Calculating Britain's Carbon Debt

The Climate Change Act of 2008 commits the UK to an 80% reduction of emissions relative to the 1990 level, by 2050.

This was a significant achievement for both the environmental pressure groups and the government of the day, and set a vigorous standard for other countries to follow.

But is it enough to meet Britain’s responsibilities in sharing the burdens of preventing ‘dangerous climate change’, which the UK signed up to at Rio in 1992?

  Summary diagram of the various 'frames' that can be applied to emissions associated with the UK, explained  here.  Click on the image to enlarge it

Summary diagram of the various 'frames' that can be applied to emissions associated with the UK, explained here. Click on the image to enlarge it

The key quantity is the concentration of greenhouse gases in the atmosphere. Because GHGs tend to persist for a long time, it does not help much to announce emissions for a single year, whether it was better or worse than the year before, or the level you intend to reach in thirty years. You need to add everything up and track cumulative emissions – the total between your start date (in this case 2008) and an internationally-agreed end date, usually 2050.

On this metric, how does the UK plan look? Of course it depends somewhat how you cut the cake, but ‘preventing dangerous climate change’ limits global emissions between 2008 and 2050 to about 1000 billion tonnes. The UK’s ‘fair share’ of this is surely proportional to its population relative to that of the world as a whole, and it comes out at about 200 million tonnes a year, or 8400 million over the whole period.

Now go back to the UK plan to 2050, and add everything up to 2050 – which the government has noticeably failed to do. The total comes to about 16600 million tonnes – about twice as much as its fair share.

This is a dark secret at the heart of UK climate policy, and it is no wonder DECC refrains from publishing the simple calculations.

On the face of it then, by 2050, the UK will have accumulated a ‘carbon debt’ of about 8 billion tonnes. Bad enough, but this is to take a very parochial view. The calculations only include emissions from the territory of the UK; they ignore international shipping and aviation and the emissions required to supply all the UK’s imports. Surely we should include these in the tally of emissions for which the UK is responsible? If so, these double the carbon debt to around 16 billion tonnes.

But what about the emissions that took place before 2008? They are nearly all still there in the atmosphere, reducing the available ‘carbon space’ for everyone else. Any international negotiation is bound to take at least some of these ‘historic emissions’ into account. But how far back should we go?  A widely agreed date is 1992, because in that year the UK committed itself to action.  

So now add all the emissions back to 1992, and the carbon debt climbs to about 34 billion tonnes.  Well, DECC?