Scientist Tim Flannery has proposed a radical solution to climate change which may change the colour of the sky.
But he says it may be necessary, as the "last barrier to climate collapse."
Professor Flannery says climate change is happening so quickly that mankind may need to pump sulphur into the atmosphere to survive.
Australia's best-known expert on global warming has updated his climate forecast for the world - and it's much worse than he thought just three years ago.
He has called for a radical suite of emergency measures to be put in place.
The gas sulphur could be inserted into the earth's stratosphere to keep out the sun's rays and slow global warming, a process called global dimming.
"It would change the colour of the sky," Prof Flannery told AAP.
"It's the last resort that we have, it's the last barrier to a climate collapse."
"We need to be ready to start doing it in perhaps five years time if we fail to achieve what we're trying to achieve."
Prof Flannery, the 2007 Australian of the Year, said the sulphur could be dispersed above the earth's surface by adding it to jet fuel.
He conceded there were risks to global dimming via sulphur.
"The consequences of doing that are unknown."
Professor Flannery, who spoke at a business and sustainability conference in Parliament House today, said new science showed the world was much more susceptible to greenhouse gas emissions that had been thought eight years ago.
Regardless of what happened to emissions in the future, there was already far too much greenhouse gas in the atmosphere, he said.
Cutting emissions was not enough. Mankind now had to take greenhouse gases out of the air.
"The current burden of greenhouse gas in the atmosphere is in fact more than sufficient to cause catastrophic climate change," Prof Flannery said.
"Everything's going in the wrong direction at the moment, timelines are getting shorter, the amount of pollution in the atmosphere is growing."
"It's extremely urgent."
As well as the global dimming plan, Prof Flannery said carbon should be taken out of the air and converted into charcoal, then ploughed into farmers' fields.
Wealthy people should pay poor farmers in tropical zones to plant forests - possibly through a direct purchase scheme like the eBay website.
And all conventional coal-fired power stations - which did not have "clean coal" technology - should be closed by 2030.
Capturing carbon emissions from coal-fired power stations and storing it underground - called carbon capture and storage (CCS) - was a good idea, Professor Flannery said.
He urged Australia to dramatically fast-track CCS research and give the technology to the Chinese, who are building the equivalent of one new coal-fired power station a week.
Prof Flannery said while the Rudd government was doing more to tackle climate change than its predecessor, it was still "nowhere near enough."
He called on the government to remove the means test on the $8,000 rebate for domestic solar panels introduced in last week's budget.
"It's probably the bureaucrats getting in the way, we all know that sort of policy is not going to work," he said.
