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ISIS Special Miniseries - Back to the Future for Gaia

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The Institute of Science in Society

Science Society Sustainability

http://www.i-sis.org.uk

 

General Enquiries sam

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ISIS Director m.w.ho

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ISIS Special Miniseries

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Back to the Future for Gaia

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The projected increase in carbon dioxide level in the atmosphere is without

precedent over the past 12 million years or more. Peter Bunyard reports.

 

Diagrams and sources for this article are posted on ISIS Members’ website.

www.i-sis.org.uk\Membership

 

One way to see the future is to look at the distant past, even 100 million years

ago. For if we continue to burn fossil fuels and deforest at the current rate,

then within a century we might find ourselves with greenhouse gas concentrations

in the atmosphere and surface temperatures similar to those of that ancient

past.

 

 

Fifty million years ago, the planet had little ice, yet global temperatures were

on average no more than 5 C warmer than today. Equally relevant, CO2 levels in

the atmosphere were probably no higher then than has been projected for the more

extreme scenarios projected by the IPCC (see box)

 

IPCC

The Intergovernmental Panel on Climate Change has been established by United

Nations agencies, World Meteorological Organization and the United Nations

Environment Program to assess the risks of global warming from scientific,

technical and socio-economic information, and to consider the options for

adaptation and mitigation. The IPCC consists of more than 300 leading

international scientists.

 

 

Before we blithely brush off concerns about a warmer planet, it is worth noting

that 50 million years ago, sea levels were several hundred feet higher than they

are today. Most of that water is now locked away in Antarctica and Greenland. If

these ice sheets were to melt, Denmark and large parts of eastern Britain and

Holland would vanish in their entirety, as would many other places. We would

have considerable difficulty surviving, not least because of extreme weather

conditions, and the loss of vast areas of cropland to produce food.

 

 

Given that we have records of surface temperatures and precipitation patterns

going back a few centuries at best, how can we possibly lay claim to knowing

what the earth’s climate was like, hundreds of thousands if not millions of

years ago?

 

 

That is where the Antarctic comes in, not only because of its 2,400 metre thick

cap of ice, which covers 14 million square kilometres, but also because of

sediments off the land mass at Cape Roberts in the Ross Sea. The ice, like that

drilled at the Russian Base, Vostok, yields information going back 400,000 years

on temperature, CO2 content, sea-level. The sediments, overlying Beacon

sandstone of the Devonian, are 1500 metres thick, dating from 34 to 17 million

years ago until the present. Meanwhile, drilling 100 metres into the underlying

sandstone takes one back still further, even beyond 100 million years ago.

 

 

Peter Barrett, from New Zealand’s Antarctic Research Centre at Victoria

University, has been member of a team of some 55 scientists from Australia,

Britain, Germany, Italy, Netherlands, New Zealand and the USA, who investigated

the sediments. He points out that “Global climate, even in 50 years’ time, may

be warmer than the earth has experienced in the past 12 million years.”

 

 

From tree stumps, fossils, leaves and coal seams, we know that 200 million years

ago Antarctica was covered in forests and swamps. Antarctic temperatures then

were at least 15 C warmer than today and, consistent with that, global

temperatures some 7 or 8 C warmer than now.

 

 

Two distinct factors may have been responsible then for a warmer,

vegetation-covered Antarctica. During the Cretaceous and Early Cenozoic, between

136 and 54 million years ago, we know that atmospheric CO2 was high and

certainly responsible for part of the warming. The other factor relates to

Antarctica still being part of Gondwanaland, a gigantic joined up

super-continent landmass that included Australasia and the Indian Sub-continent.

Once that super-continent began to break up, Antarctica became increasingly

cut-off by a strong polar air circulation system and consequently a cold

circum-polar ocean current.

 

 

Whichever was more decisive - a falling concentration of greenhouse gases or the

increased isolation in the polar extremity - the first ice-sheets formed over

Antarctica 34 million years ago. And then, as the earth cooled still more some

2.5 million years ago, the ice-sheet formed for the first time over Greenland in

the Northern Hemisphere. From then on, we have had ice ages affecting both

poles.

In all probability, the cold circum-polar current contributed most to the

chilling of Antarctica, in which case it might take more than elevated CO2

levels to bring about a complete melting of the ice-sheet.

 

 

Yet, as the ice-core data shows, the expansion and retreat of the ice-sheet

during the glacial and inter-glacial periods have always been associated with

swings in temperature that themselves correlate closely with levels of CO2 in

the atmosphere. Some 18,000 years ago, when the last ice age was at its most

intense, CO2 levels were 30 per cent below 1900 levels and sea-level was 120

metres below present sea-level.

 

 

That should warn us that whatever regulates greenhouse gas concentrations in the

atmosphere could have profound effects on climate. In fact, we do not know which

triggers which: whether CO2 concentrations in the atmosphere trigger climate

change or whether climate change triggers CO2 concentrations. In all likelihood

one affects the other, which then feeds back in a mutual dynamic process.

 

 

Until 800,000 years ago, the glacial cycle lasted some 40,000 years, but then

lengthened into the current 100,000 cycle. The two periodicities, 40,000 years

and then 100,000 years happen to conform respectively to the changing obliquity

and eccentricity of the earth’s orbit, both of which determine changes in the

pattern of solar energy reaching the earth.

 

 

The orbital changes, including the swinging of the earth from side to side in

its axial precession, comprise what has been called the Malenkovitch Wobble. Few

scientists question that it influences the seasons and global climate. Moreover,

the Antarctica data are the best record we have showing correspondence between

the retreat and then re-establishment of the ice sheet with where the earth is

at regarding its orbit around the sun.

 

 

But one factor has been largely overlooked: the role of the biosphere in

modulating climate through its impact on the atmosphere and the concentration of

the prime greenhouse gases such as carbon dioxide, methane and even water

vapour. And when life is doing well, as James Lovelock realized in formulating

his Gaia hypothesis, then CO2 levels tend to be low, thereby reflecting a

greater intensity of primary photosynthetic productivity by green plants. Hence

his famous remark: “life prefers it cold.”

 

 

Lovelock was referring in particular to the cloud-forming characteristics of

certain algae - namely the coccolithophores - which contribute significantly to

the cooling of the earth’s surface, especially over the oceans. Simultaneously,

they are responsible for drawing down CO2 in photosynthesis and depositing it as

calcium carbonate on the ocean floor. The White Cliffs of Dover are none other

than CO2 made solid, mostly by life and hence taken out of the atmosphere for

geological periods of time. This is a very important carbon sink.

 

 

Plankton activity of the past leaves its mark in the ice-core record. When

plankton are thriving, the concentrations of CO2 in the atmosphere, as found in

bubbles of air entrapped in the ice, go down; on the other hand, when

phytoplankton activity is depressed, which appears to be correlated with

inter-glacial periods, then CO2 levels rise (Fig. 1 & Fig. 2). If it were not

for phytoplankton activity, then atmospheric levels of CO2 in the pre-industrial

era would likely have been 450 parts per million rather than the actual level of

280 ppm.

 

In a theory of climate that embraces the role of life, could it be pure

coincidence that ice-ages show plankton activity at a peak and that northern

peat bogs show peak storages of carbon when the climate is colder? Could it be

that as the earth wobbles, drifts and swings its way around the sun, life takes

advantage of the changing conditions, either embarking on a spate of

photosynthetic activity, which deposits organic carbon or, on the contrary,

suddenly embarking on a feverish burning up of the surplus store of carbon? Both

activities, photosynthesis and respiration, would take off as conditions suited

them, until running out of ‘steam’, when orbital changes would initiate a new

cycle of change. Could it be that the change 800,000 years ago from a 40,000

glacial cycle to one of 100,000 years came about because life extended the time

during which greenhouse gases were kept down in the atmosphere?

 

 

The evidence from polar ice is of sudden spurts in the emissions of greenhouse

gases from purely natural sources, with temperature increasing in tandem.

Positive feedback mechanisms are clearly at work yet, because of our ignorance,

they are nowhere to be seen in the current general climate models that the IPCC

uses to predict future climate change. If we are to learn anything from the

distant past it is that we should take all precautions not to perturb a system,

which at some unknown critical point, jumps violently into a very different

state. That vast polar continent, sheared off from the rest of the living world,

has issued its warning.

 

 

 

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General Enquiries sam

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ISIS Director m.w.ho

 

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