Prof. Geoff Hammond, University of Bath, on 25 October 2002

Prof. Hammond began by discussing global warming and pointing out that the evidence for (or against) it is not certain. However, he thought we should go for preventive measures whether or not the warming is occurring, since the side effects of those measures are worth having as they reduce the pollution in cities of CO2 and NOx. There are also regional benefits by reducing the levels of particulates in the air, and hence their cooling effect on the local climate. When the climate is modelled and compared against the actual data since 1860, it appears that there is a significant effect from aerosols like sulphates, although it is still too early to be definite about the validity of the models.
Looking at CO2, 95% of the emissions in the UK come from the energy sector, and the government aims to reduce these by 60% by 2050. Looking at the full fuel cycles the various ways in which energy is generated, coal used to be the most polluting, but more advanced methods now make coal about as polluting as oil. However, gas produces only about half the CO2 emissions as oil. Nuclear energy is not completely free of carbon pollution as the power stations need to be built, and that uses energy. The decline of manufacturing activity has had good side effects in reducing the energy used in the UK.

Jonathan Porritt (2000) distinguishes between sustainable development (the process or journey) and sustainability (the end state). The former has been defined by the Brundtland Report (1987) as "Meeting the needs of the present without compromising the ability of future generations to meet their own needs". To achieve sustainability, there are 4 conditions according to Karl-Henrick Robert:
1. Finite materials should not be extracted from the Earth's crust at a faster rate than they can be deposited.

2. Artificial materials (including plastics) should not be produced at a faster rate than they can be broken down by natural processes.
3. The biodiversity of ecosystems should be maintained, while renewable resources should be consumed at a slower rate than their replenishment.

4. Basic human needs must be met in an equitable and efficient manner.

It is recognised that these conditions probably cannot be fulfilled within the present economic constraints. The situation can be roughly modelled by the equation

Impact = Population x Affluence x Technology

or, to put clearer numbers on this:


Energy consumption = population x GDP per capita x energy use per unit of GDP


or, in terms of pollution:


Pollutant emissions =population x GDP per capita x emissions per unit of GDP


Some indications of the effects on each of the three terms that might be possible were given. For example, the population might be reduced by a factor of 2 in 50-100 years through family planning and changing the role of women in society. Affluence can be maintained by increasing the length of a products useful life, more recycling, and using fewer materials in design, and this may give a factor of 3-10 over 20 years. Technology can help by improving energy conversion and distribution efficiencies, using benign sources, and improving the design of products. This may give a factor 100-1000 over 50 years.

There are some key principles underlying sustainable development. For example, the precautionary principle, which has generated so much controversy. Engineers are not uncomfortable with it, but it tends to be used by opponents of a scheme to block any action at all. Its use should be founded on what is known and the real risks.

One of the most important measures is the `Environmental Footprint', which is roughly the area of the Earth's surface that is needed to support an activity. The pattern of consumption in Western lifestyles results in footprints much larger than the available land. In cities, the overshoot factors are for 20 for Bath, 125 for London, 16 for Santiago de Chile, and 200 for Vancouver. The average citizen of Bath requires 3.48 ha. of land to support him.

Looking at our use of energy, we see that the transport sector is the one that is rising most, but this is most difficult politically to do anything about. The UK will start to import oil again in the not too distant future. Globally, the supply of oil is largely from the Middle East and has a further life estimated at 20-40 years. Natural gas is supplied by Russia and the adjoining states and has a 40-70 year life. Coal is widely distributed and may last up to 240 years. However, it is important that best practice in the use of these fuels is passed onto the third world where 80% of the population live. The effects of China burning its coal with old technology could be dire.

In the longer term, we must aim to reduce our use of energy and replace what we must use by renewable resources. One possible substitute for oil in transport is dimethyl ether (DME), which can be made from biomass. Electricity can be generated from primary sources such as hydroelectric schemes, wind, tide and nuclear, but requires some form of storage to meet peak demands. Hydrogen is not as promising as one might think as there will typically be a significant amount of carbon to be disposed of in the manufacture of the hydrogen.


In the ensuing discussion, it was pointed out that there have been lots of attempts to improve energy technology without clear success. In fact, nuclear energy has a problem in that nowhere is it economic to use it for energy generation in a free market system, but if we do not think about it before we need it, it cannot be brought into use quickly when we will need it.

One of the questioners thought that freeing world trade encouraged nations to service others rather than use what resources they themselves had. This increased energy use in transport, and allowed possibly useful areas of the globe to fall into disuse.

Prof. Hammond ended by remarking that he has in mind a project to see how much heat and power could be obtained from the hot springs in Bath, a true local use of a local resource.

Andy Pepperdine