Wrong figures, so the wrong target

1st December 2007
By Roderick Crawford

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The aim of the government’s and the EU’s climate change strategy, as stated in Climate Change: the UK Programme 2006 (and in the 2003 energy white paper) is ‘limiting average global temperature increases to no more than 2˚C above pre-industrial levels’.

A future global temperature can be correlated with a range of future atmospheric carbon dioxide concentrations. To limit climate change to 2˚C, global atmospheric carbon dioxide concentrations need to be stabilised at or below 450 parts per million.

To achieve this requires not simply reducing current CO2 emissions to a new level — 60 per cent reductions on 2000 emission levels, according to the government — but rather limiting the total amount of CO2 and other greenhouse gases emitted during the target period (2000-2050); it is this volume, not the annual output in 2050, that will determine global average temperature changes. This is equally true of future target periods too.

Understood in this light, the key measure is not an emission target for 2020 and 2050, but a total global budget of CO2 which can be emitted during the period. From this it is possible to establish national emissions budgets by using an ‘apportionment regime’.

Once a national budget is established, an ‘emissions’ pathway’ can be generated; initially following actual emissions data (eg 2000-2006) this pathway can describe alternative future pathways, all of which must not exceed the cumulative emission budget.

The approximate pathway that is described by the Climate Change Bill (see figure) equates to a UK cumulative carbon budget of between 5.5bn and 6bn tonnes of carbon dioxide 2000-2050. This excludes international aviation and maritime emissions on the basis that they are not covered by the Kyoto Treaty’s targets; however, they cannot be ‘removed’ — in the real world they are emissions and contribute to global warming. Added back in, total UK emissions for 2000-2050 rise to between 7bn to 7.5bn tonnes of CO2.

This is way above the available CO2 the UK has to emit during this period for temperature levels to rise by no more than 2˚C. According to the Tyndale Centre, to maintain atmospheric concentrations of CO2 at no more than 450ppm the UK’s must emit no more than 4.5bn to 5bn tonnes of CO2.

Their estimate of UK emissions of 7bn-7.5bn tonnes puts the UK 40-60 per cent higher than is permitted if concentrations are to be stabilise at 450ppm — the stated aim of both the UK and the EU — and would result in global concentrations of between 600ppm and 750ppm. Based on widely used correlations between atmospheric concentrations of CO2 and temperature, the Climate Change Bill supports a 50 per cent chance of exceeding a global temperature change of 4˚C above pre-industrial global temperature levels.

What organisations like the Tyndale Centre are saying is that the science doesn’t support the targets set out in the Bill. Not just because the percentage reductions are too low, but because the target misunderstands what is being measured. It is volume of emitted CO2 over the target period that is key, not where we happen to be in annual emissions figures in 2020 and 2050 — the interim and final target dates.

The misunderstanding of the science of climate change that the Bill suggests is staggering. It would fail at ‘A’ level, never mind degree. How much more embarrassing at the parliamentary level.

It can still be amended so that the targets in the Bill can help the UK play its part in tackling climate change successfully. First, though, the government must decide whether it is still committed to limiting temperature change to 2˚C or to prepare for the adaptation necessary for a global temperature change of plus 4˚C.

Roderick Crawford is editor of Parliamentary Brief.

Filed Under: Climate Change, Climate Change Bill, Queen's Speech
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