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However, UK decreases are dwarfed by global increases. After no-growth years in 2016 and 2017, global carbon dioxide emissions grew by 3% in 2018 (Figure 8b). European emissions fell but the growth in all the other parts of the world was 17 times greater. The emissions reductions in the UK have also come at a considerable cost. Figure 9 shows the increasing deficit of the UK balance of payments with respect to manufactures since then. In other words, a significant proportion of our emissions have been exported to China and elsewhere. Indeed, over the period 1991– 2007, the emissions associated with rising imports almost exactly cancelled the UK emissions reduction!

Figure 9: UK deficit in manufactured goods

Some of the measures introduced by the Climate Change Committee have actually made global emissions worse. Where we once smelted aluminium using electricity generated from a mixture of nuclear, gas and coal, we now import our aluminium from China where electricity is nearly all made from coal. What is worse, the smelter in Anglesey had a contract to use more electricity when the local demand was low (at night and on weekends); costs were kept lower for everyone. Now the smelter has gone, local consumers have to pay more for their electricity as the generators are less efficiently used.

There was much publicity in late summer this year when 50% of the UK’s electricity was (briefly) generated from renewables. Few people realised that electricity is only 16% of our total energy usage, and it is a common error, even in Parliament, to think that we are making enormous progress on the whole energy front. The real challenge is shown in Figure 10, where the energy used in fuels, heating and electricity are directly compared over a three-year period. Several striking points emerge from this one figure. First, we use twice as much energy in the UK for transport as we do for electricity. Little progress has been made in converting the fuel energy to electricity, as there are few electric vehicles and no ships or aircraft that are battery powered. Note that if such a conversion of transport fuel to electricity were to take place, the grid capacity would have to treble from what we have today. Second, most of the electricity use today is baseload, with small daily and seasonal variations (one can see the effect of the Christmas holidays). The more intermittent wind and solar energy is used, the more back-up has to be ready for nights and times of anticyclones or both: the back-up capacity could have been used all along to produce higher levels of baseload electricity, and because it is being used less efficiently, the resulting back-up generation costs more as it pays off the same total capital costs. But in fact it is the heating that is the real problem. Today that is provided by gas, with gas flows varying by a factor of eight between highs in winter and lows in summer. If heat were to be electrified along with transport, the grid capacity would have to be expanded by a factor between five and six from today. How many more wind and solar farms would we need?

Figure 10: UK energy demand by type over three annual cycles


Germany is often held out as the European leader, with over e800 billion invested in the ‘Energy Transition’. However, as in the UK, electricity is a small fraction of German energy demand, and despite the vast expenditure, only about one seventh of total energy supply is currently from renewable sources. Meanwhile, reductions in carbon dioxide emissions have been proportionally less than in the UK in recent years, in part because Germany has maintained more of its industrial manufacturing base. Germany’s renewables leadership has mostly been in demonstrating the difficulties of using renewables on the grid. The successes of renewables are usually reported in summer when electricity demand is at its lowest. But in winter, when the solar panels are covered with snow and there are week-long anticyclones, the German grid gets very little electricity from renewables. Indeed, over the winter of 2016–7 there were two periods, each of ten days, when little or no renewable energy was generated. Germany’s power storage capacity – mostly hydroelectricity – was woefully inadequate to meeting this shortfall. Total electricity consumption in both of these periods was 800 times what dams could store and generate. This is not atypical in developed countries. The total pumped storage capacity in the USA would run its grid for three hours, while the installed battery storage would run it for five minutes. Consumers in Germany have paid a high price for this leadership too. An electricity grid with high penetration of renewables is necessarily inefficient because of the intermittency and unreliability of wind and solar power. German electricity prices are among the highest in the world.


To conclude this section, Figure 11a shows that renewables are not even close to meeting the growth in demand, let alone reducing existing levels of fossil fuel use. Renewable energy’s contributions remain small compared with fossil fuels in relative terms, even if in absolute terms they are large compared with values elsewhere in the world. The forward projections show a constant value of coal and gas used for electricity through to 2040.

Figure 11: Fossil fuels are driving China’s growth

China’s carbon dioxide emissions have been rising inexorably, with little sign of a slowdown (Figure 11b).

Initial conclusions

So far, I have described the scale of the global energy sector, how it has come to be the size it is, the current drivers for more energy and the current status of attempts to decarbonise the global economy. I can draw some initial conclusions at this point.

  • Energy equals quality of life and we intervene there only with the most convincing of cases.
  • Renewables do not come close to constituting a solution to the climate change problem for an industrialised world.
  • China is not the beacon of hope it is portrayed to be.
  • There is no ground shift in energy sources despite claims to contrary. For the rest of this lecture I shall delve further into engineering issues.

The engineering challenges implied by factors of hundreds and thousands

Many people do not realise the very different natures of the forms of energy we use today. But energy generation technologies can differ by factors of hundreds or thousands on key measures, such as the efficiency of materials use, the land area needed, the whole-life costs of ownership, and matters associated with energy storage.

Here are four statements about the efficiency with which energy generation systems use high-value advanced materials:

  • A Siemens gas turbine weighs 312 tonnes and delivers 600 MW. That translates to 1920 W/kg of firm power over a 40-year design life.
  • The Finnish PWR reactors weigh 500 tonnes and produces 860 MW of power, equivalent to 1700 W/kg of firm supply over 40 years. When combined with a steam turbine, the figure is 1000 W/kg.
  • A 1.8-MW wind turbine weighs 164 tonnes, made up of a 56-tonne nacelle, 36 tonnes for the blades, and a 71-tonne tower. That is equivalent to 10 W/kg for the nameplate capacity, but at a typical load factor of 30%, this corresponds to 3 W/kg of firm power. A 3.6-MW offshore turbine, with its 400-tonne above-water assembly, and with a 40% load factor, comes out at 3.6 W/kg over a 20-year life.
  • Solarpanels for roof-top installation weigha bout 16kg/m2,and with about40W/m2 firm power provided over a year, that translates to about 2.5 W/kg energy per mass over a 20-year life.

The figures are shown in Figure 12, although the wind and solar bars are all but invisible.

Figure 12: Power-to-weight ratios for various generation technologies

Now the gas turbines and nuclear power stations need fuels, but these are not subject to energy-intensive processing in the way that steels, silicon wafers and fibre-composites are. Moreover, in the case of wind, I have not mentioned the plinth, which is comparable in size to the one required for a combined cycle gas turbine or nuclear reactor, but you’d need 360 5-MW wind turbines (of 33% efficiency) to produce the same output as a gas turbine, each with concrete foundations of comparable volume. The concrete requires high-energy processing of large quantities of cement, and the plinths must be removed at the end of life.

The requirement for land is another consideration. Both wind and solar energy are intrinsically more dilute than fossil fuels, in which past sunlight has been concentrated many times over, or nuclear fuels where the nuclear energies involved are much greater than the chemical energies in fossil fuels which are in turn much greater than the solar and wind energies.

The late David MacKay showed that the land areas needed to produce 225 MW of power were very different: 15 acres for a small modular nuclear reactor, 2400 acres for average solar cell arrays, and 60,000 acres for an average wind farm (Figure 13).

Figure 13: Areas required for different 225-MW power stations

My own example takes the 4000 km2 of the Fen country, currently used to provide some of the food for London. If it was used instead to grow miscanthus grass, year-round, to be harvested and burned to drive a steam generator for electricity, one would get 2 GW of continuous electricity. However from a land area of 0.1km2 (300m by 300m), the Sizewell B nuclear reactor produces 1.3 GW continuously. The ratio of land areas involved is 40,000 to 1! Note that if state-of-the-art solar panels were used, the ratio of land needed to produce the same electricity continuously is 1000:1. Land in the UK is too highly valued, even as a rural amenity, to be given over to wind turbines or solar panels.

Technologies for storing energy are also very different. Table 1 shows the energy density of different fuels. The ratio of energy stored per kilogram between lead-acid batteries, modern lithium-ion batteries and petrol are as 1:6:273. Despite the need for better batteries since electronics first became mobile in the 1970s, the improvement after decades of intense research has been from zinc-carbon batteries, with comparable energy density to lead-acid, to modern lithium-ion technologies, which are six times denser. There are no prospects of taking on petrol, which still has over 40 times greater energy density. The reasons for this are clear: the energy in most bonds is available when petrol is burned, whereas the energy of only a limited number of electrons (typically one per atom in the anode volume) can be accessed per discharge cycle in a battery.

Table 1: Energy densities of different fuels

Technology Energy density MJ/kg

 Wind turbine  0.00006
 Lead-Acid Battery  0.15
 Hydro  0.72
 Wood  5
 Petrol  50
 Hydrogen  143
 Nuclear Fission  88250000
 Nuclear Fusion  645000000

Source: M J Kelly, ‘Lessons from technology development for energy and sustainability’

MRS Energy and Sustainability 2016; 3: 2–13.

The productivity of renewables

If a cheetah exerts more energy chasing a rabbit than it gets by eating it, its future is not assured. If the cheetah is supporting a family, then the ratio of energy expended to energy obtained had better be much less than unity. A similar calculation can be performed for energy generation technologies. This is known as the energy return on investment. The solar farms installed in Spain during 2006–9 expect to collect 250% of the energy used in their manufacture, installation and operation over their 25-year lifetimes, so in energy terms or money terms, the return on investment is 2.5:1. If the panels were free and their efficiency up 50% on the actual solar panels of a decade ago (reaching the absolute limit imposed by the physics of solar interactions with one semiconductor interface), the EROI rises to about 5:1. Data from the first-of-its-kind wind farm at Vindeby shows that the lifetime revenue is only 140% of the construction cost, reduced to 100% when lifetime maintenance costs are added. For the Hornsea 1 offshore windfarm, due to be completed next year, the expected lifetime revenue is only five times the total lifetime costs. The figure for the Hinkley Point nuclear power station is 7:1, or more if there is any life extension as is common with nuclear power plants.

These numbers for wind and solar are worryingly low. Mankind has a so-called hierarchy of energy needs and desires, running from basic requirements like heat and cooking, through to more sophisticated requirements like education and ‘nice-to-haves’ like the arts (Figure 14). It is progressively higher returns on energy investments that allow us enjoy these progressively greater benefits of civilisation. Every £1 of coal generates £10 of electricity, and every £1 of natural gas generates £15 of electricity. With these factors one can see how the modern world can run with an energy sector that is only 9% of the world economy. The question remains – are renewable energies productive enough to maintain a modern global economy as we know it? If we need to have a rather larger energy sector as a fraction of the global economy, we will be taking a reverse step in terms of the trajectory of Figure 3.

The challenge of megacities

In 2050 over half the world’s population will be living in megacities with populations of more than 5 million people. The energising of such cities at present is achieved with fossil and nuclear fuels, as can the cities of the future. The impact of renewable energies will be very small, as the vast areas of land needed, often taken away from local areas devoted to food production as in London or Beijing, will limit their contribution. The extreme examples are Hong Kong and Singapore, neither of which have any available hinterland. Recent progress on the vertical farming of leaf vegetables and the development of meat grown in laboratories means that megacities could be self-sufficient in both these contributions to the human diet from factories within the limits of these megacities. Only grain still needs the large areas of agriculture.

In the UK, 45% of carbon dioxide emissions come from heating air and water in buildings (27% in the domestic sector, and 18% in all others). In 2010, as chief scientific advisor to the then Department of Communities and Local Government, I convinced Lord Drayson, the Science Minister, to fund a pilot programme in which over 100 social houses would be retrofitted with external and internal cladding, double glazing and new appliances.∗ We targeted a reduction of 80% in emissions. However, of 45 specific projects where full before-and-after data is available, the average spend of £85,000 achieved an average emissions reduction of only 60%, with only three projects meeting the 80% target and some not even reaching 30%. Social houses are smaller than the average, and there are fewer detached houses, so it is clear that an average spend of as much as £150,000 may be required to achieve the 80% target. While in a national roll-out there may be some cost reduction from learning by doing, nearly every house will need a bespoke solution, as poor or imperfect insulation is worse than no insulation. The cost to the country will be of order £2-3 trillion and will require a workforce on the same scale as the NHS to deliver a total retrofit over 30 years. No one has discussed the opportunity costs of such a major commitment.


Before drawing my conclusions, I want to make a few miscellaneous points.

A history of gloom

There is a history of gloomy predictions about mankind that coincides with the industrial revolution.

  • In 1798 Thomas Malthus FRS said: ‘The power of population is so superior to the power in the earth to produce subsistence for man, that premature death must in some shape or other visit the human race.’
  • In 1868, William Stanley Jevons FRS wrote The CoalQuestion, the key message of which was to halt the industrial revolution since the collapse of society upon the exhaustion of coal reserves was too terrible to contemplate.
  • In 1970, Paul Ehrlich ForMemRS suggested that European civilization would collapse before 2000 because of overpopulation and mass starvation.

The irony of all these examples is that the solution to the problem was at hand at the very time the Jeremiahs spoke. The combine harvester trebled the efficiency of the harvest and – apart from the potato famine (a political famine) – no one starved in Europe. The discovery of oil and gas greatly expanded the availability and expected duration of fossil fuels. The green revolution of Norman Borlaug ForMemRS introduced new strains of wheat, and hunger now appears to be in terminal decline. In contrast to all this, in 1830 the 1st Baron Macaulay FRS asked:

On what principle is it that, when we look we see nothing but improvement behind us, we are to expect nothing but deterioration before us? I have some sympathy with this point of view.

Future demographics

I suggest that the demographic transition that started 70 years ago is the solution to those who cry wolf about the climate now. In the countryside, another child is a useful pair of hands from the age of 6, while a child in a city is a burden until they are 15. Everywhere in the world where more people live in cities than the countryside (North America, Europe, Japan and Australasia), the local population (excluding immigration) is in decline, with fewer than 2.1 children per family. Globally, the number of children per family has halved since 1970 from 5 per family to 2.3 today. China’s population will peak in the early 2030s and will be less in 2060 than it was in 2000.† There will be 200 million fewer people on earth in 2100 than at the peak in the 2060s.‡ There will be plenty of empty houses for people who are actually displaced by any sea level rise at that time.

The climate change imperative

In the 1990s the global average surface temperature had been rising sharply for 15 years, and many predicted that this rate of warming would continue, when in fact it has halved. This lesson of history is regularly ignored as the current level of climate alarm is cranked up.

The upsides of more carbon dioxide in the atmosphere.

The historical character of science was a dispassionate evaluation of all the relevant facts on a particular issue. It is sad that the upsides of increased carbon dioxide levels in the atmosphere (such as the greening of the biosphere) are systemically ignored or discounted, while those matters which are neutral, such as storm frequency and severity are spun to be hostile to humanity. All the data shows that extreme events were more extreme and more common in the first half of the 20th century, but climate change is supposed to have started in 1960 – in most accounts.


The smart phone is an epitome of dematerialisation of the world economy. The services now fitting in the palm of the hand would thirty years ago have required a table full of equipment – phone, TV, video recorder and player, alarm clock, dictaphone, newspapers and magazines, TV, answerphone, letters.

Sense of balance

For £1 devoted to mitigating climate change, how much money should be set aside for mitigating Carrington events, pandemics, global financial collapse, volcanoes, earthquakes and tsunamis, and other threats? What is the appropriate level of global insurance, and indeed the insurance for poorer countries?

Mitigating climate change as a civil engineering project

If I were able to raise £1 trillion a year for ten years, and devote it to mitigating climate change, there is no answer to date to the simple questions that are the starting point of any engineering project. What are the specific projects that should best be funded and to what level? How do we measure the consequential reductions in climate change so that we can assess the value for money after the event, if not before? No-one has any clue how to assess value for money in advance.</> <>Conclusions</> <>It is clear to me that, for the sake of the whole of mankind, we must stay with business as usual, which has always had a focus on the efficient use of energy and materials. Climate change mitigation projects are inappropriate while large-scale increases in energy demand continue. If renewables prove insufficiently productive, research should be diverted to focus on genuinely new technologies. It is notable that within a few decades of Watt’s steam engine becoming available, the windmills of Europe ceased turning. We should not be reversing that process if the relative efficiencies have not changed.

We must de-risk major infrastructure projects, such as mass decarbonisation. They are too serious to get wrong. Human lifestyle changes can have a greater and quicker impact: they could deliver a 10% drop in our energy consumption from tomorrow. This approach would not be without consequences, however. For example, airlines might well collapse if holidaymakers stayed, or were made to stay, at home. Who owns the integrity of engineering in the climate debate in the United Kingdom? Globally? The Royal Society, the Royal Academy of Engineering and the Engineering Institutions should all be holding the fort for engineering integrity, and not letting the engineering myths of a Swedish teenager go unchallenged.


I wish to thank Marjan Waldorp of for pointing out an error in my original text regarding energy density for lead-acid batteries. I want to thank the many colleagues that have helped me over the last decade, and continue to help me now. Thanks to Andrew Montford for editing and presenting this text.

Further reading

M J Kelly, ‘Energy efficiency, resilience to future climates and long-term sustainability: the role of the built environment’, Philosophical Transactions of the Royal Society A 2010; 368 1083–89.

M J Kelly, ‘Why a collapse of global civilization will be avoided: a comment on Ehrlich and Ehrlich’, Philosophical Transactions of the Royal Society B 2013; 280: 20131193.

M J Kelly, ‘Technology introductions in the context of decarbonisation: Lessons from recent history’, The Global Warming Policy Foundation, GWPF Note 7, 2014, http://www.thegwpf. org/content/uploads/2014/03/Kelly-lessons.pdf.

M J Kelly, ‘Future energy needs and engineering reality’, Journal of Energy Challenges and Mechanics 2014; 1(3): 1.

M J Kelly, ‘Lessons from technology development for energy and sustainability’, MRS Energy & Sustainability 2016; 3: 1-113.

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