In 2014, England will follow the example set by Wales and Scotland and introduce a carrier bag charge. If the Welsh and Scottish experiences are anything to go by, the policy will drastically reduce the number of bags in circulation, keeping unnecessary waste out of landfill and removing a little polythene from the diet of our cities' seagulls.

Like recycling, re-using carrier bags has become something of an iconic "sustainable behaviour". But whatever else its benefits may be, it is not, in itself, an especially good way of cutting carbon. Like all simple and painless behavioural changes, its value hangs on whether it acts as a catalyst for other, more impactful, activities or support for political changes.

The evidence from Wales is not encouraging. My colleagues at Cardiff University analysed the impact of the introduction of the carrier bag charge. Although their use reduced dramatically, rates of other low-carbon behaviours among the general public remained unaffected.

To be clear: fewer plastic bags would be a small, good thing. But as a major two-day conference at the Royal Society headquarters in London this week made clear, "every little helps" is a dangerously misleading mantra when it comes to climate change.

The Radical Plan meeting featured contributions from across the physical and social sciences, as well as civil society. The organisers – Professors Kevin Anderson and Corinne Le Quere of the Tyndall Centre – posed contributors a brutally simple question: what would need to happen if we were to do more than simply pay lip service to the idea of avoiding dangerous climate change?

The answers were undeniably radical – and none mentioned re-using plastic bags.

Scientists and engineers described the unprecedented scale of energy system change necessary to decarbonise rapidly. Social scientists argued for a transformation in the way we view ourselves, our consumption, and our role in society. Economists demolished the idea that economic growth could be maintained forever in a fossil-fuel driven, finite world. Policy experts questioned whether our current carbon targets were fit for purpose.

But across almost all of the papers presented at the conference, there was an inescapable consensus: a fundamentally different economic system is required, if we are serious about avoiding dangerous climate change, based on nurturing wellbeing rather than stoking corporate profit.

This is, of course, not a new idea. But what was striking was the convergence across contributors from the breadth of the physical and social sciences. The clear message was that unrestrained capitalism is incompatible with decarbonisation: the sums simply don't add up.

Many sceptics see the issue of climate change as no more than a figleaf for ushering in a new era of socialism. The conclusions of the Radical Plan conference are unlikely to convince them otherwise. But for the vast majority of us – who say we "get" climate change, but still somehow cling on to the idea that small, incremental behavioural changes will be sufficient – the conference should be a wake-up call.

Nudging, tweaking, or cajoling people into piecemeal behavioural changes like re-using plastic bags is not a proportionate response to climate change. Engaging the public through their personal carbon footprints is really only a means to an end – and that end is a political and economic system that has sustainability as its central organising principle.

And if these sound like radical statements, unbecoming of the stately, reserved sentiments associated with the Royal Society, then consider the prospect of a world that is four or even six degrees hotter and the havoc and suffering that would be inevitable. This is also a radical choice.

Clearly, economic systems do not overhaul themselves – and in a democracy, majority support is a prerequisite for any significant societal shift. Politicians do not take risks if they don't think the electorate will support them. And civil society cannot function without a diverse supporter-base.

This means that public engagement still lies at the heart of the challenge of climate change, but it is a form of public engagement that goes way beyond plastic bags. And any public campaign that treats minor behavioural change as a valid goal in itself is also taking a radical stance: complicity in a dangerously warmer world.

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