The successor to “Factor Four” (first published in 1997) has been published by Earthscan in December.

Factor Five
Transforming the Global Economy through 80% Improvements in Resource Productivity
By Ernst von Weizsäcker, Karlson ‘Charlie’ Hargroves, Michael H. Smith, Cheryl Desha and Peter Stasinopoulos

Picking up where Factor Four left off, this new book examines the past 15 years of innovation in industry, technical innovation and policy. It shows how and where factor four gains have been made and how we can achieve greater factor five or 80%+ improvements in resource and energy productivity and how to roll them out on a global scale to retool our economic system, massively boost wealth for billions of people around the world and help solve the climate change crises.

Spanning dozens of countries including China and India and examining innumerable cases of innovation in design, technology and policy, the authors leave no engineering and economic stone unturned in their quest for excellence. The book tackles sustainable development and climate change by providing in depth Factor 5 resource productivity studies of the following sectors: Buildings, Industry, Agriculture, Food and Hospitality, and Transportation.

In its systematic approach to demonstrating how Factor 5 can be achieved, the book also provides an overview of energy/water nexus and energy/materials nexus efficiency opportunities across these sectors. Given that these sectors are responsible for virtually all energy usage and greenhouse gas emissions globally, this book is designed to guide everyone from individual households, businesses, industry sector groups to national governments in their efforts to achieve the IPCC recommended target of 80 per cent reductions to greenhouse gas emissions.

It also looks at innovation in regulation to increase resource productivity, pricing, carbon trading, eco-taxation and permits and the role of international institutions and trade. The authors also explain exciting new concepts such as bio-mimicry and whole system design, as hallmarks for a new generation of technologies. The last part of the book explores transformative ideas such as a long term trajectory of gently rising energy and resource prices, and new concepts of well-being in a more equitable world.

The book can be ordered online from Routledge here: http://www.routledge.com/books/details/9781844075911/

To receive a 20% discount when ordering online at routledge.com, please enter the voucher code AF20.

The German edition, titled “Faktor Fünf”, will be published by Droemer Knaur in March 2010 and can be pre-ordered online: http://www.droemer-knaur.de/buecher/Faktor+F%C3%BCnf.891358.html

Dear Professor Lu Mai, dear Professor Liu Shinjin, ladies and gentlemen,

It is an unusual honour for me to be invited to this keynote address, which I have put it under the title of Resource Productivity.

Fig 1

This title contrasts with the preoccupation with labour productivity during the last 200 years of technological progress. Labour productivity has been the melody of the first Industrial Revolution. It increased twentyfold or more during those 200 years. This has been the basis of prosperity and it is the main theme of China’s stunning economic progress.

During those same 200 years, the world has also seen a systematic decrease of prices of natural resources.

Fig 2

This invited mankind to a wasteful use of those resources. Small wonder, then, that resource productivity was stagnant or even decreasing during much of this time.

Let me submit to you that we cannot continue on this road. It may be wise, chiefly for the industrialized countries to slow down the further increase of labour productivity while forcing the increase of resource productivity.

Forcing resource productivity has become an imperative also for the developing countries that cannot afford a wasteful use scarce resources. Obviously, this consideration was at the roots of planning this conference. The new trend in technological development, namely a strong emphasis on resource productivity, may be triggered by the recent increase of resource prices:

Fig 3

For China in particular, the rising commodity prices were a signal of warning. But then, you have additional reasons to become more resource efficient. It would allow you to simultaneously reduce one major health problem, namely pollution-caused mortality in your industrial agglomerations:

Fig 4

Clearly, air pollution should also be addressed directly by appropriate pollution control measures. These have an additional cost, which however, is far exceeded by the economic benefits for China, according to Stefan Hirschberg et al (2003) of the Swiss Paul Scherrer Institute:

Fig 5

China is going through the standard development with regard to pollution: Countries start poor and clean. Then they industrialize and get rich and dirty. And then they rich enough so that they can afford pollution control and end up rich and clean:

Fig 6

It has been the traditional view of the developing countries that they are too poor to pay for pollution control. As Indira Gandhi said it in 1972 at the first UN Conference on the Human Environment in Stockholm: “Poverty is the biggest polluter”

Fig 7

Indira Gandhi’s slogan went down well not only with the political leaders of developing countries to whom it was a nice excuse for not acting on pollution control, but also for industry in the North that could conveniently say that they needed good profits for the sake of the environment.

The trouble is that today’s biggest environmental problems, biodiversity losses and climate change, are chiefly caused by the rich.

Fig 8

Regarding biodiversity, the biggest problem is habitat losses due to increased land use for agriculture, settlements, mining, energy and transport. You can estimate the acreage that is needed per person for a sustainable supply of all the daily goods and services. This is then the “ecological footprint” according to William Rees and Mathis Wackernagel, caricatured in the next picture:

Fig 9

The ecological footprints of average Chinese people are roughly one hectare. We in Western Europe have footprints four times as large, and in the US and Canada, footprints are even eight times that size. If all 6.3 billion people had US type lifestyles, we would need three to four planets Earth to accommodate all their footprints. This is obviously unsustainable.

The other big problem is global warming. Global temperatures have been rising and falling over the last 160.000 years in close correspondence with CO2 concentrations.

Fig 10
Based on the physics behind this correlation, the Intergovernmental Panel on Climate Change (IPCC) has projected temperatures to rise dramatically during our century:

Fig 11

The consequences could be alarming for water, food security and for biodiversity. You would also have to count with more devastating typhoons and, most dangerous perhaps, with a rising sea water table, indicated by the green line in the next picture.

Fig 12

The difference between high and low water tables is more than 100 metres, which means that coast lines will heavily vary. The next picture shows it for Italy. 20.000 years ago, during the last Ice Age, the Sea was lower and Italy was larger than today. But two million years ago there were no polar ice caps (and also the geological situation was different in the Mediterranean Basin) so that Italy was much smaller:

Fig 13

At present, we see a dramatic change of temperatures in the Arctic region, as has been discussed in the Arctic Climate Impact Assessment (2004). The summer freshwater coverage of Greenland has increased more than fourfold in ten years:

Fig 14

We are unable to predict the consequences of this development. But we know from historical records that ice masses can collapse or glide into the oceans in a very short period of time. This has been the case with the ice shield once covering Labrador and the Hudson Bay, which disintegrated during a few decades, perhaps even a few weeks some 7800 years ago, letting the sea water table rise by some 7 metres:

Fig 15

Imagine what such a mega-event would mean for China’s or Japan’s coastal areas, or for the Netherlands or Egypt or Florida!

What do we have to do to prevent such disasters from happening? It is plausible that at least we should try to stabilize CO2 concentrations. This, however, will require us to reduce annual CO2-emissions by 60-80 percent, according to the IPCC. Let us optimistically assume that 50 percent will do. But under the present trends, we shall get exactly the opposite. We are heading for a doubling of CO2-emissions:

Fig 16

China, India and other countries are drastically expanding their industrial outputs, their motorized transportation and their energy consuming housing and agriculture. So we shall see China and India to have emissions similar to those of the US:

Fig 17

Fig 18

The world energy pie shows that worldwide we have still an overwhelming dominance of fossil fuels.

Fig 19

In Europe, we have begun systematically to work on the reduction of CO2-emissions. The trading began in December, 2004. Initially, the prices paid per ton of CO2-emissions were at around 8 Euros. Meanwhile, prices have roughly doubled.

Fig 20

One component of our combating greenhouse gas emissions has been the increase of renewable sources of energy. In Germany, we have been quite successful in this:

Fig 21

We were very glad to see a large Chinese delegation at the Renewables 2004 conference in Bonn last year, and many said that China was about to copy the German system and is now planning another such conference this November. However, for all their merits, the renewables will not suffice to solve the problem. The energy pie is simply too large and must be reduced if we want to fight global warming and also avoid a dangerous dependence on nuclear power.

The key to the answer will be a Second Industrial Revolution focussing on the strategic increase of resource productivity. This has been the vision in the book “Factor Four. Doubling Wealth, Halving Resource Use”, which was also translated into Chinese:

Fig 22

It has been known for a long time that lower energy intensity is a sign of modernity:

Fig 23

We therefore see the Factor Four story as a true continuation of technological modernization and progress.

Let me now open a window for you to look into the new universe of eco-efficient technologies. The pictures will mostly compare existing technologies on the left hand side with new technologies on the right hand side that are some four times, or even ten or a hundred times more resource efficient than the old ones.

Fig 24

Let me start with my co-author’s Amory Lovins’ favourite idea, the “hypercar”, which allegedly does 150 miles a gallon, or needs only 1,5 litres per 100 kilometres.

Fig 25

Some remain a bit sceptical about its success but according to Amory, some 2 billion dollars have already been invested in the concept.

Fig 26

The next is Amory Lovins’ institute and home, the Rocky Mountain Institute, high up in the Rocky Mountains, which during much of the year is largely energy-self-sufficient and is easily a factor of ten better regarding energy than typical mountain.

Fig 27

The concept has been transferred ten years ago to ordinary apartment houses in Germany and elsewhere, as “passive houses” making use of solar heat and of heat exchange ventilation.

Fig 28

In my political constituency, Stuttgart, or rather in nearby Fellbach, we have a true zero-external-energy house. It has become a tourist attraction. And part of the excess energy it produces is channelled into a super-efficient car.

You all know the efficient light bulbs that need only a quarter of the electricity used in old incandescent bulbs. China has become the largest manufacturer worldwide of the efficiency bulbs. However, as most of you know, this is not yet the end of the road. Light diodes are coming up that are yet another factor of two or three better than the efficiency bulbs shown on the picture.

Fig 29

This is a small cooling chamber to replace the refrigerator that stands freely in the kitchen. Two weeks ago, I met with a Japanese gentleman who told me that even freely standing refrigerators have now been developed that are seven times more energy efficient that the old ones. The new development was probably triggered by the “Top runner programme” of Japan.

Fig 30

Fig 31

If you replace the old-fashioned filing cabinet technology by CD ROM’s you save more than a factor of ten and you have easier access to your data.

Fig 32

Water scarcity is one of the biggest problems of China. You may therefore be interested in a technology used in Germany that has reduced water consumption twelve fold in paper manufacturing, chiefly by systematically recycling and cleaning waste water.

Fig 33

My friend Professor Ryoichi Yamamoto of Tokyo once sent me the above picture showing a thin rod of steel that has the strength and capacities of otherwise ten times more resource consuming steel.

Fig 34

Video conferences are, of course, something like a factor of one hundred more energy efficient than the otherwise necessary business travel. I admit that video does not easily substitute for a business meeting on the Bahamas.

Fig 35

This is the story of modern, energy intensive agriculture. Winter tomato grown in greenhouses in Holland tend to need a hundred times more energy than they afterwards contain! With intensive cattle farming, the ratio is hardly better. Organic farming, on the other hand, is roughly by a factor of four more energy efficient.

Fig 36

This is the well-known strawberry yoghurt saga established by Stephanie Böge at the Wuppertal Institute. Lorries criss-cross Europe and drive some 8000 kilometres for the manufacturing of strawberry yoghurt. Obviously you could do at least ten times better.

So much perhaps to encourage you to think further about the upcoming technological revolution. Let me close by making a few remarks about methods to arrive there.

China is one of the countries that has established efficiency standards for cars. To meet the 2008 standards, many European and American car manufacturers have still to do considerable homework, while Toyota is well prepared.

Fig 37 [*]

In the business world we seem to see a slight competitive advantage of eco-efficient companies listed in the Dow Jones Sustainability Index over the average listed in the Dow Jones Group Index.

Fig 38

And if you compare different countries using the World Economic Forum’s Competitiveness Index you see a positive correlation with the Sustainable Development Index of countries.

Fig 39

So we seem to be on a good way. However, this is all too slow to reach the necessary factor of four. Let me in closing say a few words about instruments. I am impressed with what I heard in China about the determination with which you are creating incentives for more resource efficient technologies. Moreover, Douglas Ogden this morning mentioned the possibility of tax refunds for companies that achieve ambitious standards, and James Sweeney spoke about appropriate pricing.

Japan has gone a considerable step further with her “top runner programme” that makes the most energy efficient appliance or vehicle the top runner or standard and announces shame on those companies in a few years that still sell outdated, less efficient items. Ultimately they even have to pay a fine.

Germany and other countries have adopted an ecological tax reform to reduce the fiscal load on human labour while making natural resources more expensive.

And at the G 8 Summit that takes place in a few days, we hope countries agree on a geographical extension of climate policy beyond “Kyoto”. We hope that also China, India, Brazil etc will be invited under fair term to join international climate policy.

For this, the North has to understand that the present “grandfathering” approach is unfair to the developing countries and has to be replaced step by step by a system based on per capita allowances, – which would be good for China and India.

Mr. Chairman, ladies and gentlemen, I feel that the race is on worldwide among countries and among companies to take the lead in the Second Industrial Revolution that is driven by the second melody of progress, the melody of a revolutionary increase of resource productivity.

Thank you for your patience and attention!

References

• Hirschberg, Stefan, et al. 2003
• Rees, William and Mathis Wackernagel
• Von Weizsäcker, Ernst Ulrich, Amory Lovins and Hunter Lovins. 1997. Factor Four. Doubling Wealth, Halving Resource Use. A Report to the Club of Rome. London: Earthscan. Also available in Chinese and ten other languages.

[*] After the lecture, I was approached by a reresentative of General Motors who said that GM had also met the standards with cars exported to China.

Why Sustainable Development?

We live in a finite world. Ultimately, there is no way around production and consumption patterns that are sustainable. Ultimately, customers, engineers, managers and politicians will show a strict priority for the respect of nature and the environment.

To be sure, global competition for highest cost-benefit ratios leaves little breathing space for such long-term considerations. But at any moment in time it is legitimate to ask oneself if the time has come to now make sustainable production methods and ecologically benign products the priority for the company.

Many people in the business community believe that most of the environmental homework has been done leaving not much to do. This optimistic conviction is based on the inverted U-curve”. Countries typically start poor and clean. Then they industrialise and become rich and dirty. Once they are rich enough to afford costly pollution control, they finally become rich and clean.

Fig. 1: Countries historically started poor and clean, then got industrialised and dirty and ended up rich and clean.

The trouble is that ”rich and clean” involves per capita consumption levels of depletable resources easily twenty times the rate of the ”poor and clean” stage. In the language of William Rees and Matthis Wackernagel (1992), lifestyles in the rich and clean countries involve ”ecological footprints” of some four hectares per person. Similarly, Friedrich Schmidt-Bleek has developed the concept of ”ecological rucksacks”. Every average Japanese causes an ecological rucksack every year of some 45 tons. Germans cause even heavier rucksacks weighing some 60 tons. Heaviest, of course, are the US American rucksacks of some 80 tons annually.

All in all, we are far from a harmonious situation. In fact the daily toll of environmental damages can be seen as absolutely alarming, as Fig. 2 is summarising.

Fig. 2: The alarming daily toll of environmental destruction.

Among the most alarming effects of our footprints and of the rucksacks is the rapid loss of biodiversity. At present, we are losing some twenty, perhaps up to one hundred plant and animal species every day. This is mostly due to the destruction of natural habitats that have been the home to hundreds of thousands of biological species, some of them rather inconspicuous but nevertheless important in the interlocking webs of ecosystems. Habitat destruction mostly results from land conversion for mining, agricultural use, forest monoculture, or settlements. Even if much of the land degradation is taking place in the developing countries, it is often exports of timber, ores, fodder and fruits to the North that cause the degradation. In other words, we in the rich countries tend to export our ecological footprints to the South

One of the most disquieting aspects of environmental change is the greenhouse effect. The Intergovernmental Panel on Climate Change (IPCC) has published fears of global warming by up to 5 degrees during this century. (Fig. 3).

Fig 3: Projections of global warming until 2100 (Source: IPCC, 2001).

Global warming can be accompanied by a further rise of the sea levels. Fig. 4 shows how the coast lines of Italy reacted to different levels of the sea water table.

Fig. 4: Italy during the last Ice Age and during the Pliocene.

There is still a lot of ice on the Antarctic and on Greenland, enough to flood Holland, Bangladesh, Egypt, Florida and much of Germany.

We should by all means avoid such disasters. The IPCC has suggested that in order to stabilise carbon dioxide concentrations we should reduce carbon dioxide emissions by some 60 to 80 percent, say by 2050. On the other hand, we learn from the World Energy Council, that the demand for energy, and with it the emissions of carbon dioxide, are likely to rise steeply and are most likely to at least double within that period. So there is a gap as large as a factor of four which will have to be closed.

Nuclear energy can’t close the gap. Today, nuclear energy is a mere six percent of the world energy pie, and in most countries, even the most ardent defenders of nuclear energy have stopped ordering any new reactors. Even a neck-breaking rush towards tripling nuclear energy supplies in the world would not buy more than is an increase from six to eighteen percent of the energy pie. And if that pie is doubling, we are falling back to a mere nine percent.

The substitution of fossil fuels by renewables is a lot nicer to the environment. But then wind and solar make up only 0.5% of the present pie. Let us assume a heroic strategy of increasing it twenty fold. Then we have reached ten percent of the present pie, but a mere five percent of the double sized pie.

Let me conclude this introductory section by stating plainly that energy policies too are in a massive dilemma.

After the Industrial Revolution the Eco-Efficiency Revolution

The challenges of sustainability, of biodiversity protection and of climatic change look breathtaking. Fortunately, there is hope. Much of this hope is rooted in technological progress. But the task will be no smaller than the adventure of the Industrial Revolution. Having listened to some of the participants of this conference in advance, I am confident that the radiation curing industry can play a significant part in our new adventure of technological progress. However, I don’t claim the competence for giving you any special technological advice. Let me instead try and characterise the broader features of that new technological revolution.

In the early days of the Industrial Revolution, technology was mostly driven by the desire of economic expansion. The main emphasis was laid on the increase of labour productivity, which may have risen twenty fold during the last 150 years. This progress becomes visible in the speed of our vehicles, in the power of our machines, in the organisational miracles of industrial production lines and in the unprecedented skills of modern information technologies.

The emphasis on labour productivity was very reasonable until quite recently when human labour was indeed very inefficient and very hard too. The resources of nature seemed to be nearly unlimited. So the exploitation of nature seemed like a legitimate and natural part of the game for much of technological history.

Today we are living in a completely different world from the early 19th century. Labour today is abundant, labour productivity is very high, and the real scarce resource is nature. This means it is high time now to concentrate our efforts on the increase of resource productivity. Even purely economic — and social — reasons speak for it. Slowing down the increase of labour productivity while speeding up resource productivity should make countries richer, not poorer.

Shifting emphasis to resource productivity should be the best answer also to the challenge of sustainable development. The World Business Council for Sustainable Development now speaks of Eco-Efficiency as a new guiding term. And the Wuppertal Institute of which I have been the founding president, gives ambitious goals for the increase of resource productivity. For the use of materials, my friend Friedrich Schmidt-Bleek calls for a decupling of resource productivity. But for energy, I suggest a more modest figure of a factor of four. At any rate, we are speaking of productivity jumps equally impressive as those characteristic of the Industrial Revolution. Let us therefore speak of the Eco-Efficiency Revolution, which we shall be forced to launch very soon.

The Eco-Efficiency Revolution is perhaps the only strategy allowing a reduction in size of the ecological footprints without jeopardising employment and competitiveness.

Factor Four

The good news is that quadrupling resource productivity is technologically feasible. A 1995 Report to the Club of Rome (in English: Weizsäcker, Lovins and Lovins, 1997) features fifty examples for the potential of increasing resource productivity by a factor of four at least. Twenty examples were selected in the field of energy, twenty in material resource productivity, and ten in transportation.

Fig. 5: Factor Four was translated into twelve languages including Chinese and Japanese.

My co-author Amory Lovins lives in and works at the “Rocky Mountain Institute”, some 2000 metres above sea level in a truly cold climate. And yet his home needs almost no external energy. It is easily a factor of four more energy efficient than ordinary alpine buildings. The next picture compares the two in terms of energy productivity.

Fig. 6: The Rocky Mountain Institute is perhaps ten times more energy efficient than an ordinary alpine house.

Another very attractive Factor Four example is what my co-author Amory Lovins has dubbed the hypercar {Fig 7}. By almost entirely redesigning cars, making them light-weight and still crash-resistant, and by using modern hybrid engines, the average fuel efficiency can be pushed up to 150 miles per gallon, which is more than four times better than today’s fleets.

Fig. 7: Amory Lovins’ “Hypercar” (right) is five times as fuel efficient as ordinary cars (left).

Other examples include light bulbs, refrigerators, air conditioners, TV sets, mechanical fans, pumps and motors, computers and other office equipment.

Also renewable sources of energy will play an important role in the efficiency revolution. They may not by themselves save energy but they are at least ”carbon-efficient” and lend themselves to being combined with efficiency technologies, e.g. the use of passive solar energy in buildings can be optimised by the so-called translucent insulation technique.

A different and very important sector of energy use is nutrition. By reducing the excessive use of fertilisers and the transportation of fodder, and by slightly cutting meat consumption, energy requirements for a healthy diet can be cut by a factor of four.

The twenty examples of revolutionising material productivity range from construction and durable office furniture, to water in homes, in paper manufacturing and to high tech recyclable plastics for wrapping and catering. One fine example is the replacement of a clumsy paper-based filing cabinet by a modern CD ROM system. There you save more than a factor of ten even if you generously include the ”ecological rucksacks” of the metal contained in the disks. One example is modern steel, which can be easily four times as resource efficient per unit of results obtained (Fig. 8)

Fig. 8: Modern steel can be fabulously strong and can help saving 75% materials.

Let me present one last example from our book, the logistics of the production of strawberry yoghurt. Stefanie Böge has found out that for manufacturing a cup of strawberry yoghurt in Germany you would typically let lorries criss-cross central Europe and make 8000 kilometres, if suppliers and the suppliers of the suppliers are counted. It can easily be proven that you can do an equivalent job with only a thousand kilometres, which again is more than a factor of four. (Fig. 9)

Fig. 9: The distance of total lorry traffic for the manufacture of strawberry yoghurt today (left) and in an energy efficient future (right).

I may have opened a window for you into a distant future of technologies and everyday habits of people, There will be millions of small transformations, some of them quite inconspicuous, that make up the factor four revolution. I am perfectly confident that the revolution will be as benign as the industrial revolution, although surely there will be losers, chiefly among those who do not want or cannot keep pace. That, however, is not exactly new in the history of industry.

Profitability, long term and short term

Needless to say much of the efficiency revolution is not going to happen unless the framework for doing business is changed. Efficiency must be made profitable. Fortunately, some eco-efficiency is profitable now. (Fig. 10).

Fig. 10: A portfolio of stocks of ecological “best in class” companies had a better performance than the DJGI

A portfolio of stocks of ecological “best in class” companies had a better performance than the Dow Jones Group Index. Companies paying attention to the resource and energy flows going through the firm, tend to gain internal transparency and to enjoy better staff motivation and better customer relations. This is perhaps the most convincing explanation for their encouraging stock exchange performance.

It is to be feared, however, that the potential for making profits by eco-efficiency measures will be very limited if the present world market conditions prevail. Energy and natural resources are still too cheap because markets are rather blind with regard to long term scarcities and to such developments as the greenhouse effect.

Moreover, conventional policies in most countries have even subsidised the use of natural resources. André de Moor (de Moor and Calamai, 1997) has estimated that some 700 billion dollars are spent annually in subventions given to the four fields of energy consumption, water, agriculture and motor transport. This does not even account for all the tax advantages, free infrastructure and land given to investors. De-subsidising resource use will be an important part of ecological policy worldwide.

Another and related policy tool is ecological tax reform. In a world of growing unemployment and of scarce natural resources it just doesn’t make sense to draw the biggest part of fiscal revenues from human labour while resource use is essentially free of charges. The German government has made some first steps in that direction, as have many other European countries. Perhaps certain details were not well designed so that the programme is not exactly popular.

The EU is now introducing an international trade regime for permits of carbon dioxide emissions. Economists believe that this instrument can be more cost-effective than ecological tax reform.

This is just the beginning. I remain confident that future generations will find it easy to accept market interventions making scare resources dearer and abundant resources cheaper. That is pure economic rationality and should make countries richer, not poorer.

I hope that your innovative branch of industry with it’s fascinating advances in UV/EB and radiation curing will be part of the driving force for a more prosperous and more sustainable society world-wide!

References

• de Moor, André and Peter Calamai. 1997. Subsidising Unsustainable Develop­ment; Undermining the Earth With Public Funds. Toronto: Earth Council.
• Hawken, Paul, Amory Lovins, Hunter Lovins. 1999. Natural Capitalism. Creating the next industrial revolution. Boston: Little Brown
• Rees, William and Mathis Wackernagel. 1994. Ecological Footprints and Appropriated Carrying Capacity. In A.M. Jannson (Ed) Investing in Natural Capital. New York: Island Press.
• Schmidheiny, Stephan and the Business Council for Sustainable Development. 1992. Changing Course. Cambridge, MA: MIT Press.
• Schmidt-Bleek, Friedrich. 1994. Wieviel Umwelt braucht der Mensch? Basel: Birkhäuser.
• Weizsäcker, Ernst von, Amory Lovins and Hunter Lovins. 1997. Factor Four. Doubling Wealth, Halving Resource Use. London: Earthscan.