Part 3 (1/2)
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.