million times that of its sequestration by geological structures and processes during the cretaceous. By contrast also with the lushness of the cretaceous Lynas writes that with equivalent warming globally of six degrees today's Earth is set for mass extinction.

Earlier chapters take the reader step by step through global average temperature increases from 2 to 5 degrees. Processes hypothesized for each step are what tip Earth into climate change disaster. One scarcely needs such awful warnings of worst case scenarios because conditions at only one degree to two degrees above those of now are bad enough news. Take a study of the Hadley Centre at the British Meteorological Office. This suggest that the incidence of moderate drought would double by 2100 in the one degree world, and that extreme drought would cover 30% of the Earth's surface compared with 3% today. "In essence a third of the land surface of the globe would be largely devoid of fresh water and no longer habitable to humans," he writes.

Patterns of inhabitability are not always bad news when they change. A wobble in the Earth's orbit around the Sun some 9000 to 6000 years ago heated the northern hemisphere slightly more than the southern, bringing monsoons to water harvests in northern Africa. What is now the uninhabitable Sahara, where scorching temperatures of 58°C have been recorded, then hosted buffalo and gazelles. Perhaps the Sahara, large enough to engulf the contiguous US can again become a habitable zone.

Saharan climate and habitation history illustrates a dilemma for scientists. The debate is about global warming, but which climate data is regional, and, given the complexity and sensitivities of the interconnected Earth system and its responsiveness to solar activity and position, the past is only a moderately good guide to the future. This is not to deny the reality of the man-made global warming, but to say plate tectonics, shifting continents and orbital mechanics do have a non man-made contribution to make. The Sun itself is getting hotter, increasing solar radiation just as Human activity is trapping more radiation.

In a two-degree world oceans hover on the brink of being mildly acidic so molluscs may loose their favourable watery niche and shell making environment. Adaptation may not enable species to cope, and the timescales of climate change are too short for evolution. Phytoplankton, for example, loose the upwelling nutrients that nourish them. Lynas quotes biological oceanographere, Katherine Richardson from Aarhus University in Denmark, as saying, "we are altering the entire chemistry of the oceans without any idea of the consequences."

The whole of this book is filled rightly with such cheerless prognostications. But he does not ask his readers to abandon hope. Lynas recognises and says if we act now we can avoid disaster.