Almost universally, governments are refusing to recognise the scope and urgency of the changes demanded by global warming. The menace, however, is real, and the time available for concerted action to combat it is frighteningly brief.
There is something counter-intuitive here, when most of us are still experiencing climate change only as near-imperceptible shifts in average temperatures. But nature is gradualist only up to a point. The smooth curves that describe "linear" processes can suddenly turn jagged.
Startling new phenomena emerge, often with bewildering abruptness. At certain points, even small quantitative changes can become huge changes of quality. If ocean water heats up beyond 27.7̊C, the weather systems that form over it can include not just local storms, but hurricanes hundreds of kilometres across.
This is non-linear change, in which gradual processes push elements of the material world past natural "tipping points" or "trigger mechanisms", after which new and unfamiliar processes take over.
The Earth's climate, especially if viewed over long periods, is full of non-linear processes. Renowned climate scientist James Hansen, director of NASA's Goddard Space Research Institute, speaks of the Earth being "whipsawed between climate states" as the amount of energy entering and leaving the atmosphere undergoes seemingly minor shifts — in the language of climate science, "forcings".
The Earth's climate, Hansen observes, is "remarkably sensitive to global forcings". This, he explains, is because of a predominance of "positive feedbacks". Gradual warming or cooling brings natural systems to the point where new processes cut in and multiply an earlier trend. Climate change then becomes self-accelerating.
The human-induced rise in global temperatures due to the burning of fossil fuels is an exceptionally large forcing, much stronger than the changes that set off and ended the ice ages of the past million years or so. Over a few decades, the burning of fossil fuels promises to thrust the Earth's biosphere past a series of tipping points, into a climate state hotter than any since modern human beings evolved.
The term "albedo" refers to the propensity of the Earth's surface to reflect radiation from the sun back out into space. Ice and snow reflect about 80% of the sun's heat, while for open ocean the figure can be as little as 10%.
Even minor shifts in global temperatures can produce marked changes in the extent of snow-covered ground and sea ice. These changes then multiply or reduce the amount of the sun's radiation that remains to heat the Earth. Repeatedly in the past, dramatic changes in albedo — referred to as albedo flip — have been crucial for helping to transform slight changes in the Earth's orbit and angle of rotation into ice ages and interglacial warm periods.
During 2007, the world's climate scientists came to realise that albedo flip was underway again. The area of sea ice in the Arctic Ocean during the northern summer was nearly 23% smaller than the previous record. Moreover, this ice was unusually thin; NASA satellite data indicated that the volume of the ice at the end of the summer was just half what it had been four years earlier. Surface temperatures in the Arctic Ocean were the highest on record, in some places 4.5̊C above normal.
Scientists studying the icecaps of Greenland and West Antarctica — to the south of South America — were making analogous findings. Melting was found to be accelerating at alarming rates. Instead of lying thousands of years in the future, Hansen warned, the disintegration of these icecaps might be a prospect for the end of the century.
The warming of the Arctic Ocean has affected nearby land masses, with recent annual temperatures in northern and western Siberia as much as 3̊C above average. Snow cover comes later and departs sooner. Capturing large additional amounts of heat from the sun, the albedo flip threatens to act as a trigger for other non-linear warming processes. The materials for a number of such processes are on hand in the form of vast quantities of carbon contained in Arctic and sub-Arctic peat bogs.
According to researcher Chris Freeman of the University of Wales, a third of the carbon stored on land — a quantity approaching the entire amount of carbon in the atmosphere — is locked up in peat — that is, partly decomposed vegetable matter prevented by low temperatures and acidic conditions from decaying fully. Another estimate, quoted by the New Scientist in 2004, calculates that the bogs of Europe, Siberia and North America hold the equivalent of 70 years of global industrial emissions.
Now, warmer temperatures mean that this carbon is starting to return to the atmosphere.
Warmer conditions in the Arctic are bringing about the widespread melting during summer of permafrost — that is, once-permanently frozen soil and swamps, frequently containing large amounts of peat. Countless new thaw lakes have appeared, and from the lake margins ominous quantities of greenhouse gases are now bubbling, as the peat begins to break down.
The decay of peat follows a range of chemical pathways. In oxygen-poor conditions, anaerobic bacteria produce the gas methane (CH4). Studying thaw lakes in northern Siberia, the journal Nature reported in September 2006, researchers from the University of Alaska found that methane flux from thaw lakes was as much as five times higher than previously estimated.
Much of the methane was ancient, formed during previous warm periods and stored as bubbles in permafrost for scores of thousands of years. The exceptionally rapid warming of recent times thus promises to release far more methane than would be created by the year-on-year breakdown of plant matter.
Methane in the atmosphere is relatively short-lived, persisting for only a few decades compared with several hundred years for carbon dioxide. But while methane is present, its greenhouse impact exceeds that of carbon dioxide by at least 20 times. A massive burst of methane in coming decades could sharply accelerate global warming, and act as a trigger for other non-linear processes.
Carbon from peat bogs enters the atmosphere as carbon dioxide as well as methane. If the bogs dry out in warm weather, the peat readily combines with oxygen from the air. On occasion, it even catches fire.
Even if the peat remains saturated, the conditions of the new era of climate change are well able to turn it into carbon dioxide. According to New Scientist in 2004, researchers have found that quantities of dissolved organic carbon (DOC) are rising at as much as 6% per year in rivers that flow through peatlands. Once the DOC is in the rivers, bacteria rapidly convert it into carbon dioxide that bubbles to the surface.
The melting of Arctic permafrost will dramatically increase the area of peatlands where this effect applies. Once the bogs have melted, research by Chris Freeman indicates, the main reason for the growing DOC levels is not so much higher temperatures as the increased amounts of carbon dioxide and nitrogen compounds already in the atmosphere. Accumulating in the soil moisture, these appear to feed bacteria that break down the peat. "The peat bogs are going into solution", New Scientist remarked.
By the middle of the century, Freeman told New Scientist, DOC emissions from peat bogs and rivers could be as big a source of atmospheric carbon dioxide as the burning of fossil fuels.
Despoiling the forests
Lesser but still perilous amounts of carbon seem destined to enter the atmosphere through the effects of deforestation. Brazil and Indonesia are among the top four greenhouse polluters, primarily because of the logging and burning of their forests. According to the London Independent in January, one-fifth of the Amazon basin has been stripped of its trees in recent years. In December, the World Wildlife Fund published research suggesting the Amazon forests could disappear by 2030.
Even where the chainsaws have not penetrated, forests can suffer drastically if there is widespread logging in nearby regions. Cleared rainforests regenerate slowly at best, and soil degradation often makes their regrowth impossible. The savannas or crop culture that mostly succeed the forests allow far more sunlight to reach the earth, resulting in higher regional air temperatures and lower humidity. Droughts become more frequent, and in the drier conditions forests become susceptible to burning. Rainforest plants are ill-adapted to fire, and are quickly killed. With the foliage gone, temperatures rise, and yet more forest dries out.
What the loggers have begun, global warming seems set to exacerbate. Quite independently of human assaults on the rainforest, modelling of rainfall in the future greenhouse world indicates a trend to drier conditions both in the eastern Amazon, and with more frequent El Nino events, in Indonesia. A paper in 2000 by the Hadley Centre of the British Meteorological Office speaks of the near-total collapse of the Amazon rainforest unless global temperature rises are kept to the now-difficult level of 2̊C. Models describe an Amazon climate in 2100 with almost no rainfall, and average temperatures of 38̊C.
According to British writer George Monbiot in his 2006 book Heat, the Amazon basin alone has the potential to release 730 million tonnes of carbon per year, about 10% of today's human-induced emissions, for the next 75 years.
While the ravaging of the Earth's tropical forests promises to be the first, most visible catastrophe of the era of global warming, a climate disaster of even greater scope could be developing in the soil beneath our feet.
Scientists have known for many years that with extra carbon dioxide, plants grow more vigorously. In six years of experiments in Florida, a Northern Arizona University team hoped to find that the amounts of carbon fixed in soils would increase as well.
The reverse turned out to be true. Reporting in 2007, the researchers explained that as carbon dioxide levels in the air increased, soil carbon was actually lost back into the atmosphere. The reason, the scientists concluded, was increased activity by soil fungi.
Observations from nature confirmed the experimental findings. In 2005 the British Guardian reported that a 25-year study of soils in England and Wales had discovered carbon losses "consistently, everywhere … and therefore probably everywhere in the temperate world". The richer the soils, the scientists observed, the higher the rate of loss.
The carbon contained in English and Welsh soils was migrating to the atmosphere, the scientists calculated, at an average rate of 0.6% per year. Across Britain, the extra carbon dioxide was enough to cancel out all the emissions savings Britain was due to make under its Kyoto Protocol obligations.
Worldwide, the soil carbon reservoir is reckoned at more than double the carbon content of the atmosphere. Without prompt, drastic curbs on fossil fuel emissions, the mobilising of soil carbon could overtake all efforts to restrict global warming.
Of more than 7 billion tonnes of carbon that reaches the atmosphere each year as a result of human activity, the Earth's natural systems absorb about 4 billion tonnes. Obviously, any process that reduces this natural absorption adds to global warming. The clearing of forests represents a major reduction in the Earth's carbon "sinks".
Now another such reduction, also massive, has been identified. This involves changes to the chemistry of one of the Earth's oceans.
Historically, the oceans have absorbed about 2 billion tonnes of carbon from the atmosphere each year. But in May 2007, New Scientist reported that the Southern Ocean — previously one of the biggest sinks —, had in effect stopped soaking up carbon dioxide.
For 24 years, scientists at the University of East Anglia in Britain had been monitoring oceanic carbon around the globe. During this time, they found that the Southern Ocean carbon reservoir remained virtually constant.
"This is surprising", researcher Corinne Le Quere told New Scientist, "because during the same time CO2 emissions increased by 40 per cent. As the sources of CO2 go up we would expect the reservoir to increase too."
The explanation appears to relate to the fact that deep ocean water normally contains higher levels of dissolved carbon dioxide than water higher up. Near the surface, vast quantities of tiny organisms use sunlight, along with carbon dioxide absorbed from the air, to carry out photosynthesis. When marine organisms die, their remains sink to lower levels, taking their carbon content with them. In time, this organic matter oxidises and enters solution.
With global warming, the Southern Ocean in recent decades has become noticeably windier. The increased windiness causes additional churning of the waters, bringing water from greater depths to the surface. With it comes the stored carbon, enough to ensure that the net flow of carbon dioxide between the atmosphere and the surface waters is roughly zero.
Gambles we must not allow
Like other non-linear phenomena, changes in the oceanic carbon sink are difficult to quantify and predict. Who yet knows whether, or how fast, the effect seen in the Southern Ocean will develop in other ocean regions? Consequently, the scientists who prepare global climate models have often been reluctant to try to incorporate non-linear effects into their work, at least until more complete data become available.
One result of this reluctance is that "official" climate reports, though often disturbing, have not been nearly as frightening as they ought to be. This is the case with the Fourth Assessment Report of the United Nations Intergovernmental Panel on Climate Change (IPCC), presented late in 2007. This report had a cut-off date for citations of May 2005, meaning that much new evidence on non-linear phenomena was not taken into account at all.
The IPCC's report presents generally conservative findings, hedging them with warnings that the actual reality could turn out to be much worse. Predictably, governments and corporations have cited the IPCC's cautious baseline figures, while essentially ignoring the caveats.
The uncertainties in the science, however, do not permit this irresponsibility. Particular tipping points may turn out to be more remote than expected, and positive feedbacks less potent. But there are many non-linear processes, and we will not be lucky in every case. If governments will not take the lead in preventing disaster, populations must seize the initiative instead, and enforce the transformations required.