Posted on 25 October 2010 by John Cook

The Irregular Climate podcast has just released Episode 13. This week features the most important news in the history of the universe, the simple reason why we should deal with environmental degradation, how CO2 controls the planet’s temperature, a denier distraction, Michael Mann fights anti-science and the University of Virginia fights the Cuccinelli witch hunt. For the Skeptic Debunk of the Week, I revisit a theme touched upon in the recent blog post on the hockey stick:

Skeptic Debunk of the week: Climate's Changed Before

A popular skeptic argument is that ‘climate has changed naturally in the past and therefore recent global warming must be natural’. Of course, this argument is logically flawed. It’s akin to saying ‘forest fires have happened naturally in the past so any forest fires that happen today must also be natural’. But curiously enough, we don’t see a swelling movement of ‘arson deniers’ flourishing on the internet.

Picking logical flaws in this argument is one thing but where it gets really interesting is when you look at the science of past climate change. Believe it or not, scientists are aware that climate has changed in the past. In fact, the past gives us vital clues about how our planet responds to the various drivers of climate. We can see what happens when the Earth builds up heat, whether it be due to more sunlight or rising greenhouse gases. When heat builds up, of course it gets warmer. But the crucial discovery from examining different periods throughout Earth’s history is that positive feedbacks amplify the initial warming.

This is why we see dramatic climate change in the past. Positive feedbacks take any temperature change caused by the sun or volcanoes or greenhouse gases, and amplify them. Positive feedbacks are why our climate is so sensitive to greenhouse gases.

So can you see the irony? Skeptics talk about past climate change as if it disproves the human influence on global warming. But the peer-reviewed science that examines past climate change actually comes to the opposite conclusion. Past climate change provides evidence for positive feedback that amplifies the warming caused by our CO2 emissions.

UPDATE 26 Oct 2010: A new climate podcast has just been launched called The Climate Show. The fact that the title "The Climate Show" is available demonstrates just how few climate podcasts there are kicking around these days and this is a welcome addition. It's a web-based “radio with pictures” programme about climate news science, policy, politics and solutions. It’s the brainchild of KIWI FM’s Radio Wammo breakfast host Glenn Williams and Gareth Renowden from Hot Topic. The back-and-forth between the two has me reminiscing to those days when Dan Moutal and Graham Wayne were bantering away on Irregular Climate, before Dan exploded Graham 10:10 style (or so the rumour goes :-).