There’s been a lot of attention paid to the environmental evils of plastic shopping bags of late.

Old-style, single-use, non-recycled plastic bags are consuming fossil fuels, choking up the landfills, polluting the waters, and killing bird and sea life. They’re environmental nasties.

There’s plenty of community awareness about this, and several high-profile campaigns have been effective. The pressure has been building to the point where several Australian governments are now considering a ban or a tax on plastic bags at checkouts.

Let’s look at a crucial aspect: greenhouse gas emissions. According to a 2002 official study (PDF, p.76), a typical Australian household might be responsible for 6 kg of (CO2-equivalent) greenhouse gases annually as a result of using old-style plastic shopping bags. And, by switching to re-usable bags, this could drop to 0.6 kg.

Sounds like a big plus.

But… it’s not. It’s utterly trivial.

Compare, for instance, to the gain when a typical household switches to green power: 8 tonnes less greenhouse gases per year. And, in places like Canberra, where people feel the need to warm their houses more than some other parts of the country, it’s higher: I just calculated that our 100% green power saves something like 12 tonnes a year.

And pause, for a moment, to reflect that each litre of petrol we use generates about 2.5 kg of greenhouse gases.

So an entire year of good intentions in avoiding plastic shopping bags is worth… two litres of petrol. Or green power for one evening.

Our household saves around two thousand times as much greenhouse gas simply by using green power.

Now, greenhouse is not the only issue with plastic bags, to be sure. But it’s a pretty big part of it. The campaigns are well intentioned, and the solutions are a nice example of the reduce-reuse-recycle principle. But… the amount of time, energy, and most of all, media and political attention spent on the issue has been way out of proportion to its environmental significance. I mean, have we seen two thousand times more attention given to household green power than plastic bags? No. Amazingly, the issues have had roughly equal coverage.

The harder problems get pushed to the background – the ones that do involve a lot of environmental damage, the ones that certain head-in-the-sand governments and their scriptwriters don’t want to tackle.

Plastic bags are the perfect way for backward-looking governments with vested interests in the fossil fuel business to appear to be doing something green. Plastic bags are highly visible – in every kitchen, a daily reminder of consumption, made of plastic – and taxing them is an easy (indeed, profitable) way for governments to acquire some much-needed mainstream green credibility.

But it’s like watering the houseplants in the face of the firestorm.