The Climate Change Committee (CCC) wrote in its December report that the world could expect about a 2 degree rise in temperature by 2100 if global emissions fell by about 50% by mid-century. It said that the risk of more than a 4 degrees rise is less than 1% if the world achieved this reduction. Because the UK has per capita emissions much higher than the global average, the Committee recommended that the country should cut its emissions by about 80%. This would eventually leave the UK’s emissions per head as about the same as the rest of the world.

The CCC report is thorough, robust and clear. But is its recommendation sufficiently prudent? In four main respects, the Committee has chosen a more optimistic conclusion than I believe is warranted. The implication is that its emissions reductions targets are not severe enough.

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A grossly simplified model of climate change
The amount of global warming we can eventually expect depends on three key variables:

1. Emissions of greenhouse gases.
2. The percentage of these gases absorbed by ‘sinks’ such as the oceans, forests, and soils and thus extracted from the air.
3. The sensitivity of temperature to the total amount of greenhouse gas in the atmosphere.

Put another way, average global temperatures depend on the stock of greenhouse gases and the degree to which these gases heat up the atmosphere. Let’s look at the assumptions used by the CCC for each of these three variables:

1) Emissions of greenhouse gases
The CCC’s method was essentially to calculate numbers for 2) and for 3) and then to ask itself ‘What are maximum emission that can be allowed if the global temperature rise is kept to about 2 degrees?’ It found that if world emissions peaked in 2016 and then fell by 3% a year until 2050 the median expectation of temperature rise in 210 is about 2 degrees. This is essentially an arithmetic calculation that springs from the Committee’s assumptions about CO2 absorption and the sensitivity of temperature to levels of greenhouse gases.

2) The percentage of these gases absorbed by ‘sinks’ such as the oceans, forests, and soils and thus extracted from the air
Scientists have a general rule that in each year total absorption of carbon dioxide is slightly over 50% of the amount emitted. In other words, for every 2 tonnes of CO2 emitted every year, the total stock of carbon dioxide in the atmosphere rises about 1 tonne.

The relationship between the CO2 emitted and the amount absorbed is a complex one. Scientists say that if a single large ‘pulse’ of carbon dioxide entered the atmosphere the equivalent of 15-20% of this pulse would be typically absorbed within a year. Smaller and smaller amounts would be taken out in future years but almost a quarter would remain after several hundred years. Standard figures for how much carbon dioxide remains in the atmosphere (usually called the ‘airborne fraction’ or AF) are used in the runs of the immensely complex computer models employed by climate scientists. There can also be very substantial year-to-year variations in the AF because of such things as severe drought, which may result in low net CO2 absorption because of the dieback of vegetation containing carbon.

The predicted amount absorbed each year is a function of both the level and of the rate of change of emissions (sometimes called the trajectory). An increase in the rate of growth of emissions will typically produce a temporary increase in the amount of CO2 remaining in the atmosphere. This has happened in recent years and scientists have, as expected, noted a slow rise in the average AF. 2008 interrupted this trend because of the generally good growing conditions for vegetation, which increased the absorption of carbon dioxide.

Net CO2 added to the atmosphere as percentage of yearly emissions

The CCC’s projections show the AF falling fast from an expected peak in about 2011. By 2035, the atmosphere will add greenhouse gas emissions equivalent to only about 30% of the CO2 emitted each year. This change, in line with predictions by the standard models, means that for every tonne emitted in 2035 the net impact on atmospheric concentrations will be little more than half what it is today.

Net CO2 added to the atmosphere as percentage of yearly emissions (with CCC forecasts to 2035)

So where is the issue with the Committee’s projections? The problem is that the world’s ecosystems show increasing signs of not absorbing as much CO2 as they did in the past. The report acknowledges this in its text but does not appear to have included substantial weakening of the biosphere’s capacity to absorb carbon dioxide in its detailed forecasts. This raises the possibility that much more carbon will remain in the atmosphere than the Committee suggests. We cannot know with certainty that the forecasts from the CCC are wrong but we can suggest both that the ‘known unknowns’ and the ‘unknown unknowns’ are likely to reduce unexpectedly the total re-absorption of greenhouse gases.

A prudential approach might have employed more pessimistic assumptions about carbon uptake, with absorption declining more strongly over time. This recommendation is in line with the conclusions of increasing numbers of recent scientific papers.

3) The sensitivity of temperature to the total amount of greenhouse gas in the atmosphere
There is still considerable uncertainty about how much temperatures will rise in response to increased levels of climate changing gases. The uncertainty arises both from the imprecise understanding of exactly how much infra-red radiation (heat) is absorbed by carbon dioxide and other molecules and, second, from a lack of knowledge of how much the reflectivity of the earth is likely to change. Ice largely reflects visible light, which CO2 does not absorb as heat. But if ice melts, the surface underneath is darker (whether on sea or land). This reduces the reflection of light and increases the absorption of light energy by the surface. The absorption of energy results in higher levels of infra-red output eventually transmitted out to space, some of which is trapped by CO2.

The increase in temperature resulting from a doubling of greenhouse gas levels is known as the ‘climate sensitivity’. The Committee says that it uses a figure of 3 degrees Celsius in its work. Although this is not far from standard estimates, it is probably somewhat too low. The Fourth Report of the IPCC (2007) gives a figure of 3.26 degrees with a standard deviation estimate of 0.69 degrees. It may have been more appropriate to use this higher figure. In addition, the IPCC comments (p. 60 of Working Group III report) that:

Non-linearities in the feedbacks (including e.g. ice cover and carbon cycle) may cause time dependence of the effective climate sensitivity, as well as leading to larger uncertainties for greater warming levels.

The implication of this remark is that the distribution of probability of the future value of climate sensitivity is wider than we currently expect – there are more likely to be unpredicted extreme outcomes. The Committee might therefore have appropriately chosen a wider range of potential outcomes, as well as a higher median figure, for climate sensitivity.

Other issues
a) The median and the mean temperature rise
The Committee produced extremely detailed technical appendices. One spreadsheet looked at the distribution of expected temperature rise resulting from the various emissions trajectories modelled by the CCC. The Committee favours one scenario as meeting its requirements that the average figure for expected temperature rise is about 2 degrees. This scenario requires global emissions to peak in 2016 and then fall at 3% a year.

This outcome is said by the Committee to result in a distribution of possible temperature rises that is centred around 2 degrees. The chance of the actual figure being more than 4 degrees is less than 1%. The 2 degree figure has substantial totemic significance: most scientists and policy-makers see the world being able to cope with this rise, but with the risks of catastrophe rising sharply above this level.

The illustrative graphic below illustrates one problem with the CCC’s assessment. Its own assessment of the distribution of possible outcomes actually peak at 2.2 degrees. Secondly, the distribution has a larger area to the right of the median than it has to the left. The ‘central model estimate’ of temperature rise is 2.2 degrees, but this is not the average increase we can expect. There is a larger chance of outcomes to the right of the 2.2 degrees than there is to the left. The actual average figure (which is the statistical mean of this distribution) is about 2.3 degrees. It seems a small change but in climate science tenths of one degree are important.

In this case I think it would have been prudent to state that the mean temperature rise expected under the Committee’s projections is 2.3 degrees. The report should have stressed that this figure is substantially different from the 2 degree level which the CCC indicates is an important line to hold.

Schematic representation of the distribution of temperature rises by 2100 under the CCC’s 2016 3% p.a. reduction scenario

b) Overshooting
The CCC’s proposed global emissions trajectory and its assumptions about AF show greenhouse gas concentrations rising to about 500 ppm and then slowly declining. If concentrations stayed at 500 ppm, the mean expected increase in temperature would be higher than the Committee forecasts. (As it stands, even the Committee’s own figures see temperatures peaking under the ‘3% p.a. from 2016’ scenario at over 2.6 degrees above pre-industrial levels sometime well after 2100.)

The CCC is recommending what the climate science trade calls ‘overshooting’ or letting greenhouse gas concentrations rise to above a certain level and then reducing them to what might be called a ‘safer’ number. Underlying this recommendation is, in effect, a belief that we can rely on lags in the climate system. The climate will, as it were, not ‘notice’ the temporary higher levels of climate changing gases, largely because the oceans will absorb the extra heat for at least a few decades.

‘Overshooting’ has some supporters. But the CCC’s predecessor, the 2006 Stern Review, took a dim view of this tactic:

An overshooting path to any stabilisation level would lead to greater impacts. [...] Overshooting is potentially high risk. (p. 228 of the printed edition)

The CCC acknowledges that overshooting has potential perils. But it goes on to say that not overshooting would increase the required reduction rate from 3% from 2016 to almost 7% a year. Understandably, it sees this sharper cut as more difficult to achieve. Nevertheless, a more prudent approach would have pushed the Committee towards recommending that the UK government adopt a tighter emissions reduction regime than it actually specifies in its report.

Why do we want a more prudent approach?
Loosely speaking, this article notes four areas in which Committee showed limited risk aversion in its recommendations. It may be right to have done this. However, as climate science progresses it seems to be increasingly telling us that the probability distributions of expected ‘climate sensitivity’ and of annual rates of CO2 absorption by sinks are widening. In other words, our assessment of the risks from climate change should be rising. We should be incorporating more risk aversion, not less, into our policies.

The CCC itself admits that the climate science is worryingly pessimistic. At one stage, the report acknowledges one recent paper that suggests that the world is already locked into a temperature rise of 2.4 degrees because atmospheric aerosol pollution is masking the underlying existing impact of greenhouse gases. Having mentioned this particular scientific work, it then seems to have largely ignored the implications.

This could be a completely unfair criticism of the CCC’s approach. The Committee may, quite rationally, have said to itself that the political elite can only be dragged slowly into accepting the need for rapid decarbonisation of the economy. A more pessimistic conclusion from the CCC’s December report might have made policy-makers despair and thus actually reduced the likely rate of change. But the rest of us Jeremiahs need to keep the pressure up for commitment to even faster rates of progress.

Photograph: Christopher Thomond. Source: Guardian.

The new Conservative policy document on energy is keen to emphasise how smart it is. At its core are proposals for smart meters, smart grids, and smart battery charging. The enthusiasm for these technologies is almost palpable. On one page, the word ‘smart’ occurs eight times. But readers of the policy proposals are largely left in the dark about what all these intelligent devices will do. David Cameron’s comments about building ‘an electricity internet’ didn’t shed much light either.

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So let’s give an example of how these technologies might work. Last Saturday evening was windy. A westerly gale meant that almost every wind turbine in the UK would have been producing close to its maximum output. If wind power continues to expand rapidly, Britain will eventually have a surplus of electricity on some winter days. On these occasions, we will need what is known as a ‘smart grid’ to help deploy the extra electricity elsewhere in Europe. While the wind was blowing hard across our westerly coasts at the weekend, large parts of the Continent were calm and could have usefully imported our surplus. Forecasts suggest that eastern Europe will see higher wind speeds later in the week, when the weather in Britain has calmed down. In these circumstances a smart European grid would redirect power back towards the British Isles. During periods of high wind speeds in the UK ‘smart meters’ in people’s homes will signal the abundance of power, offering consumers discounted prices to use the surplus electricity. In 10 or 15 years’ time, it is not fanciful to say that many householders will use these periods of cheap power to recharge the batteries in their electric cars. This is the third leg of the Conservative proposals: ‘smart charging’.

In a world where intermittent renewables form a larger and larger part of energy supply, countries will need to link their grids to allow the export and import of huge quantities of electricity at short notice. At the moment, our link to the French electricity system gives a buffer of only about 5% of our power consumption. The Conservatives are right to emphasise the importance of changing this. Multiple new high-voltage lines will be required to move power from where it is in surplus to where it is in deficit. We will need to invest heavily in the storage of energy so that we can cope with transitory shortages of supply. The UK must also have a major investment in new high-voltage lines to bring power from wind and tidal farms in Scotland down to the south of England, where the electricity is in greatest demand.

What the Conservatives don’t tell us is how these huge investments of many tens of billions of pounds are going to be financed. The UK has a problem – its electricity distribution system is privately owned. National Grid is a public company, responsible to shareholders. It provides access to its existing network of high-voltage transmission lines in return for regulated fees paid by the six large electricity supply companies. Whether or not the UK gets the new smart grid infrastructure in place to move electricity around Europe at 10 minutes’ notice is entirely dependent on whether National Grid thinks it is profitable to make the investments. We cannot be too optimistic about this. Many large Scottish wind farms have not been built because the operators are unable to connect the turbines to the high-voltage pylon network.

The material on smart meters is similarly vague. These meters, under the stairs or in outside cabinets, contain a little transmitter that sends energy consumption data every 30 minutes back to the electricity supplier. Small wireless displays in the hall or the kitchen also show householders how much gas or electricity that they are using. These systems are expensive; Landis + Gyr, a major supplier of these devices, told me that the cost for gas and electricity may be as much as £10bn, or almost £400 a home once the costs of fitting the meters is included. A report from the leading economics consultancy Frontier put the figure at a slightly lower level. In Britain’s liberalised energy markets it is unclear who should pay for this expense and the Conservatives give us no clue how they think the bill should be apportioned. In fact, the cost of this scheme is never even mentioned.

The policy paper says that smart meters incentivise people to cut back on their energy consumption by providing real-time information on utility bills. This is probably true. Some early studies using enthusiastic volunteers have shown cuts in electricity of 5% or more, perhaps worth £30 a year at today’s prices. But the report by Frontier Economics suggests a much smaller figure of one or 2%, implying trivial savings to the householder.

Despite what the Conservatives suggest, the real benefits are likely to be considerably more controversial. Smart meters allow suppliers to change prices to encourage us to cut back or to increase energy consumption. Electricity use goes through predictable daily swings, falling to a low point at about 5am and rising to an early evening peak. Smart meters can be used to price electricity to deter the use of appliances at times of high demand when electricity tends to be most expensive to produce, something that can be very helpful in reducing carbon emissions and improving security of supply. Experience from around the world shows that smart meters and differential pricing can make substantial differences to energy consumption. But not everybody likes these changes – we’ve got used to turning our appliances on and off without worrying about the time of day.

In addition, suppliers can use smart meters to introduce emergency restrictions on electricity consumption at times of unexpected shortage. If the wind suddenly drops or a nuclear power station fails the smart meter can temporarily ration a household to one or two kilowatts, enough for lights and the TV but not for the vacuum cleaner. This aspect of smart metering is nowhere mentioned in the Conservative paper. In line with Conservative philosophy, people are reassured that participation in the smart meter programme will be entirely voluntary. Elsewhere in the world governments have always decided that advanced metering will only work if it is almost universal. I know of no other country intending to make participation a matter of householder choice. This will substantially reduce the effectiveness of the programme. Who will join in if they think it will increase their electricity bills or restrict their access to power?

Smartening up our supply and use of electricity is an important aim – and the Conservatives are right to pull this issue into the public debate. However, their proposals are completely uncosted. This is a problem throughout the document; for example, they tell us that covering a roof with 40 square metres of solar panels will provide the typical household with enough electricity to cover its annual consumption. Nowhere do they say that this will cost at least £25,000 and probably more. Moreover they consistently fail to specify how their proposals can be implemented within today’s entirely privatised energy markets. Plans for smart metering in the UK have already been bogged down in arguments between Ofgem and the big six energy suppliers for almost five years. The Conservatives give us strikingly little detail on how they propose to clear this log-jam. Their heart is in the right place, but they have still to fully understand how the privatisation of the electricity supply system 15 years ago may now make modernisation of our energy infrastructure almost impossible.

This article was originally published in the Guardian on Monday 19 January 2009.

A powerful US coalition of large industrial companies, power producers, and environmental defence organisations has produced the first sensible plan for incentivising the early introduction of carbon capture at solid fuel electricity plants. The scheme proposed by the US Climate Action Partnership (USCAP) addresses the most important environmental issue in the world – the burning of coal to generate electricity – in a plausible and coherent way. Coal, which is almost exclusively burnt in power stations or in steel-making, is responsible for about 36% of US emissions. If we can find a way of cheaply capturing the CO2 from power stations and storing it underground, we can then also provide the technology to Chinese and Indian generators.

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The key points are as follows:

1. The cap and trade scheme that the new US administration is likely to implement may not produce a carbon price that is high enough to force coal-fired power stations into CCS. Therefore CCS may need a special financial regime.
2. USCAP says the US should pay power stations to sequester carbon. Payment should be highest for the first power stations to fit CCS equipment. The proposal suggests that $90 a tonne is sufficient to incentivise the first 3 gigawatts of power capacity to switch to using CCS. 3 gigawatts is approximately the power output of two large power stations such as Didcot A in the UK.
3. The paper states that $90 a tonne is enough to cover the costs for the first projects. This statement is hugely encouraging because it is lower than many people expect. USCAP has members that operate coal-fired power stations so the number will not have been lightly chosen. Expressed in terms of cost per megawatt hour, the proposed payment is perhaps $80-$100, depending on the age of the plant. For comparison, UK baseload power prices are currently about $80 an hour. Prices are much lower in the US. Once 3 gigawatts of CCS plant have been installed, the report proposes that the price per tonne drops. The scheme therefore provides the highest incentive to the first-movers.
4. A floor price of $30 is suggested for years 11 to 20 of the scheme. Let’s be absolutely clear: if we can actually get coal CO2 sequestration for $30 a tonne, then CCS is a viable technology. If we could decarbonise the entire UK economy for this price (i.e. not just coal-fired electricity generation), then the cost would be about 1% of GDP.
5. USCAP proposes that all new payments should stop once 72 gigawatts of power generation with carbon capture has been installed. This is about a quarter of current US coal generation capacity. This further incentivises operators to move quickly down the CCS road.

Other steps

6. Financial measures need to be accompanied by a national programme of R+D on geologic storage and CO2 pipeline networks. (A skeleton CO2 pipeline infrastructure already exists in the US.)
7. Quantitative restrictions. In addition to the CCS proposals, USCAP says that:
   • a) All new power stations should have to pay for their carbon allowances.
   • b) Tightening restrictions should be placed on all new power stations from 2015 onwards. I suspect that the levels proposed would only be achievable using what is loosely called ‘clean coal’ technology, probably the largely unproven IGCC approach (Integrated Gasification Combined Cycle – the coal is gasified and then burnt in a turbine). IGCC ought to be able to achieve emissions levels not far above today’s natural gas power plants and within the 800lbs (less than 350kg) CO2 per megawatt hour proposed as the cap in 2020.

Taken together, this package of proposals is a sensible way of paying power station owners to invest quickly in CCS. The levels of payment that are suggested are much lower than most people believed were possible.

The UK and other countries must take note of this package. It is a very much better set of proposals than any European scheme because it creates pressure for power station operators to start to push CCS now. In the UK, by contrast, the generators are sitting on their hands waiting to see how much they can extract in direct subsidy from government. A further advantage of the US scheme is that it provides limited reason for the inventor of any technology to restrict other generators from using the successful approach.

The rest of the extremely sensible package of proposals from USCAP can be found at http://www.us-cap.org/.