Harford on a Carbon Tax

Tim Harford has a good piece on the virtues of a carbon tax:

A friend recently wrote to me agonising over an ethical question. He was pondering a long-haul trip to see his family but was all too aware that the flight would have a huge carbon footprint. Could the journey possibly be justified? I suggested that my friend find out what the carbon footprint was (a tonne of CO2, it turns out) and then imagine a hypothetical carbon tax. Would he still be willing to travel if he had to pay the tax? If not, the trip wasn’t worth it.

My advice raises the question of what this carbon tax should be. At a carbon tax of £5 per tonne of CO2 — plenty of carbon global emissions are taxed at less than that — the extra tax on that one-tonne return flight would be trivial. At a more serious £50, it would be noticeable but perhaps not decisive. (The emissions trading systems in the EU and the UK until recently implied a carbon price of around £50 per tonne of CO2; the UK price has since leapt. US Democrats are pondering their own carbon tax.) If the carbon tax were a deep-green £500 per tonne of CO2, my friend would have to be missing his family more than most of us ever do.

I realise it is quixotic to advise checking one’s personal consumption decisions against a completely hypothetical tax, but it gets to the core of what a carbon tax is for. It isn’t just an incentive to change behaviour; it’s a source of information about which behaviour we most urgently need to change.

Exactly right. Or as Tyler and I say in Modern Principles, a price is a signal wrapped up in an incentive. Put a price on carbon and every actor in the system will be incentivized to follow the signal and reduce carbon use in ways that no one can predict or plan.

Tim concludes:

…A carbon tax changes that by making the climate impact as real a cost as any other. It sends a signal along all those supply chains, nudging every decision towards the lower-carbon alternative. A shopper may decide that a carbon-taxed T-shirt is too costly, but meanwhile the textile factory is looking to save on electricity, while the electricity supplier is switching to solar. Every part of the value chain becomes greener.


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