On the election night of 7 November 2000, the American public held its breath as a cliffhanger result in Florida produced a near-tie between Republican George W. Bush and Democrat contender Al Gore. A month later, Bush won a legal challenge to stop the statewide manual recount that was underway, effectively sealing the presidency with a narrow margin.

While Bush settled into power, Gore started to travel the country armed with a slideshow, warning about the risks posed by global warming. Last year, his presentation was expanded into An Inconvenient Truth, a compelling documentary film conveying the message that we have only a decade left to act against climate change. There is a growing sense of urgency, with 68 per cent of Australians now believing global warming poses a critical threat to the country’s interests over the coming decade.

Until recently, scientific opinion was divided, but today scientists share a near-unanimous consensus that we are seeing human-created climate effects and, as the data has hardened, former sceptics have been jumping ship. Many of those who remain have links to industry-funded think-tanks.

The warming greenhouse

Carbon dioxide (CO2) is generally considered the greatest contributor to planetary heating. Since the beginning of the Industrial Revolution, atmospheric levels of this gas have shot up from around 280 parts per million (ppm) to 380ppm and are still rising. The picture is further complicated by other natural and human-made greenhouse gases including methane, nitrous oxide, fluorocarbons and sulphur hexafluoride.

James Hansen of NASA has been issuing alerts for the past three decades, while the UK’s Chief Scientific Advisor Sir David King considers climate change to be a greater global threat than terrorism. Leaving aside the more apocalyptic future predictions, the outlook is nevertheless worrying: glaciers are melting across the world; the vanishing Arctic ice pack is threatening the future of the polar bear; and rising tides are eroding the low-lying Pacific island of Tuvalu. In the future, we may see an exodus of millions of environmental refugees from coastal cities.

A few years ago, the Intergovernmental Panel on Climate Change (IPCC) predicted a temperature rise of somewhere between 1.4 and 5.8 degrees by 2100. As nature tends to operate in non-linear ways, among the more insidious climate risks are feedback loops. These mechanisms could cause climate change to spiral out of control in a cycle where increasing temperatures destabilise the natural balance, in turn accelerating greenhouse gas releases. Some feedback cycles appear to have begun already, while others could be triggered by further temperature rises:

• Permafrost has started to melt in tundra regions of Alaska and Siberia, changing them from carbon sinks (net absorbers of CO2) into carbon sources (net emitters).
• Although forests have traditionally been carbon sinks, the balance could easily be tipped by climate-related factors.
• As the Arctic ice cover disappears, the ocean’s reduced albedo (intensity of light reflected back into space) causes the earth to absorb more heat via the Arctic Ocean.

Perhaps indicative of feedback scenarios, some observations from around the world indicate warming is taking place significantly faster than anticipated: last year, Greenland’s ice sheet was estimated to be melting three times faster than in 2004.

The human factor

Most greenhouse emissions can be traced back to the burning of fossil fuels, particularly oil and coal. More indirectly, the construction industry with its demands for energy-intensive concrete, steel and aluminium plays a significant role. Other factors include modern soil-disturbing farming practices; forest destruction and land-clearing; and methane released by landfills, farm animals and rice paddies.

As awareness of this global problem grew during the 1990s, the world came together to negotiate the Kyoto Protocol, an emissions-reduction agreement that came into force two years ago. At the time of writing, Kyoto had been ratified by 166 countries, and under the first round of targets, developed nations have agreed to a collective emissions cut of 5.2 per cent by 2012.