Energy, CO2 stabilisation and economic growth

Peter Smith, Nottingham University, looks at the scale of changes that are needed in energy production to tackle climate change.

Article from joint SGR/ AESR Newsletter, February 2005

At present we are where the Intergovernmental Panel on Climate change (IPCC) hoped we wouldn't be by this time, that is, with a concentration of ~380 parts per million (ppm) of CO2 in the atmosphere. So, where do we go from here?

Since the 1990 IPCC report most of the world has adhered firmly to the ‘business as usual' scenario. If we continue on this course until the latter part of the century, atmospheric concentrations could reach 750 – 1000 ppm, judging by levels of CO2 in 2003. In that year the rate of increase made a massive jump to ~3ppm per year. The IPCC is now saying that our only chance of avoiding possibly catastrophic climate change is to stabilise at no more than 550 ppm by 2025. This is endorsed by the Hadley Centre at the Met Office.

It's not only a matter of stabilising at 550 ppm but also of reducing it to well below the present level by 2100. Is this realistic, bearing in mind that primary energy consumption will rise inexorably during this century? There are those who think we can under certain conditions. The scenario which follows makes a number of assumptions based on the IPCC:

  • That the current rate of decrease in primary energy intensity (the amount of energy consumed per unit of GDP) would be maintained to the end of the century.

  • That the present rate of decline in the carbon intensity of energy (the amount of carbon released per unit of energy consumed) would also continue to 2100.

The first refers mainly to the demand side; the second to the supply side of the energy infrastructure.

A third assumption needs to be made regarding the growth in demand for primary energy as the developing nations maintain their rates of economic growth, most notably China, and access to electronic goods escalates. One estimate in a paper by D W Aitken, L L Billman and S R Bull, is that world energy consumption will increase from 380 exajoules (EJ) per year in 1990 to ~1400 EJ in 2100 [1].

The first two assumptions concerning primary energy intensity and carbon intensity impinge directly on the energy efficiency of the built environment as the sector most implicated indirectly in emissions of CO2 . Maintaining the rate of improvement in energy conservation since 1990 is a formidable challenge. So also is the expectation that buildings will become a major platform for embedded energy, mostly from solar photo-voltaics (PVs). This will be realistic as soon as PVs become cost effective.

However, the stark fact is that, bearing in mind the slow response time and self-interest fixation of human nature, our salvation will not lie with the demand side but the supply side. According to a paper in New Scientist “Simple measures like improving energy efficiency would help, but they would not be nearly enough. To ensure we add no more carbon to the atmosphere than we take away will require major structural changes to the global energy industry” [2] . The decarbonisation of primary energy is the key to the stabilisation of atmospheric carbon at a level which, hopefully, will keep climate related damage within remedial limits in the short to medium term. That level is a peak of 550 ppm by 2025 according to the IPCC and declining thereafter.

The next question is: what rate of installation of renewable energy, excluding hydro and nuclear, will be needed to reach this ceiling and then cause the concentration to decline? This is an impossible question to answer because it not only involves the decarbonisation of energy but also in parallel the sequestration of atmospheric carbon by reforestation etc. However Aitken et al make a case which at least gives a picture of the scale of the problem we face [3].

They recommend a scale of contribution by renewables as:

•  16 – 19% by 2010 rationalised as 10%

•  21 - 26% by 2020 rationalised as 20%

•  30% by 2030

•  50% by 2050

•  80% by 2100.

The next job is to translate these percentages into actual energy.



total energy

contribution by renewables



757 EJ

227 EJ



946 EJ

473 EJ



1400 EJ

1200 EJ

To give an idea of the scale of the challenge the 550 ppm target would require an installation rate worldwide of 920 MW per day until around 2050. If there was slippage and the target was raised to 750 ppm even this would necessitate 450 MW of non-hydro power installed per day.

One country which is on course to endorse this scenario is not the UK but Germany (Figure 1).

The Aitken paper gives an estimate of the breakdown of renewables technologies which will contribute to the 80% target by 2100 (Figure 2). This spread would not apply to the UK which enjoys massive power potential from its marine environment. Tidal energy alone could deliver ~60GW.

Academic exercises like this are all very well, but is there the remotest chance that the world can produce 1200 EJ of carbon neutral energy? Two further question arise from this. First can renewables produce this amount of energy in total? Second, if yes, can they expand at the rate needed to ensure that CO2 stabilises at not more than 550ppm? This is a question that can remain open. But not for long.

Considering the amount of solar radiation that reaches the Earth it seems logical that ultimately enough energy will be harnessed from this to meet the expanding needs of human society.

There are some who will question the urgency. The reason has been encapsulated in a graph from the IPCC which predicts the long term effect of an increase in atmospheric CO2 (Figure 3).

If emissions concentrations exceed 450ppm the temperature will continue to rise for centuries. Sea level also will continue to rise through a combination of melting ice and thermal expansion well into the fourth millennium, even assuming that anthropogenic CO2 will ultimately be virtually at zero.

In this scenario things don't look good for the Arctic , the Greenland and West Antarctic ice sheets which could all melt with the persistent rise of temperature leading to a sea level rise of 5 – 12m.

But that's not all. New uncertainties emerge almost by the month. A recent workshop at the Hadley Centre considered the effect of cloud formation on global warming. Cloud cover is falling and the reflectivity of the clouds plays a major part in controlling the radiation reaching the earth. James Murphy of the Centre presented a graph to the workshop which showed that resulting positive feedback could produce peak temperature rises of 6, 8 or 10ºC. David Stainforth of Oxford University suggested the possibility of 12ºC.

The outcome of this is that James Murphy has revised the standard bell curve showing the predicted extent and probability of global warming. Adapting climate models to take account of these uncertainties produces a ‘tail' extending to 12ºC, albeit at a low probability (Figure 4).

There is also the problem of high level pollution by particulates from the burning of fossil fuels, forests and crop waste. In the upper atmosphere these create aerosols which have the effect of reducing the solar radiation to the Earth. The ‘parasol effect' “could be disguising between half and three quarters of present warming” [4] . Crutzen's estimate could raise the estimate of warming under the 550ppmv scenario to 7 – 10ºC (Figure 5).

Another uncertainty is the carbon stored in the world's peat bogs which is said to be leaching into the atmosphere at an alarming rate. On one estimate the peat bogs of Europe , Siberia and North America hold the equivalent of 70 years of world industrial emissions. Feedback is operating here in that increased levels of CO2 in the atmosphere accelerate the release of carbon into rivers as dissolved organic carbon (DOC). Bacteria in rivers rapidly turn the DOC into CO2 that is released to the atmosphere. Researchers at Lancaster University have found that DOC levels in rivers in the Welsh mountains have increased by 90% since 1988 [5] . The verdict of Chris Freeman of the University of Wales at Bangor is that “by the middle of the century, DOC emissions from peat bogs and rivers could be as big a source of CO2 to the atmosphere as burning fossil fuels” [5] .

Global warming is melting snow, ice caps and mountain glaciers, exposing bare rock, tundra and open water causing the Earth's surface to absorb more radiation from the sun. This positive feedback loop is already in evidence in the Arctic where warming is happening five times faster than the global average. Also, as the world warms so there is greater evaporation from lakes and oceans. Water vapour is a powerful greenhouse gas. Taken together the scientific opinion is that the reduction in the albedo effect could add a further 3ºC to warming.

The conclusion of all this is that there is much greater urgency to take radical action to curb CO2 emissions than is generally acknowledged by governments. Actions we take now, or avoid taking, will have repercussions for centuries to come, and the speed at which we take radical measures to reduce carbon emissions will have major implications for the state of the planet by the year 3000. A delay of decades now could substantially amplify the ultimate effects of global warming. The situation has all the potential to be a tragic demonstration of the butterfly effect.

A scenario for the United Kingdom

In 2003 the UK consumed 233 million tonnes of oil equivalent (mtoe) or 8.75 EJ of energy, including transport. The object is to assess the rate of installation of renewable energy which will be required under the 20-30-50-80 scenario within the context of rising consumption.

In making long term predictions for the UK it is reasonable to assume that, in line with the world prediction, energy consumption will rise at least until 2100. In 2003 final energy consumption rose on average by 2%. In the year 2003–4 the total final energy consumption rose by 2.8% [6] .

For the purposes of this study it is assumed that energy consumption will rise at an average rate of 1% per year up to 2100 due to continuing economic growth, particularly with regard to transport. This is the net increase after all the demand side reduction measures have been taken into account.

The position of the UK with regard to CO2 abatement received a large boost from the switch to gas generation sharply revealed in the DTI histogram (Figure 6) showing the sources of energy in 1970 and 2002. It also indicates that energy consumption rose from 210.1 to 229.6 mtoe. This switch to gas is particularly prominent in the production of electricity between 1990 and 2002. This fact, combined with the decline in heavy industry, accounts for almost all the CO2 savings which are being claimed.

The breakdown of consumption for 2002 in mtoe was:



Domestic sector






In addition there were conversion losses of 52.4 and distribution losses and energy industry use of 19.9 mtoe. The temperature corrected total for 2002 including transport was 235 mtoe.

Figure 7 highlights the change in fuels for generating electricity between 1990 and 2002.

The long term assumption in the UK scenario is that energy consumption will rise at an average of 1% per year up to 2100 due to continuing economic growth. This is the net increase after all the demand side reduction measures have been taken into account. This has implications for the targets which the Government has set for CO2 abatement of 60% against 1990 levels by 2050. The scenario used here employs the Aitken et al model of 20% by 2020, 30% by 2050 and 50% by 2050.

Now that this initial benefit has been ‘spent', UK emissions are again rising.

A combination of depleted resources and price volatility will probably drive transport increasingly to switch to hydrogen as a fuel, first as a direct fuel and then to power fuel cells.

If it is assumed that the current average conversion efficiency is 25% for all UK transport and 50% equivalent for hydrogen, then the equivalent requirement to 54 mtoe of fossil fuel would be 27 mtoe of Hydrogen or 1.1 EJ of renewable electricity. This comes well within the estimated renewable requirement even when reasonable transport growth is factored in. Starting from the UK energy consumption of 235 mtoe in 2002 and incrementing 1% per year, total energy predictions and renewable energy targets to 2100 would be:



total energy EJ

renewable energy EJ




(281 mtoe)


(56 mtoe)




(310 mtoe)


(93 mtoe)




(379 mtoe)


(189 mtoe)




(623 mtoe)


(498 mtoe)

The stark conclusion is that the contribution from renewable sources in 2100 will need to be well over twice the total energy expended in the UK in 2004. Even by 2050 it will be close to the current total level of 233 mtoe. This highlights the scale of the problem facing the developed countries if CO2 is to be stabilised at less than the critical tipping point of 550ppm.

At the present state of the technologies, renewable systems could provide ~200 GW of energy from both marine and land based installations [8] . This still leaves a significant energy gap once we factor in transport energy. The UK has the potential to produce biofuels but these will be competing with food crops as it becomes less and less acceptable to import food from long distances. Hopefully some of the technologies being developed to produce large quantities of hydrogen at low cost will become market ready within a decade. Nanotechnology may well provide the answer to the safe hydrogen storage in vehicles.

So, no more procrastination through committees of inquiry, long-life research projects etc. The first priority is to reconfigure the grid to enable it to receive power from small-scale distributed generators. Then it must become cost effective (as in Germany ) for householders to install photovoltaics, small scale wind and solar thermal systems. At the very least there must be free installation of net metering on demand. At the same time there must be investment in GW scale renewable technologies like tidal and not wait until 2020 before considering anything other than wind.

We know most of what we need to know and could proceed with widespread implementation, unless, that is, the government continues to be fixated on the so-called free market. There has to be a large insurance premium to be paid for the long term security of the planet and this will not be forthcoming if things are left to market forces. That would be the superhighway to what the IPCC has called “future large scale and possibly irreversible changes in Earth systems” in other words runaway global warming.

Peter F Smith MA (Cantab) PhD (Manc) FRIBA FRSA, is Special Professor in Sustainable Energy, University of Nottingham


1. The climate stabilisation challenge. Renewable Energy World, Nov-Dec 2004 pp6 – 69.

2. Kyoto won't stop climate change. Fred Pearce. New Scientist, 9 Oct 2004 , pp6-7.

3. IPCC and James Murphy, New Scientist, 24 July 2004 , p45.

4. Paul Crutzen, New Scientist, 7 June 2003 , p7.

5. New Scientist, 10 July 2004 , p9.

6. Energy Trends for December 2004. DTI.

7. UK Energy in Brief, July 2003. DTI.

8. Smith P. A scenario for fossil and nuclear-free electricity for the UK . AESR newsletter, June 2004, pp1-5.


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