·       how thick the blanket of GHGs that surrounds the earth can be allowed to get in order to stay within the 2°C limit? In technical terms, at what level should GHGs be ‘stabilised’?

·       how much we need to cut annual GHG emissions by to keep it to that thickness?

·       and by what date emissions need to stop rising and start falling?

The thickness of the blanket – the concentration of carbon dioxide in the atmosphere – is now over 380 parts per million (ppm), having soared by about 25% in 200 years from below 300ppm where it had been for all of human history until the industrial revolution began and with it the burning of large volumes of coal, oil and gas and the destruction of vast areas of forests.

As a result of these activities, we are now pumping some 38 billion tonnes of GHGs into the air every year, thickening the layer of GHGs by about 2ppm annually (and last year saw a rise of 2.4ppm – tied as the record highest increase with 2005).  

Moving targets

The critical calculation now driving the debate is that made by the Intergovernmental Panel on Climate Change (IPCC), the body set up by the UN to answer these questions and advise policy-makers, in its 2007 report. The report said that to keep to a global rise in temperature of between 2°C and 2.4°C, the concentration of CO2 had to be stabilised at 350-400ppm – which means either below, at, or just above today’s level - with emissions peaking in 2015 or earlier and then being cut by 50 to 85% by 2050.

This represents a major toughening of the targets and timescales compared to previous estimates. For example when Robert Watson, the then chairman of the IPCC, addressed international negotiators in 2001, the scenario he highlighted was one in which governments would decide to stabilize the concentration of carbon dioxide at 550ppm, with emissions peaking around 2025.

In 2006, when Sir Nicholas Stern produced his report for the UK Government, he tightened the proposed targets, recommending that CO2 should be stabilised between 400 and 490ppm and calculating that stabilising GHG levels at the upper end of the range would require emissions to peak within 10 to 20 years. 

By 2007, Watson’s successor, Rajendra Pachauri, addressing the UN, pointed to the IPCC’s latest projection – the scenario in which CO2 had to be stabilised at 350-400ppm with emissions peaking in 2015 at the latest.  This has been taken up by others, including the former UK Prime Minister, Tony Blair, who has taken on the task of seeking to broker agreement between major players. He has repeated the message, saying “the IPCC says we must cut global emissions in half from 1990 levels with a peak in emissions by 2015 if we are to have a reasonable chance of avoiding a greater than 2 degree rise.”

Some go much further. James Hansen, Director of NASA’s Goddard Space Science Laboratories, believes it is necessary to take carbon out of the atmosphere and reduce the concentration of CO2 to 350ppm in order to preserve the Arctic’s sea ice and prevent catastrophic flooding.  He has also argued for limiting global warming to 1.7°C to avoid loss of polar ice, widespread flooding and large-scale species extinction. 

Feedback risks

Hansen and others point out that climate change is not simply a linear process in which a given level of emissions leads to a given concentration of GHGs and temperature rise. The climate is a complex system that has many feedback processes whereby one impact leads to another. For example, as ice melts, it loses its reflective quality, or ‘albedo’, and instead absorbs incoming heat, melting faster – a process called the ‘albedo-flip’.  Peter Wadhams, Professor of Ocean Physics at Cambridge University, has shown how the reduction in Arctic sea-ice measured each September – from over 8 million sq km in 1950 to close to 4 million now - is not only shrinking faster that the mean projection of earlier models, but faster that the lower limit of the standard deviation of the models – the ‘plus or minus’ that indicates the range of expected outcomes.

As tundra melts, for example in Siberia, there is a risk that vast quantities of methane, a much more powerful GHG than CO2, will be released. Many who study feedbacks believe that the focus on CO2 levels and temperature rises is too narrow and that climate change demands a more holistic ‘systems dynamics’ approach which embraces all elements of the world’s ecology.

David Wasdell, International Co-ordinator of the UK-based Meridian programme, has warned of a series of feedback effects, ranging from the albedo-flip and increasing methane emissions to increased volumes of water vapour due to increasing evaporation. He and others believe that the critical factor is the level of ‘radiative forcing’ – or heat – in the climate system – heat being to global warming what a gas burner is to a saucepan. Wasdell says that the key target is to push radiative forcing from its current level of around two watts per square metre down to zero. In his analysis, allowing the global temperature to rise by 2°C would be disastrous because it would entail approximately doubling the power of the heat engine and pushing the climate across a range of dangerous ‘tipping points’ including a major sea level rise. Wasdell therefore advocates moving immediately to a low-carbon, and then a no-carbon economy and then into a phase of carbon removal, using such measures as production of biochar, a form of charcoal that absorbs carbon as well as providing energy. 

An unprecedented challenge

Even if we leave aside these more radical warnings findings and recommendations, the IPCC scenario of stabilising CO2 at 400ppm with a peak in 2015 is an unprecedented challenge in itself. Take just the CO2 emissions from energy. These were around 27 billion tonnes (GT) in 2005 and they are currently expected to rise to at least 32GT in 2015 and at least 34GT in 2030 - according to the International Energy Agency (IEA) - and that is provided all currently proposed environmental policies are implemented.  

If the goal is to create a 2015 peak and a 50-85% emissions cut by 2050, then energy related CO2 emissions need to be cut to around 23GT in 2030, below today’s level and a third lower than current environmental policies would achieve. The IEA says this would require: “… immediate policy action and technological transformation on an unprecedented scale.”

Some countries might put a moratorium on coal fired power stations, coal being the worst culprit for emissions in the power sector. Others might offer much greater subsides for wind and solar power. Carbon taxes could be introduced, ramping up fuel and power prices. Huge grants and discounts might be offered on insulation, double glazing and all other ways of increasing energy efficiency. Nuclear plants may be accelerated – although their long lead times might mean countries having to ‘overdraw’ their carbon allowances until closer to 2020. Carbon capture and storage (CCS) – the technology that enables CO2 to be piped underground, virtually eliminating emissions from power stations and factories - may be accelerated. James Hansen has called for a global moratorium on coal plants that do not have carbon capture.

While many low or no-carbon options exist for power, transport presents major problems. Hybrid cars that run partly on electricity can help reduce emissions to a degree, but all alternative fuels have their own challenges. Hydrogen-powered vehicles appear decades away due to the costs and practical difficulties of manufacturing hydrogen sustainably and storing it in vehicles in sufficient quantities.

The biofuels in use today raise a series of issues. They tend to be blended into gasoline or diesel in low proportions, typically 5 or 10%, and so make little dent on emissions. But at the same time, they use food crops such as corn and wheat and have been seen as a cause of rising food prices.  Indeed it seems to many that the main function of today’s biofuels is not environmental at all, but to shift US fuel revenues from the Middle East to the mid-West. However the picture could change dramatically with the advent of next generation biofuels – such as those made from woody crops in which the whole plant is used. If these can be made economically, they hold out the promise of fuels that do not use food crops, have much higher energy content, can be blended in high proportions and avert large volumes of emissions.

There are also likely to be large-scale reforestation programmes and other actions to restore nature’s carbon sinks.  R&D programmes are likely to be stepped up to increase the efficiency of renewables, overcome obstacles to hydrogen-powered cars and investigate radical options such as new forms of geo-thermal energy and giant ‘concentrated solar thermal’ installations. 

The policy dimension

What policies will stimulate these programmes? Some of the changes will be incentivised by subsidies and taxes, but many countries are likely to follow the EU’s lead and introduce market-based carbon trading systems that set a limit or ‘cap’ on emissions from a group of emitters – which can be companies or countries – issuing participants with emissions allowances that together add up to the total. Participants who want to emit more than their limit have to buy allowances from others so the overall cap is not exceeded. Over time, the cap can be progressively lowered to reduce emissions.

It’s accepted that the developed world – which is largely responsible for the carbon in the air today - would need to accept deeper cuts than the developing world, where growth is strong but emissions-reducing technologies are less advanced.

However, the issue cannot be tackled without very deep cuts in the developing world as well - because since 2004, non-OECD emissions of carbon dioxide have been greater than those of the OECD countries, and the gap is growing.

Currently the ‘clean development mechanism’ of the Kyoto Treaty enables developed countries which help cut emissions in the developing world to count those reductions against their own targets. It’s likely that this mechanism would be expanded to provide one of the most important routes for cutting emissions.

Looking to the UK alone, regardless of obligations to help the developing world, the task is immense. In its 2007 report, the CBI proposed a series of measures it believed was needed to hit the current 60% GHG reduction target for 2050, with an interim objective of 40% by 2030. Its plans for 2030 included 3000 wind farms, 20 power plants using carbon capture and cars that are 40% more efficient than today’s. If that’s the prescription for the 60% target, what will it be if the world’s sights are set higher and the UK target rises to 80% or even more as a consequence?

‘Substantial costs’