The Courier-Mail
By: Graham Readfearn
'We may lose some big ice sheets, which can raise sea levels by maybe 20m to 30m'
Tens of thousands of people will converge around one number in countries across the world today to call for action on climate change.
Some of Australia's leading climate change scientists held a discreet briefing for politicians this week and it is almost unthinkable that the number would not have been raised there as well.
But why is the number - 350 - engaging so many people around the world, from the leaders of government to great scientists to everyday Australian folk?
And why is it so crucial?
In short, climate campaigners and many scientists believe that to prevent climate change from presenting civilisation with challenging dangers, the concentration of the greenhouse gas carbon dioxide needs to be stabilised at 350 parts per million in the atmosphere.
"If you keep concentrations of carbon dioxide down to 350, then you've got a higher probability of avoiding some of the major risks of climate change, such as losing big polar ice sheets or putting stress on coral reefs,'' says Professor Will Steffen, executive director of the Climate Change Institute at the Australian National University.
"It is really a matter of how much risk you are willing to take,'' Steffen says.
"As you go up from 350, the risks increase.''
Today's global day of action on climate change, co-ordinated by a long list of campaign groups, including Greenpeace, Oxfam and WWF, has picked 350 as its calling card, but there are some unfortunate realities that endanger their optimism.
Concentrations of carbon dioxide are hovering around the 390 mark. When world leaders meet in Copenhagen in December to agree on a new global deal to limit greenhouse gases, talks will centre around stabilising levels at 450 parts per million. Currently, a 350 target is not so much off the table as on a separate continent.
But Steffen says the 450 target still gives the world only a 50/50 chance of stopping average global temperatures from increasing by 2C, based on pre-industrial levels.
"At 450, coral reefs are really on the borderline. We may lose some big ice sheets, which can raise sea levels by maybe 20m to 30m eventually.''
So where does the magic figure of 350 come from?
The level originates with Dr James Hansen, a leading NASA scientist who has been increasingly outspoken on the need for serious and radical action on climate change.
A paper co-written by Hansen and published in the US-based Open Atmospheric Science Journal last year concluded that allowing levels of carbon dioxide in the atmosphere to remain above 350 parts per million would present "a possibility of seeding irreversible catastrophic effects''.
"Obviously that was a statement with some political connotations,'' says Dr Mike Raupach of CSIRO Marine and Atmospheric Research in Australia.
"All of these numbers are arbitrary but what's important to bear in mind is that these figures originate from a value judgment about what constitutes dangerous climate change.''
The Federal Government has pledged to introduce an emissions trading scheme that will result in emissions being cut by 25 per cent if the Copenhagen meeting agrees on a wide-reaching deal to stabilise levels of carbon dioxide - not at 350 but at the riskier 450 level.
Professor Andy Pitman, co-director of the Climate Change Research Centre at the University of NSW, says politics aside, the ideal target would be 350.
"But you can't put politics aside and so 350 is probably impossible,'' he says. "That's why scientists have been talking about the need for adaptation because we're clearly already experiencing climate change.
"If we could peak at 450 then come down to 350, then we have a 50/50 chance of avoiding dangerous climate change.
"By dangerous, I mean, for example, the loss of the glaciers that provide the fresh water for irrigation to India and China - that's more than 2 billion people. You're certainly looking at the unsustainability of the Great Barrier Reef.
"It's not the end of the world. What we are talking about are substantial changes that impact on our quality of life here - and certainly some people's actual lives.
"We are already seeing deaths from heatwaves due to global warming.''
Peter Grace, Professor of Global Change at Queensland University of Technology, says getting down to 350 parts per million would require one of two things.
"Either a major scaling back of industrial growth worldwide or a major feat of invention in the next five years, both of which are not likely to occur,'' he says.
So, is the 350 campaign an unrealistic waste of time and energy? Grace thinks not.
"On the other hand, 350 parts per million at least poses a target to strive for, as we have a tendency to fall well short of the mark when we have other sound imperatives,'' he says. "Using the same rationale, a 450 target would still place us well in the red zone, hence 350 makes sense, albeit, virtually impossible.''
Join the environment debate on Graham Readfearn's blog at couriermail.com.au/greenblog
For more on the 350 campaign, go to 350.org/australia