But buried in Australia's soils are coal reserves that, if dug up, sold and burned as fossil fuel companies plan, represent more than 150 gigatons of C02. "If Australia carries out its expansion plans of new mines that would be roughly equivalent of [releasing] 30 per cent [of the world's carbon budget] between now and two degrees," says McKibben. The world famous climate activist - seen by many as a rock star of the global warming movement (he's been jailed twice for leading protests against the Keystone XL pipeline extension, some of the largest civil disobedience actions in the US for decades) - is in Australia this week for his Do the Maths tour. The campaign, one of several McKibben has founded - including 350.org - was formed off the back of an article the activist penned for Rolling Stone, which went viral last November. The campaign's central message is simple: to save the planet from catastrophic global warming Australia's coal deposits, particularly those proposed in Queensland's Galilee Basin, must stay in the ground.

So must the other 2600 plus gigatons of carbon dioxide in the coal, oil and gas reserves earmarked for extraction by fossil fuel companies around the world. "We have to convince people to get their governments to set policies that keep this stuff in the ground," he said. "If we build new infrastructure now it locks in decades more of doing this stuff." McKibben is encouraging Australians to pressure businesses, organisations and universities to divest in fossil fuel companies. Since the campaign started, a growing number of groups, including the city of Seattle and a dozen US universities and other businesses, have sold their stocks in these corporations.

In April, the Uniting Church of Australia announced it would no longer invest in coal or coal seam gas companies. While Australia's price on carbon was a useful tool to encourage the community and businesses to reduce their carbon foot print, McKibben said the amount of carbon reduced by the scheme would be dwarfed by the amount of carbon extracted from the country's proposed mines. McKibben said as well as being a strong moral position, divestment in the fossil fuel industry was a shrewd economic decision. "All investments are bets, and if you invest in the fossil fuel industry you are betting that the world will never do anything about climate change." "If it does, your investment is a bad one," he said.

McKibben will encourage Australians to lobby their superannuation funds to stop investing in these companies. He said the high level of public support for climate change action tied with the overwhelming scientific consensus had placed fossil fuel companies in a "precarious" position, he said. "It explains part of their rush to build all these mines, ports and infrastructure as fast as they can." But not everyone supports McKibben's economic argument. Two RMIT University economists, Sinclair Davidson and Ashton De Silva, wrote in the Australian in April that "foreigners coming to Australia to campaign against our national economy can do a lot of damage if their claims go unchallenged.

"The consequences of ill-informed meddling in the coal economy would have a massive negative impact in Australia," wrote the pair, who co-authored a recent report on the country's coal industry which was commission by the Australian Coal Association. But McKibben said it was economically stupid for Australia to base its future economy on an industry that was riding a bubble. "And what's economically insane for the world is to deal with the economic effects of rapid climate change," he says. Bill McKibben's Do the Math tour will visit most Australian capital cities this week.