The movement of the Earth’s tectonic plates has a profound influence on the climate. It is believed that when the Earth was formed most of the Planet was covered by water and that land masses began to form only slowly during Earth’s history. It is not known where the continents first began to form, “It is not yet possible to draw map of the continents prior to about 350 million years ago because the distance between the fragments that collided to form Pangaea prior to their collision cannot be estimated.” (The Times Concise Atlas of the World p.9).

The first known location of the Earth’s continents indicate that they were far away from those they have today, “A bit less than 500 million years ago glaciers were active in what is now the Sahara Desert, while it lay at the South Pole. Africa and North America were then about 10,000 kilometres apart.” (Preston Cloud ‘Cosmos, Earth and Man. A Short History of the Universe’ Yale University Press New Haven 1978 p.107).

About 300 million years ago there were only two continents: laurasia which consisted of eurasia, greenland and north america, and gondwanaland which consisted of all other continents. These two giant continents sidled towards each other to create a gigantic supercontinent called pangaea surrounded by one super ocean panthalassa, “Pangaea was itself formed some 250-300 million years ago by a collision of Gondwanaland with Laurasia west of the Urals and of Asia east of the Urals.” (The Times Concise Atlas of the World p.9). Quite why the two large continents merged together and how long the process went on for is not known. Similarly it is not known why pangaea began to break up. Laurasia still existed even a mere 80 million years ago. Eventually laurasia began to disintegrate and the continents drifted towards their current locations. Some of these continents drifted thousands of mile apart whilst others collided with each other producing some fantastic results, “Of all the dramatic motions (of plate tectonic) .. the most remarkable is that of India. Wedged free from its position between southeastern Africa and northern Antarctica about 150 million years ago, it has since then travelled some 8,000 kilometres northward to collide with southern Asia and elevate the world’s highest mountains.” (Preston Cloud ‘Cosmos, Earth and Man. A Short History of the Universe’ Yale University Press New Haven 1978 p.108).

The changing position of the continents around the Earth not only had a considerable impact on the continents’ climates but on that of the Earth as well, “The positioning of continents helped determine climatic conditions.” (Jon Erickson ‘Greenhouse earth. Tomorrow’s Disaster Today’ Tab Books, Blue Ridge Summit PA 1990 p.17); “The movement of continents itself affects the global climate because of the change in the distribution of the Earth’s albedo and because of the difference in the way land and sea warm and cool.” (Michael Allaby ‘Living in the Greenhouse’ Thorsons Publishing Group 1990 p.72).

Although the sun bathes the Earth in heat it is global warming which keeps the Earth warm not direct sunlight. Global warming retains some of the sun’s heat preventing it from making an immediate escape back into space. Global warming[1] is composed of three different factors.

Over the last decade or so a number of scientists have attempted to discover how the amount of the greenhouse gas CO2 has varied over time. The evidence derived from ice core samples in the Antarctic seems to suggest that variations in the level of atmospheric Carbon roughly match the variations in global temperature. Although the greenhouse effect is composed of a number of different greenhouse gases, many scientists seem to have focussed upon CO2 as the key gas which acts almost like the Earth’s thermostatic device - a rise in atmospheric CO2 boosts global temperatures whilst a decline causes a reduction in global temperatures .. “carbon dioxide in the atmosphere functions as a sort of thermostat for the Earth.” (Jon Erickson ‘Greenhouse Earth. Tomorrow’s Disaster Today’ Tab Books, Blue Ridge Summit PA 1990 p.16).

The Antarctic findings have been criticised, however, by scientists who argue the match is not always good and that in some cases the fall in Carbon happened after the fall in temperatures, “The fall in carbon dioxide did not occur until about 10,000 years after the temperatures began to plummet, at the start of the last ice age, so it was following rather than leading the trend.” (Nigel Calder ‘Spaceship Earth’ Viking, London 1991 p.192).

There is no conclusive evidence as yet about the link between the level of atmospheric CO2 and global temperatures. If an increase in atmospheric Carbon tends towards a rise in global temperatures but other, more powerful factors, cause an actual decrease in global temperatures then the greenhouse effect is still valid but clearly it is not powerful enough to warrant being called the Earth’s thermostat. It may be that the greenhouse effect produces a rise in temperature which causes an ice age.[2] If, however, an increase in atmospheric Carbon is not a cause of, but the effect of, a rise in global temperatures then this would undermine the greenhouse theory. The concentration of atmospheric CO2 might still play a role in influencing global temperatures (for example by helping to maintain the rise in temperature), but the theory of the greenhouse effect would be wrong because CO2 would no longer be a cause of temperature change. Proving whether a change in the concentration of atmospheric Carbon is a cause or an effect of temperature change will be extremely difficult.

It is possible that, on occasions, the greenhouse effect may be a bigger contributor to changes in global temperature than astronomical factors whilst on others it may not. In some cases it might reinforce astronomic changes. In other words, whilst astronomical changes push the Earth towards an ice age the greenhouse effect may either overwhelm and reverse this trend, make little difference to it, or it may reinforce the tendency to an ice age. If astronomic changes produce changes in the concentration of atmospheric Carbon which reinforce the direction in which astronomic changes are taking place then although increases (or decreases) in Carbon emissions may boost (or decrease) global temperatures it could be argued that the greenhouse effect is just a function of astronomic changes. The theory that the concentration of atmospheric Carbon determines global temperatures does not explain what brought about the change in the concentration of atmospheric Carbon. Once again, proving the relationship between the greenhouse effect and astronomic changes will be extremely difficult.

If there was no such thing as a greenhouse effect on Earth then global temperatures might be colder but not that much colder because the oceans and Forests absorb vast quantities of heat which would continue to keep the Earth warm - even though this heat, once released, would escape back into space more rapidly than it would where a greenhouse effect exists.

It was pointed out above that the quantity of heat absorbed by the top 3 metres of the world’s oceans is greater than that in the atmosphere. This seems to support the argument that the Earth’s global temperature is determined more by the oceans than by the greenhouse effect. Whether it does, however, is not clear for even if the top 3 metres of the oceans contain more heat than the atmosphere this may be due to the infra-red radiation reflected back to Earth by the greenhouse effect rather than because of the direct sunlight absorbed by the oceans so it does not prove that the oceans are a more powerful determinant of global temperatures than the greenhouse effect.

The theory of global warming outlined above would not be seriously damaged by the untenability of the greenhouse effect since it supposes that there are a number of other factors besides CO2 emissions which influence global temperatures and that these causes occur independently of changes in the concnentration of atmospheric Carbon.

Water vapour is a greenhouse gas. The scale of the water vapour released by Forests through evapotranspiration is colossal, “Although only a small fraction of a leaf surface bears the pores through which moisture evaporates, the potential rate of water loss from a many leaved canopy of leaves can approach that of loss from the same area of an open water surface.” (Jonathon Silvertown & Philip Sarre (editors) ‘Environment and Society’ Houghton and Stoughton, London 1990 p.77); “This transpiration (of trees) is a very effective mechanism, and a square kilometre of moist, ‘steamy’ tropical rainforest can push more water vapour into the atmosphere than a square kilometre of ocean.” (Dick File ‘Weather Watch’ Fourth Estate, London 1990 p.253). A square kilometre of trees has a much larger total surface area because of its leaves, than a square kilometre of ocean.

The scale of evapotranspiration’s influence on the formation of clouds, and thus its cooling role in the Planet’s climate, can be appreciated indirectly from the fact that, “Rainfall on the continental land masses of the Earth is, to a considerable extent, a consequence of evapotranspiration; the pumping by trees and large plants of water from the soil to their leaves where it evaporates.” (James Lovelock ‘The Ages of Gaia. A Biography of Our Living Earth’ Oxford University Press 1988 p.90); “Each year approximately 70% of the precipitation which occurs in the (Amazon) tropical forests returns to the atmosphere due to the forests own contribution to the process of evaporation.” (Worldwide Fund for Nature Special Report no.6 May 1991 p.13).

It is possible to argue, without being able to confirm such speculation, that Forests are one of the most important ecological phenomena influencing the Planet’s temperature and thus its climate. The albdeo effect of Forests may be secondary to that of the oceans’ but it is greater than that produced by ice sheets, glaciers, and fresh water systems. Although Forests cover a far less extensive area of the Planet than the oceans, they generate more Photosynthetic activity. It might be suspected that the oceans produce vastly more water vapour than Forests but the huge surface area of all the leaves in Forests means that the difference between them is not as great as might be suspected. It can’t be negligible given that, as Lovelock points out, much of the rainfall falling over the land stems from Forests. It could well be then once all of the factors which influence the climate are taken into account that, at the very least, “Forests rival oceans in their influence on the biosphere.” (Kilaparti Ramakrishna & George M Woodwell (eds) ‘World Forests for the Future: Their Use and Conservation’ Yale University Press New Haven 1993 p.xi).

There are then a number of different hypotheses which attempt to explain the Earth’s climate. There is the astronomic theory; the greenhouse effect in which changes in the concentration of atmospheric carbon produce changes in the Earth’s global temperature; the oceanic theory in which the Earth’s climate is determined by the amount of heat absorbed by the Earth’s oceans; the cloud theory in which the climate is determined by the Earth’s cloud cover; and, finally, the Gaian theory. Of all the theories outlined above the gaian theory is by far the most sophisticated.

This is not the first time the Earth has experienced a spate of ice ages, “It used to be thought that there had only been four or five ice ages, and all within the last one or two million years. Now it is clear that ice ages occurred much earlier in the Carboniferous period (between 345-280 million years ago) and the Permian period (between 280-250 million years ago) and that there were many of them, interspersed with warmer interglacials.” (Dick File ‘Weather Watch’ Fourth Estate, London 1990 p.6).

In terms of the Earth’s recent history, these oscillations are rather strange. It is not known why they are happening nor what is preventing the climate from veering off into a runaway ice age or runaway global warming. There are a number of theories. Firstly, some commentators support the astronomical theory of climate change - that these oscillations are caused by changes in the shape of the Earth’s orbit, “Roughly, the ice ages of the past (about 10 in the last million years) correspond to a 100,000 year cycle; the cycle of the change in the Earth’s orbit from elliptical to circular and back again.” (Tim Radford 'The Crisis of Life on Earth. Our Legacy from the Second Millenium. Thorsons Publishing Group 1990. p.143); “The best explanation of the recurring pattern of ice ages is the changing orbital geometry of the earth as it moves around the sun, which alters the balance of heat between the seasons. The key to the ice ages, it turns out, is that when northern hemisphere summers are sufficiently cool, snow that falls in winter on the land at high latitudes does not melt, but stays and gradually builds up into great ice sheets; the process is reinforced because shiny white snow and ice fields reflect away incoming solar heat, keeping the planet cool .. An ice age ends only when the changing astronomical influences bring very hot northern summers, capable of melting the ice ..” (John Gribbin “In the Beginning. The Birth of the Living Universe’ Viking, London 1993 p.129)

Gribbin believes that astronomical changes triggered the greenhouse effect into reinforcing these changes, “How is carbon dioxide removed from the air when the world cools? During an ice age the world is dry. Winds blow the dust from the arid land out over the oceans, where the iron in the dust helps marine organisms to grow. One effect of this is that plankton thrive, absorbing carbon dioxide, turning it into carbonates in their shells, and dropping it onto the sea floor when they die. Another is that marine algae thrive, increasing the cloud cover of the planet - and clouds reflect away some of the heat of the Sun.” (John Gribbin “In the Beginning. The Birth of the Living Universe’ Viking, London 1993 p.130-131). In other words, when astronomical changes push the Earth towards an ice age this increases marine photosynthesis, decreases the concentration of atmospheric Carbon and thus boosts global cooling. Unfortunately, gribbin does not explain why the Earth does not get colder and colder when astronomic changes decrease the concentration of atmospheric Carbon; and he does not explain how astronomic changes which warm the Earth help to boost the greenhouse effect. The major drawback of the astronomical theory though is that since the Earth’s orbit around the sun hasn’t changed for aeons, it does not explain why these climatic oscillations started a mere 5-2 millions years ago.

Secondly, another commentator believes the arrival of ice ages was caused by the rise of the Rocky mountains which disturbed wind and ocean currents. This hypothesis is much better placed to help to explain the more recent ice age oscillations.

Finally, the gaian theory is that ice ages are a means of combatting the sun’s increasing luminosity, “In the last few tens of millions of years the solar output has reached a level where it is becoming increasingly difficult for the CO2 pumping system to operate. To keep cool when the solar output is as high as now requires efficient pumping by the system so that a carbon dioxide level below 200 parts per million is sustained.” (James Lovelock ‘Gaia. The Practical Science of Planetary Medicine’ Gaia Books Ltd, London 1991 p.148). The Earth’s response to increasing solar radiation is to extract more CO2 from the atmosphere thereby decreasing the greenhouse effect. This has happened through the evolution of new Plants which are able to retain more Carbon and also carry out Photosynthesis in conditions where there is less Carbon in the atmosphere, “Although the appearance of trees (in the geological past) may not have altered the overall rate of CO2 deposition, they have increased the efficiency of the process.” (Lawrence E Joseph ‘Gaia. The Growth of an Idea’ Arkana, England 1990 p.133). It is believed that once the level of atmospheric Carbon is reduced even further than is common during the ice ages then Trees will die out.

In contrast to the astronomic theory of climate in which astronomic changes are reinforced by marine biological activity, gaians argue that the astronomical changes are opposed by marine Photosynthesis. In other words, when astronomic changes begin to cool the Earth, marine activity declines in order to boost the level of atmospheric Carbon and decrease cloud cover whilst, at the other extreme, when astronomic changes warm the Earth, marine activity increases to decrease the concentration of atmospheric Carbon and increase cloud cover, “Since the major agents of fluxes between the atmosphere, the terrestrial and oceanic pools of carbon dioxide are living organisms, the astronomical forcing factors must somehow promote or demote organic productivity. The implication is that during ice ages organic productivity was higher than during interglacials ..” (A M Mannion ‘Global Environmental Change. A Natural and Cultural Environmental History’ Longman New York 1991 p.321).

It has been pointed out above that the stability of the Earth’s average temperature over the aeons is a remarkable phenomena. Given the huge, global-wide, changes which humans have inflicted on the Earth since the end of the last ice age it is even more remarkable that there has been so little change in global temperatures. As the ice sheets retreated at the end of the last ice age, the Earth’s landmasses were gradually covered in Forests, “Forests once covered about 90% of the surface of the Earth.” (Herbert Giradet ‘Earthrise. How We Can Heal our Injured Planet?’ Paladin, London 1992 p.12). Some regions, like the Mediterranean, which are now deserts, were once luxurious Forests teeming with a wide array of Wildlife. The scale of global deforestation since this time is extensive, “Over the last 10,000 years, the earth’s mantle of forests and woodland has shrunk by a third as trees were cleared to make way for crops, pasture and cities.” (Sandra Postel and John C Ryan 'Reforming Forestry' in Lester Brown, ed 'State of the World 1991. A Worldwatch Institute Report on Progress Toward a Sustainable Society' Earthscan Publications Ltd, London. 1991. p.74). “Two thousand years ago, the tropical rainforest alone extended over 5 billion acres, covering 12% of the earth's land surface.” (Jeremy Rifkin 'Biosphere Politics. A New Consciousness for a New Century' Harper San Francisco 1991 p.73). The situation now is that, “One third of the Earth’s total land surface is covered by forests, of which 45% or two billion hectares are tropical.” (Worldwide Fund for Nature Special Report no.6 May 1991 p.10); “The planet’s mantle of trees .. (is) .. shrinking by more than 11 million hectares per year.” (Alan P Durning 'Ending Poverty' in 'State of the World 1990' A Worldwatch Institute Report on Progress Towards a Sustainable Planet' Unwin Paperbacks, London 1990 p.187). For the first time in history, it is possible to envisage the eradication of the boreal Forests of Canada and Alaska, as well as the world’s tropical rainforests, “The rate of destruction of tropical forests means that by the end of the century and given current trends, nearly all forests will be gone in India, Thailand, Vietnam, the Philippines, Madagascar, East Africa, West Africa, and central America, and virtually all primary forest will be eliminated in Burma and Ecuador.” (Norman Myers 'Deforestation Rates in the Tropical Forests and their Climatic Implications' Friends of the Earth 1989). It is highly surprising that although the Earth has lost such a vast scale of tropical and temperate Forests, global average temperatures have not varied by more than 1%. This seems to suggest that Forests are not vital for controlling the Planet’s global average temperature.

Humans have had an impact on the local, and, probably, even the global, climate ever since they evolved as a species some two million years ago - which was, by some estimations, around the same time as the start of the Earth’s periodic ice-ages.[3] Since the beginning of the industrial revolution, however, the over-industrialized world has been dumping so much pollution into the atmosphere and deforesting such vast areas of the Earth, they have started to boost global warming, “Global mean surface air temperature has increased 0.3C to 0.6C over the last 100 years, with the five global average warmest years being in the 1980s.” (JT Houghton: GJ Jenkins and JJ Ephraums 'Climate Change. The IPCC Scientific Assessment' Cambridge University Press, Cambridge 1990 p.xii). More recent evidence shows that, “The eight hottest years (globally averaged) in the past century were, in increasing order: 1980, 1989, 1981, 1983, 1987, 1988, 1991, 1990.” (D.H. Meadows, D.L. Meadows & Jorgen Randers 'Beyond the Limits. Global Collapse or a Sustainable Future' Earthscan, London 1992 p.92).[4]

It is suspected that the only reason global average temperatures have not increased much more dramatically in line with the wholesale geophysiological damage caused by over-industrialized oomans is because the Earth may have been heading back into another ice age. Human induced global warming could be offsetting the return of the next ice age .. “global mean surface temperature has increased by 0.3 to 0.6C over the last 100 years. Thus the observed increase could be largely due to this variability; alternatively this variability and other human factors could have offset a still larger human-induced greenhouse warming.” (IPCC 'Climate Change 1992. The Supplementary Report to the IPCC Scientific Assessment' Ed by J T Houghton, B A Callander & S K Varney World Meteorological Organization/United Nations Environment Programme Cambridge University Press, Cambridge 1992 p.5). One commentator goes even further and suspects that the Earth’s climate began slipping back into an ice age during the medieval period but was dragged out of it by the destruction which humans inflict on the Earth during that time, “As Gribbin has pointed out, there is the real possibility that the enhanced greenhouse effect is preventing the onset of the next ice age. It is also pertinent to examine the possibility that it may have already done so. There is widespread evidence for cooling during what is generally recognized as the ‘Little Ice Age’ of the fourteenth to the early 19C. While it is unequivocal is that interglacial environments were characterized by climatic variation .. there is no precedent for cold periods similar to the ‘Little Ice Age’ in earlier interglacial periods.” (A M Mannion ‘Global Environmental Change. A Natural and Cultural Environmental History’ Longman New York 1991 p.321). The impact of the over-industrialized world on the Planet’s global temperature is becoming so overwhelming it is threatening not merely to delay the next ice age but to create the conditions for runaway global warming which could devastate the Planet’s geophysiology.

In conclusion, life, including humans, has always influenced the Earth’s average temperature and thus the climate so what is happening today is no different - except in scale and rapidity - to what has happened throughout most of the Earth’s history. Whether humans had evolved or not, the Earth’s climate would still undergo constant change. If, at the moment, humans ‘lived in harmony with nature’ and minimized their interference of the Planet’s geophysiology then huge ice sheets may already have begun to appear, or would soon start to appear, across the northern continents. It is clear that if the human race wants to survive in perpetuity on Earth then it must prevent the return of an ice age and, far more pertinently, prevent the over-industrialized world from generating a climate like that found on Venus. Humans should aim to maintain climatic stability.