House of Commons - Carbon budgets - Environmental Audit Committee

Carbon budgets - Environmental Audit Committee Contents

2 The global objective

Limiting the rise in average global temperature

6. Average mean global temperature has already gone up by 0.8°C above pre-industrial levels and even if concentrations of greenhouse gases could be fixed at 2005 levels, the world could be committed to an eventual warming of between 1.4 to 4.3°C.[7] In order to say what limit should be placed on emissions we must first decide what constitutes dangerous climate change. Establishing where the boundary between acceptable and dangerous climate change lies is a political question but one that must be informed by science. Defining 'dangerous climate change' is ultimately a value judgement.[8] Lord Turner of Ecchinswell, Chairman of the Committee on Climate Change, explained that this was because of uncertainties in climate science and in our understanding of how human welfare is affected by climate change.[9] Science can tell us what the likely response of the climate will be to a particular concentration of greenhouse gases and what the impacts of climate change will be. But it cannot do this with absolute certainty and what we know is described in terms of probabilities and likelihoods. Political judgement must be exercised to determine where boundaries lie. A report written following a scientific congress in Copenhagen in March 2009 said:

7. Recent observations have shown that societies and ecosystems are vulnerable to even modest levels of climate change, with poorer nations and communities, ecosystem services and biodiversity particularly at risk. A rise in temperature of more than 2°C is likely to cause major societal and environmental impacts through the next century and beyond.[11] In 2001 the consensus was that a rise of 2°C would avoid the most serious impacts. Professor Brian Hoskins, a member of the Committee on Climate Change, said it was quite possible that the world would become a more dangerous place even if the rise in temperature could be kept to 2°C.[12] The synthesis report produced following a recent scientific congress in Copenhagen acknowledged that adaptation strategies would help societies cope with rises of less than 2°C but argued that beyond 2°C the scope for adaptation of society and ecosystems was thought to decline rapidly.[13] We should not be complacent about the kinds of impacts that might occur. It is likely that as temperature rises the cost of adaptation will rise rapidly and those countries that cannot afford to adapt will be most disadvantaged. A key point in the Copenhagen Accord was a commitment to "reduce global emissions so as to hold the increase in global temperature below 2°C".[14]

8. If greenhouse gas emissions continue to rise unchecked, it is likely that global warming will exceed 4°C by the end of the century.[15] The Intergovernmental Panel on Climate Change (IPCC) has said that most developed countries need to reduce their emissions (relative to 1990 levels) by between 25% and 40% by 2020, and by between 80% and 95% by 2050, to have a 50:50 chance of stabilising temperature increases below 2°C. The Government said its targets for reducing emissions and carbon budgets were consistent with the conclusions of the IPCC and its objective was to limit global warming to 2°C.[16] The Secretary of State for Energy and Climate Change, the Rt Hon Edward Miliband MP, told us remaining below 2°C would prove to be very challenging.[17]

9. The Committee on Climate Change decided the UK's objective should be to keep the increase in average mean global temperature by 2100 as close to 2°C as possible and the probability of the increase in global mean temperature exceeding 2-4°C as low as possible.[18] The Committee believed it was no longer possible with certainty, or even with high probability, to avoid the danger zone entirely.[19] There is little chance of keeping temperature increases below 2°C; to do so would require action far in excess of what the Committee on Climate Change had proposed.[20] The goal must be to reduce the risk of exceeding 4°C to the lowest achievable levels. According to the Committee on Climate Change, to meet this objective global emissions must peak soon and then fall at 3-4% per annum thereafter.

10. In setting targets for reducing emissions and carbon budgets the Committee on Climate Change has had to make judgements and compromises.[21] Limiting the rise in temperature to less than 2°C could possibly be justified scientifically[22] (although we are already destined to experience over 1°C of warming based on the current atmospheric concentration of greenhouse gases) and reducing the probability of exceeding 2°C (currently 50%) can be justified against the political and social costs of achieving that goal. However, neither is currently politically feasible, as the outcome of the Copenhagen Summit demonstrated only too depressingly.

11. Professor Paul Ekins, Professor of Energy and Environment Policy at King's College London, accepted that it could be argued that the carbon budgets recommended by the Committee on Climate Change were the maximum consistent with policy possibility and credibility.[23] Lord Turner told us that the Committee had sought to describe a path that was technically feasible, affordable and consistent with limiting the rise in global temperatures to a level that was not catastrophic and that was manageable in terms of the adaptation cost.[24] Professor Hoskins said the Committee had been unable to identify a realistic scenario or credible emissions reduction pathway that went beyond what it had proposed, characterising its recommendations as a compromise between "what is possible, just possible if we really work at it, and what we would like in a perfect world".[25]

12. We accept that the Government is broadly right to use the objective of limiting the rise in average global temperature to no more that 2°C as the backbone for its targets and budgets. But it also needs to be thinking about and planning the options available for reducing emissions further and faster if the scale of the crisis demands bigger sacrifices now to redeem the future. This planning should include strategies for securing political acceptance as well as researching and developing new technical solutions. The Government must be ready, if needed, to establish credible emissions reduction pathways that go well beyond what is currently regarded as politically possible. At the very least this will be needed as an insurance option if doing everything that is currently planned turns out not to be enough. Some policy options, like personal carbon trading, are currently discounted because they are politically unachievable or too costly. The Government must shape and inform public opinion so that the UK will be able, if needed, to reduce its emissions at rates in excess of what is possible currently. A failure to make this investment now could lead to an outcome that is more economically, socially and/or politically challenging than the options that are currently discounted.

PEAKS AND TIPPING POINTS

13. The rate at which we emit greenhouse gases must fall, and fall soon. The Copenhagen Accord recognised the need to achieve "the peaking of global and national emissions as soon as possible".[26] The Committee on Climate Change based its analysis on an assumption that global emissions of greenhouse gases will peak before 2020. While it focused on 2016, David Kennedy, Chief Executive of the Committee on Climate Change, told us that its conclusions do not change much if the global peak in emissions occurs in 2015, 2016 or 2020.[27] But he said the goal of limiting the rise in temperature to 2°C could not be met if global emissions peaked later than 2020.[28]

14. But at present, global emissions continue to rise;[29] a recent report suggested that emissions rose 29% between 2000 and 2008 with all of the growth in emissions in developing countries (although at least a quarter of the growth in these countries was due to the production of goods for consumption in developed countries).[30] The Tyndall Centre has argued that, whilst theoretically a peak in 2016 does permit much lower and more politically acceptable annual emission reduction rates, it is "at best highly optimistic and at worst dangerously misleading".[31] The difficulty and inertia associated with decarbonising energy supply and the growth of emissions from countries like India and China make it unlikely that global emissions will peak in 2015 or 2016.[32]

15. Not all of the carbon dioxide released into the atmosphere remains there. Over half of it is removed by land and ocean carbon dioxide 'sinks'. The fraction of carbon dioxide removed by these sinks has decreased over the last 50 years and there is some evidence that the fraction will decrease further over coming decades under high-emissions scenarios. As this weakening of natural sinks progresses it will become harder and harder to keep the concentration of greenhouse gases in the atmosphere at a level likely to avoid dangerous climate change.[33]

16. Carbon-cycle feedbacks, where a climate induced change accelerates climate change, are not fully understood. The loss of sea ice due to warming seas is an example of such a feedback. It could result in more of the Sun's energy being absorbed by the sea rather than reflected by white ice sheets accelerating the loss of ice sheets.[34] Another feedback mechanism is linked to the melting tundra. Due to global warming permafrost is melting releasing methane that could lead to further warming.[35] The models used in the IPCC process only include fast feedback processes such as changes in sea ice, water vapour and aerosols. Slow feedbacks, such as ice sheet shrinkage, changes in vegetation or changes in emissions from land and sea in response to global warming, could mean that climate change could happen much faster than models predict.[36] The IPCC has acknowledged that its targets for reducing emissions may be underestimated due to missing carbon-cycle feedbacks.[37] They may be missing because they are insufficiently understood for the risks to be effectively quantified.

17. Tipping points occur when a particular parameter in a system changes, causing the system to 'flip' into alternative stable state, for instance, from sea ice to open ocean. Dr James Hansen has argued that they arise where, without any additional change in climate, rapid changes in environmental or ecosystems proceed practically out of control.[38] A study by the Goddard Institute for Space Studies found that global warming of 0.6°C in the past 30 years means only moderate climate change could result in the disintegration of the West Antarctic ice sheet and Arctic sea ice. Dr Hansen has argued that the loss of Artic Sea Ice or the West Antarctic Ice Sheet are potential tipping points.[39] A recent study has reported that the East Antarctic ice sheet, which was thought to be stable, has been losing mass for the last three years.[40] Tim Lenton et al have argued that society may be lulled into a false sense of security by smooth projections of global change as variety of elements within the Earth system could reach tipping points within this century due to man-made climate change.[41] It is difficult to predict when and how a system will flip. It can be a linear response to increasing pressure or occur in a single catastrophic event or a series of catastrophes or as an accelerating and self-feeding disaster. Debate about the resilience of natural systems to such changes is ongoing.

18. Aubrey Meyer, co-founder of the Global Commons Institute, expressed concern about how carbon-cycle feedbacks in climate models and failure of carbon sinks were treated by the Committee on Climate Change in the work that underpinned its recommendations.[42]

19. Irrespective of how quickly the Copenhagen Accord can be translated into a legally binding treaty (if this can happen at all), it is vital that global emissions peak as soon as possible if domestic action on emissions is to be meaningful. Taking action later will cost much more than action taken now.[43] Delay could mean that the rate of emissions reductions needed in the post-peak period would be much more challenging, going beyond what the Committee on Climate Change believes is feasible. It also increases the chance that we will pass some tipping point in the climate system. The Government's position in international climate change negotiations must be predicated on getting emissions to peak as soon as possible. This will be very challenging but a failure to reverse the rise in global emissions before 2020 could render much of the UK's domestic action meaningless. But we have to prepare for the worst, and in doing so drive home the message that a stitch in time is worth nine. The Committee on Climate Change should be charged with and resourced to advise on the changes to the UK's targets for reducing emissions and carbon budgets which may be required if global emissions do not peak by 2020. The impact of global emissions failing to peak before 2020 should be also considered in Defra's Climate Change Risk Assessment so that the implications of failing to set and achieve the necessary budgets can be fully understood. The Committee on Climate Change's Sub-Committee on Adaptation should be asked to consider the implications for adaptive action of global emissions peaking after 2020.

EQUITY AND BURDEN SHARING

20. Rich countries were responsible for emitting around 70% of the current stock of greenhouse gases which dwell in the world's atmosphere. The Kyoto Protocol recognised that there were 'common but differentiated' responsibilities for addressing climate change because of the historic contribution made by developed countries. G8 nations signed up to a global target of 50% reductions by 2050 but recognised that they would need to make much deeper cuts in their own emissions because of the greater responsibility borne by developed countries for the damage already done. Many developing countries argue, with some justification, that their energy consumption must grow and their emissions may have to rise as they grow their economies and lift more of their citizens out of poverty; in India some 450 million people are not connected to the electricity grid.[44]

21. The issues of equity and burden sharing mean different countries face different ethical choices in setting their own targets.[45] Lord Stern, IG Patel Professor of Economics and Government and Chair of the Grantham Institute for Climate Change and the Environment at the London School of Economics, believed that climate stabilisation would need all countries to achieve broadly the same per capita emissions—pointing out the obvious truth that if any large group of people was significantly above average a correspondingly large group would have to be well below average. But the average was sufficiently demanding for it to be unlikely that the latter group could emerge and still retain a feasible lifestyle.[46] The Committee on Climate Change found it difficult to imagine a global deal that allowed developed countries to have emissions per capita in 2050 that were significantly above a sustainable global average.[47]

22. Given a world population predicted to be 9 billion by 2050, per capita emissions will have to be running at about 2 tonnes CO₂e[48] per annum if the concentration of greenhouse gases is not to exceed levels likely to induce dangerous climate change.[49] Each year the United States, Canada, and Australia emit around 20 tonnes CO₂e per capita, Europe and Japan around 10 tonnes, China around 5 tonnes, and India around 2 tonnes, while most of sub-Saharan Africa emits much less than 1 tonne.[50] An 80% reduction would therefore bring Europe down to about 2 tonnes per capita. USA, Australia and Canada need cuts nearer 90%. But even if OECD emissions can be reduced to almost zero, non-OECD countries will have to emit no more than 2-2.5 tonnes per capita as 8 billion people will live there.[51]

23. The Global Commons Institute said that the origins of the advice from the Committee on Climate Change could be traced back to the Royal Commission on Environmental Pollution's advocacy of contraction and convergence in their report 'Energy—the Changing Climate' published in 2000.[52] The Global Commons Institute promotes contraction and convergence as a means of resolving the impasse in international negotiations. Contraction and convergence is a framework for reducing global emissions of greenhouse gases that envisages global emissions peaking and then gradually falling (contraction). It achieves the reduction in emissions by limiting per capita emissions in such a way that they converge (convergence). It entails large cuts in per capita emissions for developed countries while allowing developing countries to continue growing their economies before they have to make cuts to reach equal per capita emissions. Lord Turner said that the advice of the Committee on Climate Change was "reasonably pragmatically close to Contraction and Convergence".[53]

24. The Secretary of State for Energy and Climate Change said it seemed unlikely that contraction and convergence would be the basis of a deal in climate negotiations.[54] He believed it would be opposed in international negotiations; there was no opposition to the basic idea that per capita emissions must converge but probably some disagreement with what that implied about the development paths of particular countries. But he thought it was a useful idea to have in the background of the negotiations.[55] The long-term future must bear some relation to the contraction and convergence model—the only equitable solution in the long-term is equal per capita emissions although the path to such a future will have to take account of the greater burden rich countries must bear.

25. An approach to setting emission reduction targets based on equalising per capita emissions globally is sensible and equitable.

The scientific basis for setting budgets

26. The IPCC's assessment reports represent the best consensus on the science of climate change. But new knowledge is emerging all the time that furthers our understanding of the influence human activity has on climate and the options we have to address it.[56] Lord Turner told us some scientists argued that since the IPCC 4th Assessment Report new information had emerged that made them more concerned.[57] Lord Stern has given four reasons why the position today is more risky than in 2006 when he published his review of the economics of climate change:

· emissions are growing faster than the IPCC trajectory used in the Stern Review;

· the absorptive capacity of the planet, including of the oceans, appears to be lower than many earlier models had assumed;

· new evidence suggests there might be a greater effect on eventual temperature for a given increase in the stocks of greenhouse gases; and

· the physical effects of climate change appear to be happening faster than had been anticipated.[58]

We recognise that it is impractical to re-consider policy each time there is a scientific development. Any policy framework needs some stability if it is to bring about change. Thus questions arise about how often new scientific developments should be reviewed and how they should influence established policy. The challenge is to distil what is robust from what is not.

27. The Association for the Conservation of Energy was concerned that the carbon budgets needed to take account of the latest science[59] and the Met Office recognised that there might be a need to update targets and budgets in light of new scientific evidence.[60] Professor Kevin Anderson, Professor of Energy and Climate Change at the University of Manchester and Director of the Tyndall Energy Programme, saw this as a job for the Committee on Climate Change, which he felt should be "driven by the science with some awareness of the broader political issues".[61] Lord Turner, however, told us that the Committee was not a scientific commission and was not geared up to carry out its own research.[62] While it is vital to take new science and new mitigation options arising from technical and engineering advances into account, none of the recent developments have warranted a change in the Committee on Climate Change's recommendations.[63] The Government "considers that the Committee […] has given full weight to the science in advising on carbon budgets and targets".[64]

28. Lord Turner told us that the Committee on Climate Change accepted the IPCC 4th Assessment Report as the clearest statement of the scientific consensus.[65] It is true that IPCC reports are developed over an extended timescale so that they can be subject to extensive peer review and to allow significant differences to be taken into account; the cut-off date for submissions to the 2007 IPCC 4th Assessment Report was December 2006[66] and scientific papers cited in the IPCC's 4th Assessment Report had to be published or in press by December 2005.[67] Professor John Mitchell OBE, Director of Climate Science at the Met Office, acknowledged that there were concerns about the length of the IPCC process and the currency of the consensus it represented,[68] and argued that while it could validly base its recommendations on the IPCC assessments it should also look carefully at any new developments that stood up to scientific scrutiny.[69] Lord Turner said the Committee would look at the scientific evidence every four or five years and did not see any value in reviewing it every year.[70] The Committee on Climate Change will review scientific developments as part of the work that it will do to prepare its advice for the fourth budget period (2023-2027) to be published in 2010.[71]

29. Science will always run ahead of policy and it is a key part of the process that the scientific evidence base will be used to inform political judgements and decisions. Uncertainties are fundamental to all science and are not just a feature of climate science; other policy areas, like public health, face similar challenges. The Committee on Climate Change is right to use the IPCC's findings as a basis for its work. But they must keep scientific developments under review, first as part of the review that will be undertaken in preparing its advice on the fourth budget period, and second following the publication of the IPCC's 5th Assessment Report. The Government should provide the resources to allow the Committee on Climate Change to strengthen its scientific capability so that it can monitor developments in between these formal review points.

30. The need to review budgets in the light of new scientific developments must be weighed against the need for stability and predictability in the policy framework. Science has several times revised upwards the estimates of the extent of the temperature rise for a given increase in the concentration of greenhouse gases and the extent of the impacts of a given temperature rise. The constant message, and one that is entirely consistent with the Stern Review, is that the emphasis should be on reducing emissions as much as possible and as early as possible.[72] Notwithstanding that the IPCC reports currently represent the best consensus in the science the Committee on Climate Change and the Government should take into account that the growing evidence base for climate change impacts is reducing levels of scientific uncertainty, emissions are still growing and impacts are occurring faster and in more damaging ways than was previously thought likely. Both the Committee on Climate Change and the Government must be open to the possibility that as our scientific knowledge and understanding grows the case for taking action beyond the commitments we have already made will grow. There is a case for taking a more precautionary approach and adopting targets at the upper end or in excess of what is currently recommended by the IPCC.

AN APPROPRIATE LEVEL OF RISK?

31. The targets and budgets recommended by the Committee on Climate Change are designed to give about a 50:50 chance that temperatures will exceed 2°C by 2100, on the basis of the current state of scientific knowledge. The key question that needs to be addressed is whether it is possible to increase the chance of keeping any rise in temperature to below 2°C by cutting emissions faster.

32. Several witnesses suggested that it was possible to reduce the risk of exceeding 2°C.[73] The Institute of Actuaries' Resource and Environment Group argued that the level of risk associated with the Committee on Climate Change's recommendations was at least an order of magnitude higher than society would accept.[74] Friends of the Earth contended that the carbon budgets embodied too high a level of risk. They noted that the IPCC had defined levels of risk[75] and 'unlikely' was equated to a risk of 33% or lower[76] and a probability between 33% and 66% was regarded as 'as likely as not' on the IPCC's scale. The German Advisory Council on Global Change, using a global budget that had a 66% chance that warming could be kept below 2°C, came up with a much smaller available carbon budget.[77] The Global Commons Institute proposed a scenario for reducing emissions that it argued had better odds of keeping within 2°C than that proposed by the Committee on Climate Change.[78]

33. In the modelling done for the Committee on Climate Change, the Met Office examined several distributions of uncertainty for climate sensitivity and selected ones that tended to give a lower probability of staying under a 2°C global warming target.[79] Dr Jason Lowe, from the Met Office, argued that the choice of climate sensitivity meant the Committee on Climate Change's recommendations were based on an inherently precautionary approach.[80] Lord Turner said it was possible to devise a pathway that would limit the chances of going above 2°C to less than 20% but this would have produced targets which were not be politically achievable. Nor might such targets be a rational economic and political choice (that is to say that the world might be better off accepting a slightly greater degree of warming and then adapting to it).[81] He pointed out that "If you were to set the target as being […] a 99% certainty of not going above 2°C we would have to start dramatically de-industrialising today."[82] He was more concerned about keeping the risk of exceeding 3 or 4°C to very low levels than reducing the risk associated with exceeding 2°C.[83]

34. There are currently no credible ways to reduce emissions faster than the Committee on Climate Change has recommended. The Government should prioritise reducing the likelihood that temperatures will exceed 2°C down from a level that is 'as likely as not' to at least 'unlikely'. This is more important than aiming for a lower temperature rise target. In the meantime the Committee on Climate Change should continue to ensure that its advice is framed in terms of keeping the risks of exceeding 3 or 4°C to very low levels.

7 Committee on Climate Change, First Report of the Committee, Building a low carbon economy- the UK's contribution to tackling climate change, December 2008, p20. Back

8 University of Copenhagen, Synthesis Report from Climate Change: Global Risks, Challenges & Decisions, held in Copenhagen March 2009, http://climatecongress.ku.dk/pdf/synthesisreport Back

9 Q 228 Back

10 University of Copenhagen, Synthesis Report from Climate Change: Global Risks, Challenges & Decisions, held in Copenhagen March 2009, http://climatecongress.ku.dk/pdf/synthesisreport Back

11 University of Copenhagen, Synthesis Report from Climate Change: Global Risks, Challenges & Decisions, held in Copenhagen March 2009, http://climatecongress.ku.dk/pdf/synthesisreport Back

12 Q 2 [Hoskins] Back

13 University of Copenhagen, Synthesis Report from Climate Change: Global Risks, Challenges & Decisions, held in Copenhagen March 2009, http://climatecongress.ku.dk/pdf/synthesisreport Back

14 UNFCCC, The Copenhagen Accord, December 2009, http://unfccc.int/files/meetings/cop_15/application/pdf/cop15_cph_auv.pdf Back

15 Met Office, Four degrees and beyond, September 2009 Back

16 Ev 101 Back

17 Q 257 Back

18 Qq 228-229 Back