On a hot day, you can smell the Cadbury chocolate factory even before you step inside. Lying on the banks of the Derwent River, just north of Hobart, the factory is a popular destination for sweet-toothed tourists, who come to find out more about the process of combining three ingredients - cocoa, sugar and milk - to make Freddo Frogs and family blocks of chocolate.

But there's one thing that the tour guides don't discuss: the secret in every bite of chocolate. You can't taste it or see it, and it's not listed on the wrapper with the ingredients. It's carbon dioxide.

When we burn fossil fuels for energy, the carbon stored inside the coal, gas or oil binds with oxygen to become carbon dioxide. It's a natural part of the air we breathe. But it's also one of the major greenhouse gases altering our climate because we're now putting more of it into the atmosphere faster than we've ever done before. Until relatively recently, nobody had taken much interest in how much of it is released in the production of everyday products like chocolate.

The electricity used at Cadbury's Claremont factory generates comparatively few greenhouse gas emissions by Australian standards. That's because most of Tasmania's electricity comes from hydroelectricity, produced by running water rather than by burning coal or gas. Where Cadbury's chocolate does rack up a higher carbon count is from the oil burnt for its 'food miles', from transporting the ingredients to their factories through to getting the final products to the supermarket. While the Claremont factory's milk is locally produced in Burnie, their sugar comes from plantations around Mackay in Queensland. Their cocoa comes from even further afield: grown in Ghana in western Africa, roasted and processed in Singapore, before finally being shipped to Tasmania.

All up, the three main ingredients in a block of Cadbury chocolate have travelled more than 21,000 kilometres just to reach Claremont - equivalent to more than five cross-continental trips from Perth to Sydney. And that doesn't even include the carbon dioxide released in other ways, from making the cardboard and plastic for the wrapping to transporting the chocolate around the country.

Of course, the answer is not as simple as everyone boycotting chocolate. The real point is to recognise that almost everything we produce and consume creates greenhouse gas emissions. The challenge we face is to find more ways to reduce those emissions wherever possible, so that we minimise climate impacts while still being able to enjoy the things we value most in life.

Written by Donna Green and Liz Minchin

Extract from Screw Light Bulbs, showing how we can tackle climate change while saving ourselves time and money.