What the Pope's green manifesto should say... 1. Introduce an international carbon tax

To stop the planet overheating will require all kinds of power, so it is a boon that ‘higher’ is joining the fray. Pope Francis is drafting an encyclical – the Vatican’s version of an open letter – on the environment. In person soft-spoken and stirringly humane, in this case The Voice of God will hit a thunderous note. Two weeks ago, Francis gave warning: “God always forgives, we sometimes forgive, but when nature – creation – is mistreated, she never forgives.”

We are at an odd point in climate politics. Today David Cameron drew criticism for promising to slash environmental regulations on the building of new homes. New figures show that government spending on ‘domestic climate change initiatives’ will fall 41 per cent this year, as torrential rains bring river-water into Somerset living rooms. There is consensus that international treaties as they stand will not keep warming within the ‘safe zone’ of 2 degrees Celsius. So how can the Pope help? If rhetoric was enough, the Coalition would be, as Cameron promised, the “greenest government ever”, and temperatures would long have stepped off their dangerous rate of warming.

Here is one suggestion, both practical and presumptuous. Call for an international carbon tax. The Pope has already used the symbolic power of his office to change attitudes - on poverty, on homosexuality, on immigration. Attitudes to a carbon tax might not seem worthy of joining that line-up, but they are, and the Pope is just the person to make the case.

Putting a price on carbon forms the most direct, powerful way of cooling the planet. (Small, low-emitting countries would initially be exempt). As it is clear that poorer parts of the world will be the first to suffer from climate change – in the Philippines, many believe the pain has already begun – a carbon tax would show commitment to not outsourcing the hardship caused, albeit indirectly, by emissions in the rich world. It is not pie in the sky, nor economic insanity. In fact The Economist believes such a tax is needed, and will arrive eventually, when rich countries have exhausted every other option.

How would one look? Compared to the current tangle of ‘green tape’, endearingly simple (though tricky to arrange). If you live in a ‘big’ country, you pay a set tax to burn a tonne of carbon – just like UK citizens pay VAT on every purchase. Governments then redistribute funds raised to the population, ensuring that the tax does not fall regressively. Right now, twenty per cent of global emissions are subject to some form of carbon tax (though in Europe the price is too low to make much difference). If the encyclical is still in draft, Francis should call for the other eighty per cent to join in, and a higher price per tonne. Climate change is one problem – as the Pope no doubt recognises – that prayer alone will not solve.