Let's talk about rising temperatures, sinking islands and pack ice ...

Well, it turns out that none of the above is unambiguously true.

About rising temperatures: even though industrialisation began to add CO2 to the atmosphere in the early 19th century, the earth cooled down between 1940 and 1976, warmed from 1976 to 1998, and has been cooling down since 1998. I'll let the experts quibble over the details. What is clear about the record is that the record is not clear.

Sinking islands. One factor I never thought of is that the surface of the earth rises and falls. More than 150 years ago Charles Darwin showed that coral atolls grow on top of sinking volcanoes. As for Tuvalu, the Pacific island nation which is in danger of sinking under the waves, the land beneath it is sinking and the local ecology has been trashed when US Marines quarried the coral for a World War II airstrip. Its problems are real, but not necessarily due to global warming.

Temperatures in the Arctic rise and fall mysteriously. The Arctic was considerably warmer between 1920 and 1940. Temperatures have risen in recent years, but on August 11, 2008, the area of the ice pack was 30 per cent greater than a year before.

And industrial activity is a very, very, very minor factor in generating CO2. Plimer points out that the atmosphere only contains 0.001 per cent of the total carbon in the top few kilometres of the planet. Furthermore, I was fascinated to learn that earthquakes and volcanoes are a major source of CO2. About 85 per cent of the world's volcanoes are under the sea. Their CO2 emissions and warming effects were not included in the IPCC reports, he says.

But can't anthropogenic CO2 push us past the "tipping point"? "Tipping points are a non-scientific myth," snorts Plimer. And indeed, the first I ever heard of tipping points was in a best-seller by Malcolm Gladwell. If climate science is scavenging in the rubbish bins of pop sociology for explanations, you really do have to ask some questions.

Plimer makes two simple and challenging points. First, climate is always changing. In the past, the earth has been both much colder and much warmer than it is today. It is exceedingly difficult to understand, let alone what causes these changes. Second, the sun is the single greatest cause of fluctuations in the heat of the earth. Very small changes in solar output have a profound effect upon temperatures. The sun is the single greatest agent in climate change, not CO2, he maintains.

As he wrote in a recent article in The Australian:

In the past, climate change has never been driven by CO2. Why should it be now driven by CO2 when the atmospheric CO2 content is low? The main greenhouse gas has always been water vapour. Once there is natural global warming, then CO2 in the atmosphere increases. CO2 is plant food, it is not a pollutant and it is misleading non-scientific spin to talk of carbon pollution. If we had carbon pollution, the skies would be black with fine particles of carbon. We couldn't see or breathe.

What about criticism from colleagues? Plimer isn't worried. "You can count the number of scientists who are critical of me on a sawmiller's hand," he told me, and nearly all geologists will agree with him. I sensed a certain professional scorn for anaemic nerds who massage computer models of climate under fluorescent lights instead of getting sweaty and sunburned fossicking for strange rocks.

"The reason I put this book out," he says, "is to start a debate. The fact that I've now flushed out a few scientists to criticise me in public is wonderful because we've never had a [scientific] debate. Consensus is a word of politics; it's not a word of science."

Plimer, a man who has spent much of his life in outback mining towns, complains that many of his colleagues are smug elitists. "The reason this book has been a publishing sensation is that a lot of scientists in the media have treated their reading audience with absolute disdain," he says. "They've spoken down to them; they've been arrogant. The average punter might not have the education that you and I have, but he is not stupid. He knows there's a smell, even if he can't tell where the smell is coming from."

Without a lot more study, I don’t feel competent to judge whether Al Gore or Ian Plimer is correct about the urgency of global warming. Elitists may be insufferable, but often they’re right.

But contrarians are not always wrong. Remember Barry Marshall, another rough-hewn Aussie? Just a pain-in-the-proverbial guy with a crackpot theory - some nonsense about bacteria causing stomach ulcers, not spices and stress. His colleagues thought he was a quack. Drug companies sneered. You know what? He was right. In 2005 he won the Nobel Prize in medicine.