Methane is produced when organic material decomposes in an anaerobic (oxygen-free) environment. Its main natural source is release from wetlands as a result of the decomposition of organic matter. Human activities that produce methane emissions include herding ruminant animals (cattle, sheep, and goats), growing rice, causing leakage during fossil fuel extraction, burning fossil fuels, causing gas to escape from waste landfills, and burning plant material.

Methane in the atmosphere chemically decomposes and loses its potency as a greenhouse gas in eight to 12 years, so it has a less persistent effect than carbon dioxide. If we significantly reduce our methane emissions, within a decade its effect as a heating agent and producer of lower-atmosphere ozone would be diminished, and a successful longer-term strategy to stop most human-caused methane emissions would take it off the agenda as a greenhouse gas of lasting concern.

Levels of nitrous oxide (known popularly as 'laughing gas') have also increased - they are up by 16 per cent since 1750. While relatively small in concentration, the gas has an effect three hundred times more powerful than carbon dioxide, making its overall contribution to global warming about one-tenth that of carbon dioxide.

The majority of nitrous oxide is emitted naturally from tropical soils and oceans. The human activity that produces most nitrous oxide is agriculture (through the use of fertilisers), but jet engines, some industrial processes, and cars with catalytic converters that burn fossil fuels also contribute to its production. The gas persists in the atmosphere for about 120 years before being broken down by the effect of sunlight; nonetheless, it is slowly acc.u.mulating in the air as a consequence of additional human-caused emissions.

A number of other gases (known as 'trace gases') that are emitted in smaller quant.i.ties from industrial processes - including hydroflourocarbons, sulfur hexafluoride, and perfluorocarbon - contribute to global warming, but on a smaller scale. These gases, together with carbon dioxide, methane, and nitrous oxide, are known as the 'Kyoto gases', because they are defined under the agreement to control emissions that was established by the Kyoto Protocol in 1997.

While human activity since 1750 has raised the carbon dioxide level by 38 per cent to 387 parts per million in 2008, the effect of all the Kyoto gases together is calculated to be equivalent to 455 parts per million of carbon dioxide.

Human activities also contribute to the greenhouse effect by releasing non-gaseous substances such as aerosols, which are small particles that exist in the atmosphere. Aerosols include black-carbon soot, organic carbon, sulphates, nitrates, as well as dust from smoke, manufacturing, windstorms, and other sources.

Aerosols have a net cooling effect because they reduce the amount of sunlight that reaches the ground, and they increase cloud cover. This effect is popularly referred to as 'global dimming', because the overall aerosol impact is to reduce, or dim, the sun's radiation, thus masking some of the effect of the greenhouse gases. This is of little comfort, however, because aerosols, or airborne particle pollution, last only about ten days before being washed out of the atmosphere by rain; so we have to keep putting more into the air to maintain the temporary cooling effect. Unfortunately, the princ.i.p.al source of aerosols is the burning of fossil fuels, which causes a rise in carbon dioxide levels and global warming that lasts for many centuries. The dilemma is that if you cut the aerosols, the globe will experience a pulse of warming as their dimming effect is lost; but if you keep pouring aerosols together with carbon dioxide into the air, you cook the planet even more in the long run.

There has been a necessary effort to reduce emissions from some aerosols because they cause acid rain and other forms of pollution. However, in the short term, this is warming the air as well as making it cleaner.

The total effect of aerosol cooling is generally estimated to be less than 1 degree; however, work by Nicolas Bellouin and a team from the UK Met Office that was published in Nature, in December 2005, found that the cooling effect of aerosols at around 1.4 degrees is much greater than most current climate models estimate. The corollary is that, since aerosols emissions continue to decline, they will be less able to create a cooling effect, and therefore future global warming from greenhouse gases will be greater than presently indicated.

This view is consistent with the idea that climate sensitivity is higher than is generally taken to be the case, as we discussed in Chapter 6. This has led Meinrat Andreae of the Max Planck Inst.i.tute for Chemistry in Mainz, Germany, to conclude that a doubling of pre-industrial carbon dioxide levels by 2100 would produce a 6-degree increase, which would 'be comparable to the temperature change from the previous ice age to the present [and] so far outside the range covered by our experience and scientific understanding that we cannot with any confidence predict the consequences for the Earth'. Andreae's collaborator, Chris Jones, warns: 'Now we are taking our foot off the brake, but we don't know how fast we will go. Because we don't know exactly how strong the aerosol cooling has been, we do not know how strong the greenhouse warming will be.'

While most aerosols act to cool the planet, one component, black carbon, has the opposite effect. Black carbon particles (which are created by burning vegetation; heating with coal; diesel combustion5; and cooking with solid fuels, such as wood and cow dung) act in a similar manner to the greenhouse gases by trapping heat radiating away from the Earth's surface, and by changing the reflective properties of ice-sheets. A study by Scripps Inst.i.tution of Oceanography atmospheric scientist V. Ramanathan and University of Iowa chemical engineer Greg Carmichael has found that soot and other forms of black carbon may have a heating effect greater than any other greenhouse gas, and 60 per cent stronger than that of carbon dioxide. This is three times the effect estimated by the IPCC.

This is good news, in a roundabout way. This discovery means that strong action to cut black-carbon emissions could balance some of the cooling losses that occur when other aerosols produced by burning fossils fuels are reduced.

Together, current levels of greenhouse gases that are caused by human activity are working to produce the following global warming: Long-term effect of the present level of carbon dioxide 1.4C

Plus the effect of non-carbon-dioxide levels of Kyoto gases (methane, etc.) 0.7C

equals the total impact of all Kyoto gases 2.1C

minus thermal inertia (heat being used to warm the oceans) 0.6C

minus the short-term net cooling effect of aerosols 0.7C

equals today's warming 0.8C.

To add another level of complexity, all these estimates are based on a climate sensitivity of 3 degrees for fast feedbacks, which is the middle of the range used by the IPCC. As we saw in Chapter 6, this 3-degree estimate is reasonable in the short term, but there is strong evidence that the figure is double that, at 6 degrees, when all the long-term consequences and slow feedbacks are accounted for.

CHAPTER 9.

Where We Are Headed.

To help think about possible future trajectories of human-produced greenhouse gases, the IPCC has developed six sets of scenarios, each of which makes different a.s.sumptions about future emissions, land use, technologies, and forms of economic development. The scenarios range from those that a.s.sume large reductions in greenhouse-gas emissions to those that a.s.sume a world of 'business as usual' practices and, as such, imagine the most pessimistic, fossil-fuel-intensive emissions future. The current IPCC scenarios were prepared for the panel's 2001 report and are now almost a decade old, lagging well behind reality. As Roger Jones of the CSIRO says, 'At the time of their release in 2000, [the scenarios] were state-of-the-art ... Now, the world is growing faster and is richer than the scenario authors a.s.sumed.'

According to the most recent IPCC report, human-caused carbon dioxide emissions increased 70 per cent between 1970 and 2004, and are rising at an even faster rate now. Their annual increase jumped from an average of just over 1 per cent for the period from 19901999 to more than 3 per cent 83 from 20002004. The actual growth rate of carbon-dioxide emissions since 2000 is greater than growth rates for the most fossil-fuel-intensive of the IPCC emissions scenarios.

A study led by the CSIRO's Michael Raupach, co-chair of the Global Carbon Project, has found that no region is effectively decarbonising its energy supply. Raupach says that a major driver accelerating the growth rate in global emissions is that we're now burning more carbon for every dollar of wealth we create: 'In the last few years, the global use of fossil fuels has actually become less efficient. This adds to pressures from increasing population and wealth.'

In Australia, Raupach says, carbon emissions have grown at about twice the global average during the past 25 years, and have almost doubled the growth rate of emissions in the United States and j.a.pan. He believes that because 'emissions are increasing faster than we thought ... the impacts of climate change will also happen even sooner than expected'.

According to the October 2007 World Bank report Growth and Carbon Dioxide Emissions: how do different countries fare? , Australia increased its carbon dioxide emissions by 38 per cent between 1994 and 2004, to become the sixth-highest per capita emitter (on a base that excludes land use, land-use change, and forestry). Australia's emissions-increase was more than the total of Britain, France, and Germany which, combined, have a population ten times that of Australia.

The rising rate of global carbon dioxide emissions is reflected in a larger annual increase in the level of carbon dioxide in the air. The average increase of 1.5 parts per million for the period from 19702000 has jumped to 2.1 parts per million since 2001. NASA's James Hansen told the Independent in January 2007 that 'if we go another ten years, by 2015, at the current rate of growth of carbon dioxide emissions, which is about 2 per cent per year, the emissions in 2015 will be 35 per cent larger than they were in 2000'. He says that this would take the emissions scenarios necessary to avoid dangerous climate change beyond reach.

Atmospheric carbon dioxide levels are now rising faster than at any time in the past 800,000 years. The level rose 30 parts per million over the past 17 years; yet ice cores drilled in Antarctica show that in the past million years, prior to recent times, the fastest increase of carbon dioxide was 30 parts per million over a period of a thousand years.

The increasing use of energy is also going to increase emission levels. In 2004, the International Energy Agency (IEA) projected that annual carbon dioxide emissions by 2030 would be 63 per cent higher than in 2002. According to the European Union's 2007 World Energy Technology Outlook, 'business as usual' will see global energy use more than double by 2050, with 70 per cent of the increase coming from fossil fuels. The report a.s.sumes that energy efficiency will almost double, in order to support an economy four times larger than today. The result would be a carbon dioxide concentration in the atmosphere of 9001000 parts per million by 2050. It says: 'This value far exceeds what is considered today as an acceptable range for stabilisation of the concentration.' The conclusion is that carbon emissions cuts will come too late to avert 'runaway' climate change if current policy trends continue, and that this would happen despite a 'ma.s.sive' growth in renewable energy after 2030, including rapid deployment of new technologies, such as offsh.o.r.e wind.

While the IEA predicts annual growth in global power consumption of 3.3 per cent per year to 2015, a study by Oxford Economics a.n.a.lysts shows that, when trends in developing countries are studied in more detail, the rate would be even higher, at 5 per cent.

Increasing energy use and rates of greenhouse-gas emissions mean only one thing: it will get hotter, quicker. The IPCC's conservative estimate is a rise of 4 degrees by 2100 for the most pessimistic 'business as usual' scenario, yet our emissions are currently rising faster than this scenario envisages. The ten warmest years on record have all occurred since 1995, and one study predicts a 0.3-degree increase for the period from 20042014 alone.

Before the Arctic big melt of 2007, Hansen and his colleagues, by comparing sea-surface temperatures in the Western Pacific with historical climate data, suggested that this critical ocean region, and probably the planet as a whole, is 'approximately as warm now as at the Holocene maximum [the period of the highest temperature within the last 11,500 years] and within one degree of the maximum temperature of the past million years' [our emphasis]. They conclude that global warming 'of more than one degree, relative to 2000, will const.i.tute "dangerous" climate change as judged from likely effects on sea level and extermination of species'.

Rates of warming since the mid-19th century are higher than those of the last ice age by more than a factor of ten, increasing to a factor of twenty from the mid-1970s. The atmosphere is now heating up more quickly than modern humans have ever experienced. 'We really are in a situation where we don't have an a.n.a.logue in our records,' says Eric Wolff from the British Antarctic Survey. According to Wolff, it is generally accepted that at some stage a 'step change' or 'tipping point' is reached, after which global warming accelerates exponentially. According to new evidence, he says, 'we could expect that tipping point to arrive in ten years' time.' Recent observations from the Arctic, and their implications for the Greenland ice sheet and sea-level rises, suggest that we may have already pa.s.sed that point.

When accepting the WWF Duke of Edinburgh Conservation Medal in November 2006, James Hansen told his audience that the human race must begin to move its energy systems in a fundamentally different direction within about a decade, or 'we will have pushed the planet past a tipping point beyond which it will be impossible to avoid farranging undesirable consequences'. He warned that global warming of 2 to 3 degrees above the present temperature would produce a planet without Arctic sea-ice; a catastrophic sea-level rise of around 25 metres; and a super-drought in the American west, southern Europe, the Middle East, and parts of Africa. Such a scenario, he says, 'threatens even greater calamity, because it could unleash positive feedbacks such as melting of frozen methane in the Arctic, as occurred 55 million years ago, when more than 90 per cent of species on Earth went extinct'.

The ANU's Will Steffen argues that the Earth's climate system 'is highly non-linear and is p.r.o.ne to abrupt changes, threshold effects and irreversible changes' in a human time frame, so that very small changes in a forcing factor 'can trigger surprisingly large and sometimes catastrophic changes in a system ... [and] propel the Earth into a different climatic and environmental state'. Examples he cites include 'the rapid disintegration of the large ice sheets on Greenland and Antarctica or large-scale and uncontrollable feedbacks in the carbon cycle: activation of methane clathrates [frozen water and methane] buried under sediments on the ocean floor, the rapid loss of methane from warmer and drier tundra ecosystems, increasing wildfires in the boreal and tropical zones, the conversion of the Amazon rainforest to a savannah and the release of carbon dioxide from warming soils'. Once we cross critical thresholds and trigger these processes, Steffen says no policy or management approach could slow, or reverse, the process.

Hansen agrees. He says the tipping point occurs when the climate state is close to triggering very strong positive-feedback effects, so that a small perturbation can cause large climate change.

Today, the Arctic sea-ice, the West Antarctic ice sheet, and the Greenland ice sheet can provide such feedbacks. Little additional forcing is needed to trigger these feedbacks, because of the warming that is already in the pipeline. Hansen concludes wryly: 'We have to be smart enough to understand what is happening early on.'

Tony Blair and his Dutch counterpart Jan Peter Balkenende told European leaders in 2006 that, 'without further action, scientists now estimate we may be heading for temperature rises of at least 3 to 4 degrees above pre-industrial levels ... We have a window of only ten to 15 years to avoid crossing catastrophic tipping points. These would have serious consequences for our economic growth prospects, the safety of our people, and the supply of resources - most notably, energy.'

This statement was made before the imminent loss of the Arctic sea-ice, and the consequences of that loss, were as clear as they are today. When that event is taken into account, the ten-to-15-year window looks to be closed already.

CHAPTER 10.

Target 2 Degrees.

Climate change is already dangerous. The signs are evident globally: in the polar north; in Darfur's famine; in Australia's depleted MurrayDarling River system; in the collapse of ecosystems across the globe; in the 2007 mega-fires in Greece and California; in the coral stress in the Caribbean and in Australia's Great Barrier Reef; in widespread species losses; in changing monsoon patterns; in the destruction of lowlying communities; and in regional food-production stress. Our world is already at the point of failing to cope. The UN's emergency relief coordinator, Sir John Holmes, warned that 12 of the 13 major relief operations in 2007 were climate related, and that this amounted to a climate-change 'mega disaster'.

Global warming is now close to 1 degree. Many of the results that were forecast are already coming true.

At a warming of just 1 degree over pre-industrial levels, it was predicted that the Amazon would be drying, and increasingly drought and fire affected. During the 2005 drought, some tributaries ran dry; in 1998, forest fires generated by El Nino conditions poured almost half a billion tonnes of carbon into the air - more than 5 per cent of global greenhouse-gas emissions for that year. The Amazon, responsible for more than 10 per cent of the world's terrestrial photosynthesis, is currently near its critical-resiliency threshold.

In the US, it was expected that a 1-degree rise would result in California and the Great Plains states becoming subject to mega-droughts and desertification: a new and permanent 'dust bowl', similar to those seen between 1000 and 1300 AD during the Medieval Warm Period, when devastating, epic droughts. .h.i.t the plains, and whole Native American populations collapsed. This predicted drying is also occurring.

At a warming of just 1 degree, the North Queensland Wet Tropics rainforest will be an environmental catastrophe waiting to happen, according to Steve Williams, a James Cook University senior research fellow. Just 1 degree is likely to reduce the area of this World-Heritage-listed Queensland highland rainforest by half. As predicted, the Barrier Reef is already subject to regular bleaching (loss of colour due to loss of algae), and is now facing extinction: a survey showed that 6095 per cent of it was bleached in 2002. This is the case with most coral reefs around the world.

At 1 degree of warming, it was also expected that world cyclones would be more severe, and that small island states would be abandoned as seas rose. This is happening.

As predicted for a 1-degree rise, ice sheets around the world are suffering severe losses; and as permafrost melts, landslides in the European Alps are already becoming serious. The Mount Kilimanjaro ice cap, which has been intact for at least 11,000 years, is well on the way to disappearing, with an 80 per cent loss in the last hundred years, and the rest predicted to be gone between 2015 and 2020 as surrounding forests die off.

Britain's Hadley Centre calculated that warming of just 1 degree would eliminate fresh water from a third of the world's land surface by 2100, worsening a water crisis that seems already to be a permanent new part of life in many parts of the world.

All of these effects have occurred with a 1-degree warming; yet the most commonly used definition of dangerous climate change is linked to a 2-degree warming threshold, and its corollary, suggested by Sir Nicholas Stern, among others, that our target should be for a 60 per cent reduction in greenhouse-gas emissions by 2050.

It is important to understand how these numbers achieved such prominence in the climate debate. The first goal set by a forum of international significance was in 1988. The International Conference of the Changing Atmosphere in Toronto advocated a 20 per cent reduction of 1988 carbon dioxide levels by 2005.

In 1990, the first IPCC Scientific a.s.sessment Report pointed out - for educational rather than policy purposes - that it would require a 6080 per cent cut in emissions if carbon dioxide emissions were to be stabilised at the then-current level of around 350 parts per million. This guesstimate was superseded four years later when CSIRO scientist Ian Enting and his colleagues reported the results of ten world climate models, eight of which showed that the reductions required to stabilise the atmosphere at 350 parts per million of carbon dioxide would likely be more than 100 per cent - that is, carbon dioxide emissions would need to be completely eliminated, and carbon would need to be taken out of the air, for 5090 years.

By 1997, however, governments were not thinking of cuts on anything like this scale. This was reflected in the Kyoto Protocol's target for developed-country emissions to be only 5 per cent less than the 1990 level by 2012. Achieving this target would result in annual additions of carbon dioxide to the atmosphere of around of 6 billion tonnes, which would not stabilise greenhouse gases in the air for hundreds of years, and would likely see the level of carbon dioxide climb past 1000 parts per million - more than three times the highest level known in the last million years.

In 2000, realising that the Kyoto cuts were inadequate, Britain's Royal Commission on Environmental Pollution recommended that if greenhouse gases were to be stabilised at 550 parts per million carbon dioxide equivalent, emissions from Kyoto Annex I [developed] nations would need to be reduced to 60 per cent below 1998 levels by 2050. It was argued that this target was needed if the world was to avoid a 2-degree warming. Six years later, however, the Stern Review published data indicating that if the atmosphere was stabilised at 550 parts per million carbon dioxide equivalent, there would be a 99 per cent chance of exceeding a 2-degree warming; so the 2-degree target was then shifted to be a.s.sociated with an emissions cap of 450 parts per million. To stabilise the atmosphere at 450 parts per million of carbon dioxide equivalent, a reduction in emissions to at least 80 per cent less than the level in 1990 is required; yet the target of 60 per cent by 2050 remained a popular government policy long after it was shown to be inadequate.

If we accept that the present rise of 0.8 degrees (with more warming in the pipeline) is already dangerous, we can no longer a.s.sume that we have another 40 years in which to reduce emissions to 6080 per cent below 1990 levels, as argued by those advocating a higher temperature cap of 2 degrees. Nevertheless, it is worth looking at the proposed emission scenarios - the scale and speed of emission reductions - necessary to achieve a 2-degree target, because they demonstrate that even this inadequate target will not be achieved by governments acting in their 'business as usual' mode.

The European Union, the IPCC, and the International Climate Change Taskforce, among many others, propose a temperature cap of 2 degrees to avoid 'dangerous anthropogenic interference with the climate system'. For a 2-degree cap, research finds that, in the long run, the Kyoto-defined greenhouse gases need to drop below 400 parts per million, and they need to be significantly less if the risk of overshooting the target is to be low.

Malte Meinshausen of the Potsdam Inst.i.tute for Climate Impact Research in Germany calculates: 'Our current knowledge about the climate systems suggests that only stabilization around or below 400 parts per million carbon dioxide equivalence will likely [85 per cent probability] allow us to keep global mean temperature levels below 2 degrees in the long term.'

Similarly, Simon Rettalack of the Inst.i.tute for Public Policy Research in the UK says that to have an 80 per cent chance of keeping global average warming below 2 degrees, 'greenhousegas concentrations would need to be prevented from exceeding 450500 parts per million carbon dioxide equivalent in the next 50 years and thereafter should rapidly be reduced to about 400 parts per million carbon dioxide equivalent'.

Compared to 'business as usual' scenarios, 2-degree scenarios are characterised by a very sharp turnaround in emissions - falling to, or below, half of the 1990 level by 2050 - and then declining towards zero. The downward-sloping curves are so steep that they can only be called crash programs.

There are large uncertainties about the relationship between the level of greenhouse gases in the atmosphere and the long-term temperatures that will accompany them. This necessitates the expression of ranges, or probabilities, of outcomes. The Stern Review, using calculations by the Hadley Centre in the UK, shows that, in the long term, greenhouse-gas levels of 400 parts per million carbon dioxide equivalent have a 33 per cent probability of exceeding 2 degrees; a 3 per cent chance of pa.s.sing 3 degrees; and a 1 per cent chance of exceeding 4 degrees.

Because today's carbon dioxide level alone is close to the long-term cap of 400 parts per million of carbon dioxide equivalent and emissions are still rising, the 2-degree strategies depend on 'peak and decline'. This means that the maximum target is breached, but because of the time lag between the increase in greenhouse-gas concentrations and the increase in temperature, there is an opportunity to lower emissions and have greenhouse gases drawn down by the carbon cycle before the theoretical maximum temperature is reached.

Meinshausen describes the process: Fortunately, the fact that we are most likely to cross 400ppm [parts per million] CO2eq [carbon dioxide equivalent] level in the near-term, does not mean that our goal to stay below 2C is unachievable. If global concentration levels peak this century and are brought back to lower levels again, like 400ppm, the climate system's inertia would help us to stay below 2C. It's a bit like cranking up the control b.u.t.ton of a kitchen's oven to 220C (the greenhouse gas concentrations here being the control b.u.t.ton). Provided that we are lowering the control b.u.t.ton fast enough again, the actual temperature in the oven will never reach 220C.

For a 7090 per cent chance of staying below 2 degrees, Meinshausen maps an 'initial peak at 475 parts per million carbon dioxide equivalent', leading to the long-term return to '400 parts per million carbon dioxide equivalent'.

'Peak and decline' a.s.sumes that emissions will eventually be cut to below the Earth's net carbon-sink capacity; it a.s.sumes that there is a mechanism operating to remove the excess carbon dioxide from the air to lower the level of greenhouse gases from the peak, before their full force is felt. But if the weakening of the carbon sinks, as predicted and observed, is sufficiently large, this drawdown effect will not be strong enough. In this case, unless the natural carbon sinks are supplemented by a human-organised carbon dioxide drawdown of atmospheric carbon on a huge scale, 'peak and decline' will be a failed strategy, and atmospheric greenhouse gases will be stranded at a far higher level than planned.

A number of researchers have attempted to estimate the level that emissions would need to be cut to stabilise at a 2-degree rise with a carbon dioxide equivalent of 400 parts per million. Research by Paul Baer and Michael Mastrandrea found that global emissions of carbon dioxide would need to peak between 2010 and 2013; achieve a maximum annual rate of decline of 45 per cent some time between 2015 and 2020; and fall to about 7080 per cent below 1990 levels by the middle of the century. At the same time, similarly stringent reductions in the other greenhouse gases would need to occur.

Meinshausen says: 'To avoid a likely global warming of more than 2C and all its consequences, global emissions would need to be reduced significantly, i.e. around 50 per cent by 2050. Per-capita greenhouse-gas emissions would need to be reduced by around 70 per cent, so that global emissions could be halved despite the globally increasing population.'

Using mid-range climate sensitivity, a team led by the Center for International Climate and Environmental Research's Nathan Rive found that even getting to a 50 per cent chance of preventing more than 2 degrees of warming would require a global cut of 80 per cent by 2050, if total emissions were to peak in 2025. For a lower risk of failure than 50 per cent, the emission cuts would need to be substantially higher.

Now comes the crunch for Australia. Because Australian emissions are five times the global average, and the world population will be half as large again by 2050, these scenarios require Australian per-capita emissions to be cut by at least 95 per cent by 2050 - a proposition currently rejected by Australia's Rudd government.

But how worthwhile will those cuts be, in any case, if 2 degrees is too much? A rise of 2 degrees over pre-industrial temperatures will initiate climate feedbacks in the oceans, on ice-sheets, and on the tundra, taking the Earth well past significant tipping points. As we have seen, likely impacts include large-scale disintegration of the Greenland and West Antarctic ice-sheet; the extinction of an estimated 15 40 per cent of plant and animal species; dangerous ocean acidification; significant tundra loss; increasing methane release; initiation of substantial soil and ocean carbon-cycle feedbacks; and widespread drought and desertification in Africa, Australia, Mediterranean Europe, and the western USA. At 2 degrees, Europe is likely to be hit by heatwaves every second year, much like the one in 2003 that killed up to 35,000 people, caused US$12 billion of crop losses, reduced glacier ma.s.s, and resulted in a 30 per cent drop in plant growth that added half a billion tonnes of carbon to the atmosphere.

At 2 degrees of warming, the summer monsoons in northern China will fail, and agricultural production will fall in India's north as forests die back and national production falls. Flooding in Bangladesh will worsen as monsoons strengthen and sea levels rise. In the Andes, glacial loss will reach 40 60 per cent by 2050, reducing summer run-off and causing horrendous water shortages in South American nations. At 2 degrees, California will see a decline in the snowpack of one-third to three-quarters, with a loss of up to 70 per cent in the Northern Rockies, which will devastate regional agriculture as melt run-off declines. Changing climate will have a severe impact on world food supplies: in central and South America, maize losses are projected for all nations but two. In 29 African countries, crop failure and hunger are likely to increase.

After a careful rea.s.sessment of climate sensitivity and the climate history data, James Hansen and seven co-authors are now suggesting that the tipping point for the presence, or absence, of any substantial ice-sheets on Earth seems to be at around 425 parts per million (plus or minus 75 parts per million) of carbon dioxide. This means that the carbon dioxide levels often a.s.sociated with a 2-degree temperature rise may also be the tipping point for the total loss of all ice sheets on the planet, with an eventual sea-level rise of 70 metres.

Despite the catastrophic consequences of a 2-degree warming, the European Union and the International Climate Change Taskforce, among many others, have set 2 degrees as the target towards which the world should aspire.

But if 2 degrees spells disaster, what will the new 'business as usual' target of 3 degrees bring?

CHAPTER 11.

Getting the Third Degree.

The rapid Arctic melt consigns the widely advocated 2-degree-warming cap - always an unacceptable political compromise - to the policy dustbin. Scientific evidence shows it is too high and would be a death sentence for billions of people and millions of species.

In late 2007, Australian government advisor and former chief of CSIRO Atmospheric Research Graeme Pearman wrote: The global climate-science community has indicated that changes of planetary temperature of even one-to-two degrees have the potential to bring about significant global exposures to coastal erosion, sea-level rise, water supply and extreme climatic events, to name but a few. The potential number of humans impacted by a 2-degree change may count in the hundreds of millions. The European Union has already set a target of maximum warming of 2 degrees in the belief that warming beyond this represents an unreasonable risk of 'dangerous' climate change. Such a change in the average global temperature might be regarded by many as small, but it has the capacity to culminate in major consequences, something that scientists feel is still under-appreciated in both public and private policy development.

Despite the dangerous consequences of 2 degrees of warming, we are now being asked by politicians to consider a 3-degree warming cap, because they consider the 2-degree target to be too great a challenge for their 'business as usual' mode of operation.

Thanks to recent developments in paleoclimatology, we have some insights into what a 3-degree world might be like. In the Pliocene, three million years ago, temperatures were 3 degrees higher than our pre-industrial levels. In that era, the northern hemisphere was free of glaciers and ice sheets, beech trees grew in the Transantarctic Mountains, sea levels were 25 metres higher than they are today, and atmospheric carbon dioxide levels were 360400 parts per million, very similar to today. There are also strong indications that, during the Pliocene, permanent El Nino conditions prevailed. Rapid warming today is already heating up the western Pacific Ocean, a basis for a coming period of 'super El Nino'.

At 23 degrees of warming above pre-industrial levels, and perhaps at much lower warming levels than that, the Amazon rainforest will also suffer devastating damage: its plants, which produce 10 per cent of the world's terrestrial photosynthesis, have no evolved resistance to fire, and the warming may result in it becoming savannah. Further, the carbon released by the forests' destruction will be joined by carbon release from the world's warming soils. This will boost global temperatures by 1.5 degrees, on top of the warming of around 4 degrees by 2100 that is projected to occur if we keep to the current fossilfuel intensive path.

The climate-change model at the UK's Hadley Centre predicts that the chances of an Amazon forest drought would rise from 5 per cent now, to 50 per cent by 2030, and to 90 per cent by 2100. Four or five consecutive years of drought would probably dry out areas of the Amazon sufficiently for wildfires to destroy much of it.