The central environmental issue that we face today is that of changes in climate on continental to global scales. It is central because climatic conditions control food production by geographically fixed agriculture, on which all but tiny groups of nomadic gatherer-hunter people depend entirely. Human population has grown to the level of billions in a mere 6-10 thousand years, mainly in the last 200. I say "mere" because the record of conscious, tool-using humans goes back 2.5 million years. For the vast bulk of that time the human population was sustained only by the productivity of natural ecosystems, of which humanity was a very minor part, and its increasing ingenuity. Before ten millennia ago there were never more than a few hundred thousand to a few million living humans.
Increasingly conscious intervention in natural ecosystems exploded after about 10 thousand years ago by the systematic harvesting of abundant grain-bearing plants and the domestication of animals, the selection of different species depending on geographic location. These strategies became possible partly through expanding human consciousness and culture over the preceding 150-250 thousand years, when fully modern humans appeared on the scene. But it was permitted by an expansion in grass-like plants and various herd animals that evolved to graze on them, as the Earth's climate shifted back and forth from glacial to warmer conditions. These grasses are themselves a relatively recent evolutionary development adapted to cold conditions when the carbon dioxide in the atmosphere, on which all plants depend, periodically fell to low amounts.
This new strategy, followed closely by selective breeding, immediately increased the productivity of labour. It allowed population to increase, but also demanded living on fixed areas of fertile land; a fundamental shift from the previously dominant gatherer-hunter strategies that are only possible with seasonal migration. For the first time in the history of the planet a life-form was able to produce food surplus to its immediate needs. It is from this transformation in the relationship between humans and nature that sprang the whole of subsequent history - the establishment of wide trading and the rapid development of class society, through the expropriation of surplus by new ruling elites. The agricultural explosion marked the emergence of capital in its first form. Inevitably, it also saw the start of irreversible transformation of natural ecosystems. Humans, like any other animals, previously had various effects on ecology, but these influences were part of a stable, dynamic balance.
Earlier environmental changes were indeed varied and dramatic, but stemmed entirely from processes involving the circulation of ocean water and air masses, and the heat that they retained, fluctuations in the amount of heat received from the Sun, due in part to astronomical factors, and changes in how much of this heat was retained by the atmosphere because of its content of absorbent gases, primarily carbon dioxide. This gas is continually added to the air by volcanoes, but is the building material, together with water, for all forms of life. As living things grow they draw on carbon dioxide in air. When they die their decomposition returns the gas back to the atmosphere, but a proportion of their remains always fails to break down completely. It is buried by sands and silts eventually to become locked in rock, thereby removing carbon dioxide from the air for immensely long periods. This complex part of the essentially dialectical relationship between inorganic and organic nature governs the fluctuations in climate on all scales and at a bewildering variety of rates.
Earlier human history was a mainly passive response to this shifting balance of global and local forces. In its 2.5 million-year course the Earth had fluctuated between ice ages and intervening warm episodes about 50 times in a remarkably regular sequence of cycles. In response to these changes, and to the shifting of plant and animal communities that they drove, humans had migrated again and again across the planet from their place of origin in eastern Africa. Only the creation of a tool-using culture and spiralling consciousness, through a conflict with prevailing natural forces, enabled these population shifts, unique in the animal world. By 10 thousand years ago every land area outside Antarctica and the islands of the central Pacific Ocean had been permanently colonised. Agricultural economies rose independently on all continents except Australia between 10 - 6 thousand years ago. This coincided with the start of global warming to the general levels that prevail today.
Growing populations, armed with this new culture, spread from the centres of its discovery in the Middle East, parts of Africa, Central America and SE Asia. The culture demanded land cleared of trees and scrub, so beginning the humanisation and eventually the capitalisation of the fertile parts of the continents. The remains of pollen in swamp sediments chart this human transformation of forests to agricultural land. In Europe such peaty layers show a sudden decrease in tree pollen relative to that of grasses and open-land weeds about 6 thousand years ago, coinciding with evidence for the earliest metal-using culture of the Bronze Age.
Thereafter climate did shift, the long warm period of the Middle Ages and the "Little Ice Age" from 1400 to 1850 AD being well documented in contemporary records. The extent to which this minor fluctuation reflected changes associated with the spread of agriculture is not yet understood. The bourgeois social revolutions beginning in the 17th century introduced another entirely new factor into the climatic system that was linked directly to the mechanisation of culture. To power the Industrial Revolution capital was obliged to penetrate the most important part of natural climate regulation by exploiting buried reserves of coal, and then oil and natural gas. Burning these fuels combines the carbon locked in them with oxygen from the atmosphere, to produce carbon dioxide emissions at rates that now begin to match those occurring naturally from volcanoes that tap the Earth's deep interior. These deposits are a legacy from processes that have operated since life first appeared about 4 billion years ago, but which increased rapidly about half a billion years ago on the emergence of organisms larger than a single cell. They are "fossil" fuels that accumulated by burial of partly decomposed organic remains. It is this long history of burial of part of life's productivity that has largely shaped the Earth's climate, by steadily drawing off heat-absorbing carbon dioxide from the atmosphere at a slightly faster rate than it can be replaced by volcanic exhalation from the deep interior. The base of all modern ecosystems is plant life, which alone performs the vital task of converting water and carbon dioxide to carbohydrates, fats and proteins etc., which it achieves by photosynthesis. One of its products is oxygen, which in the absence of life would be unable to exist in its free form but would remain locked in water and rocks. Without the burial of organic remains large, multicelled animals that depend on oxygen could never have emerged from the earlier world of simple bacteria.
Here we need to look in a little more detail at carbon dioxide's role in climate. Along with a few other gases (mainly water vapour and methane), it is able to slow down the loss of heat from the Earth's surface. If it were not present at all in the atmosphere the Earth would have an average surface temperature of about minus 15° Celsius; it would be ice-bound from pole to pole. The more of it there is, the more efficiently the Sun's heat is trapped in the atmosphere. On Venus, where it constitutes over 90 per cent of the atmosphere, the surface temperature is 450°C; sufficient to melt lead. Taken in isolation (and as we shall see, this is grossly misleading), rising levels mean climatic warming and a reduction encourages a drop in global temperatures. The release of carbon dioxide from its long-term storage in rock is currently increasing its atmospheric level at a dramatic rate.
Bourgeois views of the consequences of this focus on warming of climate, and opinion is divided. On the one hand are those who either dismiss global warming as doom-mongering, or claim that it will stave off a return to the kind of glacial conditions that characterised the period before 10 thousand years ago - seemingly inevitable if previous patterns of climatic fluctuation continue. On the other are those who fear the loss of real estate through a rise in sea level brought about by melting of the ice caps of Greenland and Antarctica - the City of London and Wall Street are definitely at risk if that should happen! Although many environmentalists focus on other, more obvious outcomes of the increasing use of fossil fuels - the risk to human health and to ecosystems by emissions of acid gases and the formation of toxic and cancer-inducing photochemical smogs - the role of otherwise innocuous and very rare carbon dioxide in climate destabilisation was first publicised by environmentalists in the late 1960s. Its contribution to the so-called "greenhouse effect" is predictable from quantum theory, but was initially regarded by scientists as just an oddity.
Whatever course it takes, climatic change linked to capital's inexorable dependence on fossil fuels will impact first on agriculture, because it operates in areas determined by soil fertility, and more or less fixed (until recently) rainfall distribution and narrow ranges of seasonal temperature change. Changing cropping patterns on continent-wide scales is measure that is virtually impossible to contemplate, particularly for the subsistence farmers in the "Third World", who constitute well over half the human population. Under present economic conditions it presents a future of chaos, misery and starvation that dwarfs any previous disaster; for billions it means no future in the most literal sense. Already there are signs of quite minor changes in the Earth's heat transfer system that seem responsible for the droughts that have affected eastern and southern Africa over the last 3 decades, in which millions have starved or succumbed to disease.
Socialists stand together with environmentalists in demanding reduction of emissions from fossil fuels for the same reasons. A central feature of any manifesto of the Movement Towards Socialism has to be for a world economy where fossil fuels are replaced by other, renewable and non-emitting energy sources, in which considerable progress has been made by virtually unfunded researchers in the Alternative Technology movements on several continents. However, calls for change and the search for alternatives by an international community of technologists may prove to be insufficient. Recently published research paints a harrowing and entirely unexpected scenario of future climate shifts, based on growing knowledge of the pace, direction and underlying controls of changes in the past.
Research on climates of the past by geologists and oceanographers centres on analysing cores drilled from deep-sea sediments and the ice caps of Greenland and Antarctica, both of which accumulate regularly and continuously over time as a series of recognisable layers. Potentially, events down to the level of a few years can be unravelled, given sufficient funds and trained personnel. For almost 150 years it has been commonly known that glacial conditions advanced and retreated over the last couple of million years, but few details were available outside of the debris left on the continents by the last glacial episode. Since about 20 years ago the sea-floor record has provided a proper time sequence and evidence for shifts in ice cover, sea-level and the migration of minute plants and animals that are sensitive to water temperature. The record is sufficiently detailed to show regular changes. These match almost exactly the fluctuations in the gravity field in the Earth's orbit that Milutin Milankovich, a Serbian astronomer, calculated from planetary motions in the 1930's. The fluctuations perturb the Earth's orbit, the angle of tilt of its rotational axis and the way that it wobbles slowly like a gyroscope. Each of these changes the amount of heat available from the Sun across the surface. Milankovich's painstaking calculations and his suggestion of an astronomical forcing of climate were almost forgotten, since the heat changes are very small, in fact too small to have cooled the world from the steamy warm place that it most certainly was at the time of the dinosaurs, up to about 60 million years ago. The discovery of his signal was surprising, especially as it was so dramatically strong. Some other long-term process had underlain earlier global cooling, almost certainly linked to the slow drift of continents and changes in patterns of oceanic and atmospheric circulation, together with increased extraction of carbon dioxide from the atmosphere. That line of research is not important here, and we focus on the shorter-term record.
In the ice-cap samples, the glacial periods are signified by a drop in the carbon dioxide content of air trapped in the ice. As water cools it can dissolve more gas, so helping animals that secrete carbonate shells to grow in numbers. These shells together with undecayed soft parts are buried, so explaining the carbon dioxide drawdown. Cooling has a self-sustaining aspect. The combination of astronomical and biological controls seemed to provide the answer to the glacial cycles, in particular they help account for the longer duration of glaciations (around 100 thousand years) than intervening warm periods (around 10 thousand years), in one of which we now live. Empirical observation seemed to have settled the issue, except for tidying up the details. However, it is the details that prove to be the undoing of a purely empirical conception of climate.
The latest work by Danish, Dutch and French scientists, reported in the October 1996 issue of the journal Geology, examines in the finest detail yet possible the minor advances and retreats of glaciers in the last 50 thousand years of the last Ice Age. That began about 120 thousand years ago, and reached its most frigid at 20 thousand years before the present. The researchers achieved a time resolution around 100 years, so that previously known fluctuations of the order of 4 to 5 thousand years stand out in sharp detail. Each of these cycles begins with a relatively warm period when the great ice sheets had withdrawn. The record then shows gradual cooling and slow ice advance, only for it to withdraw again for a few hundred years. These minor warming episodes are followed by a rapid descent into full glacial conditions, in less than 100 years. In the most extreme of these advances ice almost a kilometre thick reached the northern outskirts of Greater London. Each frigid episode ends even more rapidly than it began with a dramatic jump in sea-level and temperature, only to approximately repeat the cycle.
The emergence from the depth of the last Ice Age was equally swift around 13 thousand years ago, and warmed conditions encouraged colonisation of northern Europe. But the unfortunate colonists were plunged into nearly full glacial conditions by the last of these climatic hiccups two thousand years later. The 600 year-long mini-icehouse that Britain became saw the spectacular scenery of the Scottish Highlands, the Lake District and North Wales carved by fresh glaciers. It almost certainly arrived with no warning, within a human lifetime.
For the last 10 thousand years the Earth has experienced the warmest climate since 130 thousand years ago, as part of the probably astronomically governed long-term cycling. However, the lesser very abrupt cycles relate to no known external influence, and they are not so regularly revisited on the planet. When first discovered by Danish oceanographers, an explanation by internal regulation was sought. It had to result from some behaviour of the Earth's external heat-transfer system, and this is dominated by ocean currents. All school atlases show these currents, but only those at the surface, easily charted by ships and the spread of dead vegetation, such as the Caribbean coconuts that regularly turn up on Britain's western shores. Another discovery in the last few decades is that these are matched by much deeper flows of water, that connect all the oceans. They seem to be a vital key to climatic events, although their full passage takes around a thousand years. The principle whereby they operate is very simple, though most unusual.
In the same way as you can make powerful liquor from supermarket plonk in your freezer, when the sea freezes in the Arctic and Antarctic oceans the ice is pure water and a concentrated residual liquid remains. In home-brew this is increasingly pure alcohol. With sea water, the residue becomes saltier, denser and colder, because salt, like alcohol, reduces freezing point. The cold brine sinks to flow along the ocean floor away from the poles. In sinking it must be replaced by surface water drawn polewards from the tropics. These surface currents in the Atlantic, mainly the Gulf Stream, warm the shores of northern Europe and keep it warmer than its high latitude might otherwise suggest. It is this process that presently ensures that huge ice caps cannot form on the northern continents - the true signature of an Ice Age, for that on Antarctica is a permanent fixture isolated to a large degree from the rest of the world's climate.
The new research suggests convincingly that despite the cold in a glacial episode, the continental ice sheets melt at their fronts in summers. This pours low-density fresh water into the northern Atlantic. It floats on normal seawater and winter freezing of the sea cannot drive the deep currents. As ice builds on the continents its bright surface reflects away more of the Sun's heat, and a "double lock" sustains glaciation. But partial stagnation of the ocean heat exchanger means that surface water in the tropics becomes warmer and spreads polewards beneath the cold but fresh layer. Eventually it wells to the surface, so rapidly warming the northern climate and forcing the glaciers to retreat. For a while the fresh water provided by this melting back continues to prevent deep circulation and rapid climate fluctuation results until the fresh water is mixed with salt water. This freezes to restore the circulation, suddenly dragging in yet more warm water to give a rapid temperature rise when further melting overwhelms the system with fresh melt water at the surface. Once more the circulation is stopped and the glaciers rapidly expand.
Emergence from the last Ice Age marked an increase in solar heating because of long-term astronomical factors. The mini-Ice Age 11 thousand years ago is now thought with some certainty to have been triggered by glacial melt water, ponded up in the centre of North America by residual ice, suddenly flooding down the St Lawrence into the North Atlantic. This temporarily upset the deep circulation and cut off the recently regenerated Gulf Stream.
If sea ice cannot form because of a warming climate due to fossil fuel burning, the deep currents would stop abruptly too. Contrary to the fears of an increase in temperatures, this would trigger a massive cooling over the northern continents. Here we have a powerful demonstration of the complexity of the environment and its operation according to dialectical laws. The research has perhaps uncovered the mother of all negations as far as human survival is concerned, beyond the ken of the bourgeoisie and towards which capital may be driving us. The present warm, or interglacial period has lasted 10 thousand years - about the same as every preceding, complete interglacial. The deep ice core in Greenland shows that the last interglacial ended in a matter of a few tens of years.
There are further complexities because carbon dioxide dissolves to a greater extent in cold water, and ground-up rock supplied by glaciers "fertilises" upper ocean layers so that planktonic life blooms to draw down yet more of the heat-trapping gas. Research at the degree of precision necessary to fully understand climate controls is a mere 5 years old, and further surprises are undoubtedly in store. Yet all will point unerringly to the destabilising influence of capital in the climatic sphere as well as in the social devastation from its inevitable attempt to drive up the rate of profit.
The possibility that global warming might trigger its opposite, a descent into full Ice Age conditions might seem a cause for concern among those of us living at high northern latitudes, despite our relatively privileged economic position. Although working at a slower pace, scientists examining the record in the tropics during the recent past have discovered an parallel contradiction. "If it get cooler, surely things will improve in, say, Africa. It ought to rain more and the deserts should bloom." That was a widely accepted view only a matter of twenty years ago. Geological research in Africa and South America shows conclusively that the great forests retreated to much smaller refuges during the last Ice Age. The great lakes of central Africa all but dried up. The biggest, Lake Victoria, is only 12 thousand years old in its present form. The lush grasslands of Botswana are rooted in giant sand dunes formed in a much broader Kalahari Desert, as too the southern fringes of the Sahara. The world was not only colder, but very much drier too, for less water evaporated from the oceans to fall as rain over the continents. It was also extremely windy. The fertile soils of western China are dusts blown in giant storms from the unvegetated ice fronts to the east in Scandinavia and northern Russia. Asia was a dust bowl of continental dimensions.
Such arid conditions in the tropics have returned 50 times since conscious, tool-using humans emerged. They are now seen as the primary driving force behind the waves of migration out of Africa that populated the rest of the world, beginning as early as 1.8 million years ago. The ancestors of modern Europeans themselves followed game and food plants northwards, out of Africa at the depth of the last Ice Age. Within 10 thousand years their extra numbers added to earlier populations subsisting at the margin of the great ice sheets depleted stocks of game and plant resources to the extent that their predecessors, the Neanderthals, became extinct. This happened at a time when the total human population in Africa, Europe and Asia was no more than a million people. Today that population is approaching 5 to 6 thousand times that number, two thirds subsisting at the margin of survival in mainly tropical areas.
Drought and famine in Africa today seem increasingly likely to be linked to minor shifts in climate controls, probably the increased magnitude of the fluctuating equatorial current in the Pacific that is behind the periodic El Nino events that clearly encompass the western hemisphere and maybe that in which Africa is situated. The effects of such upheavals in rainfall are worsened by devastation of farmland forced on the African people by the conditions of their meagre lives. Since imperialism entered the African scene in the last 150 years, its demand for cash crops as well as metals and other resources, its refusal to transfer technical know-how and, and more recently its imposition of crippling debt through so-called development loans drive the plight of the poor of Africa ever deeper. The same can be said to a lesser extent of the people of Central and South America and southern Asia. Not only does two thirds of the world's population face no future under capitalism, but neither do people of the imperialist heartlands and of the former Stalinist states, whose environmental devastation is only just beginning to become clear.
In the same month as the dramatic publication of the Ice-Age research, 16 pages of the journal Nature were taken up with research of a positive nature. Although much of the cycling of carbon dioxide takes place through land plants, it is marine life that offers the best chance of exploiting the burial of organic remains to restore some balance to climate. Land-pant debris mainly decays back to atmospheric gases, whereas a proportion of the oceans' bio-productivity sinks with a good chance of long-term burial. In 1993 and 1995 two perhaps historic experiments were carried out in the central Pacific Ocean. This is an area where plankton are rare, despite high nutrient content of the surface waters (mainly nitrogen and phosphorus) - typical of all oceans far from land. The oceanographer, John Martin, now sadly deceased, observed that the critical chemical element in plant-cell metabolism is iron. This is because the pigment chlorophyll at the centre of photosynthetic fixing of carbon dioxide and water in living matter is an iron-based protein. After some laboratory experiments he proposed that it was iron deficiency in the oceans that prevented them from playing a significant role in absorbing carbon dioxide emissions. Iron in solution is supplied to the sea mainly by rivers, whose influence extends no more than a few hundred kilometres offshore. The experiments "seeded" the surface waters in areas around 100 square kilometres with iron sulphate - one of the simplest compounds imaginable and easily available in large tonnages at extremely low cost (there is a glut of both scrap iron and sulphur).
Within a matter of days plankton "bloomed", reaching 20 times their previous concentration. The atmosphere and water in the test areas saw a 60 percent drop in carbon dioxide levels, and the levels of a strange gas, dimethyl sulphide, increased by three times. Dimethyl sulphide gives sea air its distinctive smell, but also has the opposite effect to carbon dioxide. It helps the upper atmosphere more efficiently reflect away incoming solar power, so helping the world to cool. Glaciers pour vast amounts of iron and other nutrients into the oceans, because they grind up rock to a floury consistency that stays suspended for long periods. This ocean "fertilisation" could well be behind the observed decreases in carbon dioxide content of air trapped in Greenland and Antarctic ice during the last Ice Age.
The experiments inspired by John Martin were conducted by 19 marine scientists from the USA, Mexico and Britain, many others freely contributing their talents and resources. By comparison with the potential of the project their budget was of the shoestring variety, as is that of virtually all lines of fundamental research, except for those linked to production of weapons of mass destruction and from which increases in the rate of profit might stem. It stands as a model of selfless international collaboration that must be followed in every strand related to problems stemming from capital's death-grip on the planet and to means for improving the standards of life and prospect of a future for billions of people. Not only must demands be placed on governments and international bodies for diversion of funds to such lines of investigation, but the huge resources of skilled personnel, equipment and profits of multinational oil companies, such as Shell and BP will need to be requisitioned to expand the research and to take well-designed measures to reverse the climatic damage that has already been done. Such a programme cannot be in isolation from the need to end the reliance on fossil fuels by rational energy and transport management, at the centre of which must be research and action on alternative sources of energy, much the most important being that which the planet receives freely from the Sun itself.