Author: Andrew Nind

I have been asked to write a piece about carbon offsetting: in particular, its merits and demerits. So here goes.

Carbon offsetting is the practice of paying someone else to take action to reduce carbon emissions somewhere else in order to compensate for one’s own carbon-emitting activities. Offsetting may be done individually or collectively. I cannot do better than Google or Wikipedia when it comes to listing the ways it is done or the companies that will take your money. But what are the pros and cons?

Let’s begin with the pros.

The merits of offsetting

Greenhouse gas emissions are a global problem: what matters is the overall level in the atmosphere, not where they were produced. As such, it makes sense to tackle the problem by searching internationally for the cheapest and easiest abatement measures. If carbon emissions can be reduced in Brazil, say, for a small fraction of the cost of reducing them in Britain, then humanity should collectively take the Brazilian action first. (It does not have to be either/or of course.) It need not be Brazil that pays: in fact it seems fairer for citizens or shareholders in richer (and more polluting) countries to foot the bill. This, in principle, is what carbon offsetting achieves: cost-efficient emissions reduction funded by polluters around the world.

This is akin to the idea of comparative advantage in economics: if a particular nation is able to produce a good more easily and cheaply than other nations, due to having better natural resources, human resources, access to capital and/or infrastructure in place, then – assuming production of the good is beneficial overall – it makes sense for that nation to produce at least as much of it as other countries.

Offsetting measures are usually advantageous in themselves. Cleaner forms of electricity production, methane capture, water purification, efficient cooking stoves, tree planting: if carefully managed to ensure that individuals are not unfairly treated (e.g. landowners losing their land to a new electricity generation project), such projects are likely to increase net welfare.

After a while, the offsetting measure may be ‘used up’ or become more expensive and no longer be efficient from this global cost perspective. That’s fine – there is no reason why the choice of offsetting measures cannot be altered in future.

The problems with offsetting

But there are difficulties, the first of which is verification – verification both that the money is getting to the project and that the project is effective. Can it be demonstrated that the funds are not being siphoned off by corrupt officials? Can it be verified that the same project has not already been sold to others, due either to corruption or mismanagement? Can it be demonstrated that the offsetting scheme is successful in reducing carbon emissions? At the cost expected?

A more complex issue is called additionality. Can it be demonstrated that the offsetting measure is ‘additional’ in the sense that it would not have happened anyway in due course? If, say, a new hydro energy scheme is probably going to be developed whether or not it receives extra support in the form of carbon offsetting revenues, then these revenues increase the profit of the developer but fail to support an overall reduction in emissions. Additionality is hard to establish because it needs people to agree on what would have happened without offsetting.

Then there is an interesting debate to be had on the topic of moral hazard. If people feel protected or absolved from the consequences of actions that are risky or harmful, they may be more likely to engage in those actions. George Monbiot has compared carbon offsetting to the 16th century Catholic Church practice of selling indulgences. By giving money to the Church, people could buy pardons for perceived wrongdoing and without repentence shorten a nasty stint in purgatory. Analogously, paying for offsetting expiates the sins of a polluting lifestyle, allowing the purchaser to avoid the inconvenience of altering it.

From a practical viewpoint, the validity of this argument depends on whether the difference between the carbon footprints of the guilt-free offsetter and the remorseful non-offsetter exceeds the savings from the offsetting measure itself. If the lifestyle of the would-be offsetter is the same whether or not they make payment, then this argument is more of a moral one than a practical one. In an effort to make sure this is the case, some offsetting companies (in contradiction to the pure theory of comparative advantage) actively encourage participants to reduce their own emissions first, where they can, before they buy carbon offsets.

There is, however, a risk that in setting a monetary price for offsetting, companies establish a benchmark in people’s minds as to the value of climate change. To date, the price of offsetting has been relatively low – e.g. £7/tCO2, a price at which the additional cost of say a trans-Atlantic flight is relatively insignificant. Low prices create the false impression that we don’t need to spend much, and hence don’t need to change much, for serious climate change to be averted.

It is frustratingly difficult to know exactly what a carbon offsetting company does with the money one gives it. There is a need for more auditing of these companies. It feels that overall there is a place for carbon offsetting – that it should be ‘net positive’ – but it can never obviate the need for the Western world to change its ways.

Weighing global matter over lunch

Here’s an interesting example of the power of estimation.

Anyone can calculate the Earth’s weight, approximately, sitting in a chair without recourse to a computer, or even paper. It’s a good lunchtime exercise. We just need a few rough facts: the volume of a sphere is about 4 times its radius cubed; the Earth’s diameter is about 8000 miles; a cubic metre of water weighs a tonne.

So – that’s a radius of 4*10^3 miles (half the diameter). Cubing gives 64*10^9 cubic miles. Multiplying by 4 gives 256*10^9. There are 1.6 kilometres in a mile, so about 4 cubic kilometres in a cubic mile. Hence the Earth’s volume is around 1000*10^9, or 1*10^12, cubic kilometres. The Earth’s interior is fairly liquid apparently – all that molten rock – so let’s crudely assume it’s as dense as water. There are 1000 metres in a kilometre, hence 10^9 cubic metres in a cubic kilometre, hence 10^9 tonnes. So overall the weight of the Earth is 10^21 tonnes.

The right answer is roughly 6*10^21 tonnes, according to Google. The main error in the above calculation is that the Earth’s density is nearly six times that of water. But it’s an interesting example of the power of estimation – that most of us are capable via a little mental arithmetic of estimating the Earth’s weight to within one order of magnitude (power of ten).

Estimating the impact of a vegan land release

Emboldened, we could apply the power of estimation to a recent broadcast about the vegan diet.

In New Year Solutions on BBC Radio 4, Jo Fidgen has been exploring everyday solutions to the climate crisis. One of the solutions is to go vegan (or, at least, to cut out most meat and dairy consumption). Apparently about 40% of the land on our planet is now devoted to meat and dairy farming. That’s about 60 million square kilometres. If we go vegan, we could free up much of that land for planting trees – say half of it for the sake of argument, an area equal to the US, Europe and China combined. What does that mean for our carbon emissions?

The best plants in Europe capture carbon at a rate of roughly 15 tonnes of CO2 per hectare per year (Mackay 2009). Given that the best plants might have to be supported by the second-best plants, let’s say vegan-supported tree-planting captures an average of 10 tonnes of CO2 per hectare over 30 million squre kilometres. There are 100 hectares in a square kilometre. So that’s a capture of 100 * 10 * 30 million = 30 billion tonnes of CO2 per annum. The UN projects a population of around 10 billion people by 2050 (Rosling 2018). That’s an extra allowance of 3 tonnes of CO2 per person per annum, freed up by the vegan transformation.

A flying comparison

Let’s put this in context with the example of international aviation. A return flight across an ocean has a carbon footprint – per passenger – of anywhere between 2 tonnes of CO2 equivalent for London to New York and 6 tonnes for London to Sydney. Assuming, that is, economy travel and using Defra’s carbon coefficients, including their figure for radiative forcing (Defra 2018). On average, let’s say a return trans-oceanic flight equates to 3 tonnes per passenger.

Conclusion? If we all became vegan and geo-engineered the world so that we covered an area equal in size to the US, Europe and China combined with carbon-capturing plants – an area that is currently devoted to livestock farming and is hence treeless – then, as a result, we might all be able to have one extra return flight (across an ocean) per annum. By all, I’m including the majority of the world’s population who currently never fly.

There’s also the direct GHG benefit of the change in diet to veganism, which is usually estimated to be circa 1-2 tonnes per person per annum, perhaps more if one gives greater weight to methane emissions (the standard international convention is to calculate the global warming potential of each greenhouse gas, including methane and CO2, over a period of 100 years: if a shorter period is used, then the relative importance of methane compared with CO2, and hence the relative impact of beef-farming versus energy-related activities, is increased).

I don’t know about you, but for me this type of calculation just reinforces the view that either the climate scientists are wrong, or we need to do something major about flying. The 7 billion who don’t fly want to catch up with the 1 billion who do. The physics of flight are not going to change. Battery-powered flying, for long-haul flights, seems unlikely. (The weight of the best batteries is around 100 times that of the equivalent amount of jet kerosene in terms of energy storage. It’s hard to see how a battery-powered plane taking off to cross an ocean would get off the runway.) Biofuels emit CO2. Perhaps future planes will run on hydrogen – but where will the energy come from to produce it?

Flying under the radar

Part of the reason why I go on about flying is that others don’t. Country statistics generally ignore international aviation. It does not feature in the Paris agreement. The EU only tracks emissions in European airspace for its emissions trading scheme. We are told that flying only accounts for a few percent of emissions, when the UK Dept of Transport has published a detailed study (DofT, 2017) showing the figure is at least 10% for the UK – and double that if radiative forcing is taken into account. Other sectors are showing some signs of falling emissions, whilst those from aviation are rising strongly.

Schools encourage foreign trips. Young people love to travel. Business people think face-to-face meetings with partners around the world are essential.

We rich Westerners may have to travel less in the future, not more. When we do travel, perhaps we could train-it rather than plane-it over land. (Cars are no help really: the energy consumption per person is similar for a car and a plane, assuming there are circa 2 people per car.) Crossing bodies of water is hard to do without using lots of energy. Whilst transporting bananas over the sea is surprisingly energy-efficient, most of us don’t want to be stacked like bananas when we travel; and passenger ships to date are no better than planes. Maybe nuclear-powered ships will feature in years to come. Or maybe, if we insist on air travel, we could learn to do so in helium-filled airships and accept the longer time it takes.