Building our own asteroid

• Peter Christoff
• The Age, July 2, 2008

ILLUSTRATION: JUDY GREEN

The Earth is headed for destruction unless we make deep cuts to emissions.

LIFE on Earth has had its ups and downs. Over the past 4 billion years, it has barely survived five mass extinction events, each most probably triggered by a collision with an asteroid or comet. Some 250 million years ago, nearly 90% of all sea species and 70% of all vertebrate land species suddenly became extinct. About 200 million years ago, another collision wiped out roughly half of all species, and ushered in the age of dinosaurs. Then 65 million years ago, an asteroid wiped out the dinosaurs and made room for the age of mammals — including, eventually, humans.

For the past 200 years, we have been blindly building our own asteroid — it is called climate change. Since 1990, despite increasing knowledge of the consequences, we have been adding to its size at a frenzied pace.

Climate scientists believe that global warming of two degrees above pre-industrial levels significantly increases the chance of "dangerous" climate change, during which abrupt and dramatic shifts in climate may occur, with catastrophic social, ecological and economic consequences.

Recent climate modelling suggests that, if atmospheric concentrations of greenhouse gases stabilise at 450 parts per million carbon dioxide equivalent, we will have between a 25% and 80% chance of global average warming exceeding two degrees above pre-industrial levels. Here's the first bit of bad news. We are almost there now.

Now the second bit of bad news. Without substantial and rapid cuts to global emissions, we will not only "overshoot"' 450 ppm carbon dioxide equivalent but remain well above this level for a long time. And here's the third bit of bad news. The risks and levels of extinction increase as global greenhouse gas levels — and temperatures — rise. Planet-wide, some 20% to 30% of land-based plant and animal species are likely to be at high risk of extinction by 2100 as global mean temperatures exceed a warming of two degrees to three degrees, and up to 50% of species once temperatures rise well beyond three degrees.

But even two degrees will be too high for certain Australian ecosystems. Warming of between 1.5 to two degrees will lead to significant losses of endemic species in Queensland's wet tropics; frequent bleaching episodes and loss of much of the Great Barrier Reef; and a further drop of between 13% and 27% of flow in the Murray Darling even by 2030. The higher we go, the worse it gets.

In other words, the notion of "safe" or "dangerous" climate change really depends on where you are, who you are, or what you are. "Dangerous" climate change for much of Australia starts well before two degrees.

This understanding must condition our thinking about the emissions targets that Australia champions, locally and in international negotiations. We improve our chances of keeping global mean temperature below two degrees only by ensuring atmospheric greenhouse gas concentrations rapidly return to below 400 ppm carbon dioxide equivalent. That requires developed countries to cut their emissions by more than 40% by 2020.

Since 1996, the Australian debate about climate change has been framed in narrow economic terms, by what John Howard defined as "the national interest": what is the least we have to do to change our lifestyles and disrupt the economy to protect our existing individual or corporate interests?

Yet the emissions targets we choose should depend on answering two different and prior questions. First, what will we accept as "safe" for our continent and our planet — what do we want to pass on to our children and future generations? And second, what are the likely risks and ecological and social consequences of adopting particular targets?

At present, chasms exist between what scientists are telling us about the chances of dangerous climate change, what our politicians support as viable targets, and what most people understand these targets will deliver. We have not had a full and public discussion about the purpose of emissions targets — about what our collective goals should be, and what we are prepared to keep or lose.

During the last election, Labor campaigned hard on climate change. Kevin Rudd's welcome first act in government was to ratify the Kyoto Protocol. Labor also supports all developed countries committing to emissions cuts of between 25% and 40% below 1990 levels by 2020. And it has enshrined a national emissions reduction target of 60% below 2000 levels by 2050.

Unfortunately, these targets are inadequate when assessed against the available science. Labor's climate policy leads to the destruction of many of our continent's iconic ecosystems and species and reinforces the likelihood that we will precipitate dangerous climate change.

We insure our houses against a slight chance of theft or fire. Planes and nuclear reactors are designed to a very high level of mechanical safety because of concerns about the risk and consequences of catastrophic failure. Most industrialised countries — including Australia — fund substantial health and defence expenditure on the basis of deterrence and risk minimisation. Why accept a much higher risk of failure for our continent and our planet?

This is the debate we should have once the Garnaut inquiry's draft report is released later this week. The targets that Australia adopts nationally, and champions internationally, must reflect what we as Australians choose as the risk of unacceptable — or "dangerous" — climate change.

If we decide that we want to avoid a high risk of species extinction, and the degradation or loss of critical economic and social systems, we will have to choose short and long-term goals that meet these purposes.

Only international agreement among developed countries to ensure deep, rapid and early cuts to greenhouse emissions — beginning with a reduction of more than 40% by 2020, the target Germany adopted last year — will begin to deflect our own asteroid.

Dr Peter Christoff teaches climate policy at the University of Melbourne and is vice-president of the Australian Conservation Foundation.

http://www.theage.com.au/opinion/building-our-own-asteroid-20080701-2zze.html?page=-1