Is climate 'the' issue, or is it just one of many?

We sat in chairs dipping down towards the river, facing a Yarra obscured by a geometric lattice-work of steel and glass amid the winter gloom of a late afternoon in Melbourne. The motion to be argued in the recent Deakin Debate at Federation Square was “that climate change is the only issue”.

The stark framing of the motion was clearly chosen to provoke strong argument, even among those members of the audience inclined to endorse quick action on climate change but unwilling to grant the issue primacy among such pressing candidates as armed conflict and global poverty.

An audience pre-poll showed majority resistance to the motion, with the ABC's Peter Mares noting that another poll after the debate would test the persuasiveness of the arguments to be presented.

He introduced the speakers by noting a recent report in The Age quoting Professor Barry Brook's suggestion at a Canberra conference that we are heading towards atmospheric carbon dioxide levels of 600 parts per million (ppm) with up to 6C warming.

Among a range of effects, Professor Brook suggested warming of 3C could threaten the collapse of the Amazon, four degrees the extinction of up to half of the earth's species, and 5C, sea-level rises of 80 metres. If Brook was right and climate change was happening much faster than expected, Mares suggested it might in fact be "the" issue. The debate would decide.

Don Henry, Director of the Australian Conservation Foundation, began the case for the motion with some telling facts. Carbon emissions data retrieved that day from the website of Hawaii's Mauna Loa Observatory showed current levels at 387 parts per million of the earth's atmosphere, compared with 315ppm in 1958 - an increase of 23 per cent in only 50 years.

With many climate scientists now urging stabilisation well below 450ppm to decrease the risk of dangerous climate change, if not guarantee its avoidance, the Mauna Loa data presented by Henry indicate a rise in atmospheric carbon concentrations that, without action, may well exceed stabilisation levels that seem to lower with every new study. Indeed, NASA's James Hansen has already suggested a "target" of 350ppm that we have already exceeded, pressing the case for drastic remedial action on emissions.

For Henry, climate was “the” issue because its “impacts ... are so pervasive across every sector of every society on earth”.

Domestically, he asked who wanted more drought and bush fire, who wanted to lose the Great Barrier Reef and the wet tropical rainforests. Global warming could mean Dengue Fever surviving south of Sydney, Malaria existing "pervasively" in northern Australia, and thousands of older Australians dying of heat stress. Because the effects would be felt globally, the world needed to come together to "tackle the issue, to reach global agreements, to move forward".

Henry presented a two-year window of opportunity for action - domestic decisions based on the Garnaut Review this year, and the negotiation of a new international agreement on climate change in December 2009. This brief window was reinforced in its urgency by climate “feedback loops” that Larissa Brown, the second speaker for the motion, told the audience scientists had already begun to observe.

Brown, who is Founder and Executive Director of the Centre for Sustainability Leadership, noted the diminishing capacity of the world's rapidly melting ice sheets to reflect sunlight that is otherwise absorbed by the earth's surface and radiated as heat.

As Brown explained, when heat is trapped by greenhouse gases accumulating in the atmosphere, yet more ice melts, further reducing reflected sunlight and increasing the radiation of heat and consequent melting. Together, this and other feedback mechanisms threatened to render warming irreversible and beyond our control.