An abridged version of this piece has been published in Le Monde diplomatique.
Unprecedented heatwave in Russia, leading to uncontrollable wildfires. Floods in Pakistan the like of which have not been seen in centuries. The breaking up of the Greenland ice-sheet. The coincidence and severity of such natural disasters in recent months has prompted renewed debate about the role of global warming, and whether such crises are merely a foretaste of things to come.
Scientists emphasise that there is no hard data directly linking these recent disasters to specific changes in the earth's climate due to human interference. But they also warn that such crises fit unnervingly well into scientific projections that higher global average temperatures will increase the frequency of extreme weather events worldwide.
So while we cannot be absolutely certain that recent events are due solely or mostly to global warming, we can be sure that if we continue our relentless dependence on fossil fuels, these sorts of extreme weather events will become more frequent, more intense, and more disruptive.
Already, global warming has exacerbated droughts and led to declines in agricultural productivity over the last decade, including a 10-20 per cent drop in rice yields. The percentage of land stricken by drought doubled from 15 to 30 per cent between 1975 and 2000. If trends continue, by 2025, 1.8 billion people would be living in regions of water-scarcity, and two-thirds of the world population could be subject to water stress. By 2050, scientists project that world crop yields could fall as much as 20-40 per cent.
Unfortunately, our window of opportunity to turn things around is closing fast. Global average temperatures have already risen by 0.7C in the last 130 years. In 2007, the UN Intergovernment Panel on Climate Change (IPCC) told the world that at current rates of increase of fossil fuel emissions, we were heading toward a rise in global average temperatures of around 6C by the end of this century leading to "mass extinctions" on a virtually uninhabitable planet.
But things are getting worse, even faster than we had previously imagined. Currently, governments talk about stabilising global average temperatures below 2C, at an atmospheric concentration of greenhouse gases at 450 parts per million (ppm). But according to Dr. James Hansen, head of the NASA Goddard Institute for Space Studies, the upper limit for a safe climate is far lower, at around 350 parts per million (ppm). If we go beyond this for a prolonged period, we would trigger a global average temperature rise of over 1C, whose results, says Hansen, would be "guaranteed disaster."
The problem is that even the 350 ppm limit could be far too conservative. Professor John Schellnhuber, Director of the Potsdam Institute for Climate Impact Research and a coordinating lead author for the IPCC's Third Assessment Report, warns that a safe level of emissions is well below 330 ppm more likely between 280 and 300 ppm.
With the earth already beyond 300 ppm, we are now heading for a minimum rise of 2C this century, if not worse. Many scientists concede that without drastic emissions reductions, we are on the path toward a 4C rise as early as mid-century, with catastrophic consequences. Worse, scientists at Lawrence Berkeley National Laboratory and the University of California at Berkeley now project that at current rates of fossil fuel emissions, we are on course to reach global temperatures of up to 8C within 90 years even worse than the IPCC's worst-scale apocalyptic scenario.
They account for the effects of "positive-feedbacks' not factored in to previous studies that is, the fact that the collapse of any one of these ecosystem hotspots could have a domino effect on the whole earth climate system. Global warming impacts in one ecosystem could feedback into other ecosystems, with the danger of tipping the climate over into a process of exponential, runaway warming. These "positive-feedbacks' mean that as temperatures rise, the capacity of the earth to naturally absorb human fossil emissions increases, multiplying the warming effect.
Thus, without drastically dropping carbon emissions to zero by 2020, we are in danger of triggering dangerous climatic changes that could lead to the irreversible collapses of key interdependent ecosystems, including the loss of the world's coral reefs; the disappearance of major mountain glaciers; the total loss of the Arctic summer sea-ice, most of the Greenland ice-sheet and the break-up of West Antarctica; acidification and overheating of the oceans; the collapse of the Amazon rainforest; and the loss of Arctic permafrost; to name just a few.
For instance, global warming has already accelerated the melt of Arctic permafrost, releasing methane into the atmosphere. Methane is twenty times more powerful as a greenhouse gas than CO2. Above 1C, this process of melting and methane release would be further accelerated, raising temperatures higher, thus releasing more methane, and so on, in an escalating cycle. According to former US Energy Department geologist John Atcheson, "Once triggered, this cycle could result in runaway global warming the likes of which even the most pessimistic doomsayers aren't talking about. If we trigger this runaway release of methane, there's no turning back. No do-overs. Once it starts, it's likely to play out all the way."
Other examples abound. At higher temperatures, plant matter in the soil breaks down faster, releasing stores of carbon into the atmosphere, again multiplying warming, and so on. There is some 300 times as much carbon trapped in the soils as is released each year from burning fossil fuels. Warming is also endangering the tropical forests of the Amazon, the Congo and Borneo, due to decreased rainfall. This is already leading to the collapse of trees, causing them to release their stored carbon. The Amazon alone contains 90 billion tonnes of carbon, enough to increase the rate of warming by 50 per cent. Scientist Daniel Nepstad projects that the combination of warming, deforestation, logging and fires could reduce the Amazon by 55 per cent by 2030, which alone could raise temperatures by another 1.5C.
One of the most disturbing developments is in the Arctic, where summer sea-ice is rapidly disappearing year-on-year. Among other effects, freshwater from the ice-melt as well as increased regional rain and snow (as ice cover retreats, more moisture from the ocean surface evaporates) could dump enough freshwater into the North Atlantic to interfere with and perhaps even stop the Gulf Stream, a strong ocean current which brings warmth to Western Europe. Scientists have warned that the Arctic could see an ice-free summer as early as 2012.
The slow-down or collapse of the Gulf Stream would kick-start abrupt, dangerous and irreversible climate changes, leading to drastic cooling in North America and Western Europe, and frequent droughts in food-basket regions. According to Michael Schlesinger, Professor of Atmospheric Sciences at the University of Illinois at Urbana-Champaign, "Absent any climate policy, scientists have found a 70 percent chance of shutting down the thermohaline circulation in the North Atlantic Ocean over the next 200 years, with a 45 percent probability of this occurring in this century."
Most disturbingly, the environmental disaster stoked by the BP oil spill in the Gulf of Mexico may have amplified this probability. Dr. Gianluigi Zangari, a theoretical physicist at the Frascati National Laboratory (LNF) in Italy, has analysed satellite data-maps from May-June, which confirm "for the first time direct evidence of the rapid breaking of the Loop Current, a warm ocean current, crucial part of the Gulf Stream", in an area adjacent to BP's Deepwater Horizon platform. Zangari concludes that it is "plausible to correlate the breaking of the Loop Current with the biochemical and physical action of the BP Oil Spill on the Gulf Stream", which may "generate a chain reaction of unpredictable critical phenomena and instabilities" in the global climate.