A Bill we can't pay

4th May 2007
By Alice Bows and Kevin Anderson

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Within its climate change programme of 2006, the government reaffirmed its support for avoiding dangerous climate change and limiting global temperature increases to not more than 2°C above pre-industrial levels.

Now, in a bid to transform rhetoric into reality, it has published a draft Climate Change Bill enshrining its long-standing 60% carbon dioxide target. Amongst the new measures and powers to more easily facilitate a transition to a low-carbon economy, the Bill proposes that the 60% reduction by 2050, with reductions of 26% to 32% by 2020, becomes legally binding.

At the time the target was first being considered, the 60% was linked to the 2°C temperature rise. Unfortunately, in light of an improved scientific understanding suggesting that much more substantial emission cuts are likely to be required, the 60% target is now more closely related to a 4°C rise than the original 2°C level.

To shed light on this discrepancy, the link between global temperatures and national carbon targets requires consideration. For nations to translate a global problem to the national scale, making the leap from a global temperature threshold to a national carbon reduction target is not only helpful but arguably essential. To explore how the government arrived at its 60% target we must therefore follow the trail back from temperature change to global carbon dioxide concentration through to global and subsequently national cumulative carbon budgets (the ‘correlation trail’).

Following the trail provides us with the equivalent to a global carbon bank account with a limited budget to spend over a given period. By apportioning our global carbon budget to individual nations (the apportionment regime) we arrive at an associated national budget for that period.

As a first step along the trail, a future global temperature can be linked to a range of future atmospheric carbon dioxide concentration levels. For example, if atmospheric carbon dioxide were to stabilise at 450ppmv (not including the other greenhouse gases), there is approximately a 70% chance of exceeding the 2°C threshold.

In the next step, by using global climate models, the chosen carbon dioxide concentration can be linked to a global cumulative emission budget over a fixed period of time. The scientific community has a considerable degree of understanding of how much carbon dioxide can be released globally over the coming century to achieve a chosen level of carbon dioxide concentration. However, uncertainty in the science dictates that a range, rather than one value for cumulative emissions, emerges.

The final step along the trail inevitably incorporates both political decisions relating to global emission apportionment regimes, and scientific uncertainties. Nevertheless, disagreements over which apportionment regime to use, or the size of the uncertainties involved, pale into insignificance when the scale of the challenge industrialised nations face is met head on.

UK citizens currently emit more than three times the amount of carbon dioxide per person than Chinese citizens. There is no getting away from the fact that nations like the UK have a difficult road ahead if temperatures are to remain below the 2°C threshold.

The method linking global temperature changes to national carbon budgets (as outlined earlier) is clear enough, so how has the government so significantly underestimated the challenge faced and set the UK down a 4°C rather than 2°C path? Three crucial aspects appear to have been overlooked.

First, the scientific understanding from which the 60% target emerged has moved on. To have more of a chance of limiting the rise in temperatures to no more than 2°C, aiming towards a carbon dioxide concentration of 450ppmv is more appropriate than 550ppmv. Clearly, by aiming for a lower carbon dioxide concentration, there will be a smaller global carbon budget to spend.

Second, the government’s target omits the UK’s two fastest growing sectors in terms of carbon emissions — international aviation and shipping. The atmosphere is blissfully unaware of the sectors governments have chosen to include or exclude. The danger here is that if other nations follow the UK’s leadership, aviation and shipping will remain outside of global and national efforts to curb emissions in the short-term.

The third aspect relates to a misunderstanding of the challenge of significantly curbing emissions in the short-term, and the consequence this has on tomorrow’s year-on-year emission reductions. It makes sense that if you spend a quarter of your monthly salary in the first few days, you won’t be leaving yourself much for the last two weeks or so. The analogy to carbon dioxide emissions is illustrated in the graph above.

The solid line presents the carbon dioxide emissions released or ‘spent’ by the UK in the first six years of this century, when aviation and shipping are included. It is then assumed that under the current policy regime all sectors of the economy, excluding international aviation and shipping, stabilise emissions at current levels.

The reality is that in some years the emissions from households, industry and domestic transport may reduce, but in others they may increase. For example, last year there was a shift from gas to coal for electricity due to energy prices; this led to higher emissions from electricity during 2006, despite policies being in place to curb emissions.

Emissions from international aviation and shipping are not assumed to stabilise, as there are no policies currently active to bring this about. Instead, they continue to grow at slightly lower rates than presently until 2012.

If the UK takes this somewhat more realistic short-term carbon pathway, it will have spent a very large portion of its carbon budget early on, and so, to remain ‘in the black’, emissions must subsequently decline at unprecedented rates until the 2030s. In this way, the UK can play a fair part in the global effort to keep temperatures below the 2°C threshold.

If, however, we look at the government’s reasoning, it is clear where it has gone wrong (see the dashed line on the graph). First, because of the difference between aiming for 550ppmv instead of 450ppmv, it believes it has a bigger carbon budget to spend (by some 20% or so).

Second, the omission of international aviation and shipping emissions further makes its spending artificially low and results in higher carbon dioxide concentrations and associated global temperatures than it claims to be aiming for.

Third, it is assuming that emissions are beginning to decline from the outset, but such a decline is not evident from current data. Even using the government’s misguided reasoning, the carbon bank balance is falling quickly, with some 17% of the 50 year budget spent in the first six years of this century. However, this compares with a huge 25% of the budget being blown in six years if its misguided assumptions are corrected.

The Tyndall Centre’s 450ppmv emission pathway demonstrates that in order to achieve a 30% chance of not exceeding the 2°C threshold, the UK must slash emissions by around 90% by 2050. So what temperature does the government’s 60% target relate to if the missing aviation and shipping emissions, and likely continuation of emission increases, are taken into account? The answer must retrace the steps from national carbon budgets back up to global temperature responses.

First, the adjusted 60% target results in a significant overspend of the UK’s national carbon budget between 2000 and 2050. Second, and based on the idea that international aviation and shipping must be taken into account globally, the global carbon spending also goes into the red. Higher global carbon spending (or budgets) means higher atmospheric carbon dioxide concentrations, and in turn, higher temperature increases. Comparing the newly calculated global carbon budget with concentration levels suggests that the government’s target is more in tune with a concentration of 600 to 750ppmv. These concentrations relate to future temperature increases with an estimated 50% chance of exceeding the 4°C level.

This journey down the ‘correlation trail’, in providing an explicit and sequential process, illustrates how spending the budget too early results in much more stringent action being required in the future. Furthermore, it provides an opportunity for informed adjustment to the carbon pathway in accordance with the evolving science of climate change.

Yet even in its current draft form, the Bill states that the 60% target is a unilateral target ‘which we would only change in the event of significant developments in scientific knowledge about climate change’. Clearly the government needs to take heed of the evidence already available. Neither should it continue to hide behind Kyoto’s omission of the international aviation and maritime sectors as an excuse to ignore these emissions.

And if, as the case may be, the government is fully aware that these targets will be contributing to a world in which temperatures are set to rise much more substantially, it would be helpful to inform those armed with the task of adapting the UK to climate change sooner rather than later.

Dr Alice Bows, is Senior Research Fellow, and Dr. Kevin Anderson, Director of the Energy and Climate Programme, at the Tyndall Centre Manchester. The Tyndall Centre’s briefing note can be found at http://tyndall.webapp1.uea.ac.uk/publications/briefing_notes/bn17.pdf

Filed Under: Climate Change, Carbon Emissions
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