Sustainable development means improving the quality of life within the capacity of supporting ecosystems (I.U.C.N. et al., 1991), but what are the limits to this capacity? Just how much can Nature take? The concepts of 'critical loads' and 'environmental space' are an attempt to define the limits.
It is important to stress that these limits are thresholds over which we should not stray, rather than a capacity for us to use up. Generally, however, we are well above the thresholds and drastic reductions in our use of resources and our output of wastes and pollutants are necessary.
Critical loads represent, for each pollutant, the maximum input to an ecosystem, which will not damage its structure and function in the short or long term. Because of the transboundary nature of air and water pollution, critical loads have to be set according to the most sensitive ecosystems.
The Third International Non-Governmental Organisation Strategy Seminar on Air Pollution in 1992 set objectives for immediate reduction in European emissions of air pollutants as follows.
| Pollutant | Minimum reduction in emissions |
| Sulphur dioxide (SO2) | 90% |
| Nitrogen oxides (NOx) | 90% |
| Volatile organic compounds (V.O.C.) | 75% |
| Ammonia (NH3) | 75% |
| Tropospheric ozone (O3) | 75% reduction in concentrations, to be achieved by meeting the above objectives for NOx and V.O.C.s. |
The above minimum reductions are from the emission levels of the early 1980s and apply to the whole of the continent of Europe, including the European part of Russia. Whilst being minimum demands, greater reductions are necessary from countries with very high emissions (including the U.K.), whilst the necessary reductions could be lower in some other areas.
As regards the U.K., sulphur emissions dropped by about 20% between 1980 and 1990, whilst NOx emissions increased by about 12%. The actual amounts are shown below, together with the minimum necessary cuts to meet the European average minimum objectives above.
| U.K. Emissions of Sulphur and Nitrogen Oxides | ||||
| 1980 | 1990 | Reduction necessary to (from 1990 emission levels) | ||
| Sulphur (1000 tonnes) | 2424 | 1916 | 243 | (87%) |
| NOx (1000 tonnes as NO2) | 2278 | 2573 | 228 | (91%) |
For much resource use and for certain pollutants, the impact is not just European, but global. It is for instance now clear that there will be some significant impact on climate globally by the middle of the 21st century even if all human emissions of 'Greenhouse' gases (carbon dioxide, hydrocarbons, chlorofluorocarbons) were to cease today. Furthermore, there is the question of global equity; we in the so-called developed countries will have to cut our consumption and emissions more than calculations based on today's situation would imply, in order to allow people in the so-called developing countries to improve their quality of life, which is likely to result in increased consumption and emissions, at any rate in the short term.
The concept of environmental space takes on board global equity and apportions fairly the total capacity of the environment to provide the physical and non-physical resources we humans need. Environmental space therefore represents the total amount of resources (such as energy, raw materials, waste absorption, genetic diversity, climate regulation, etc.) available to us at any given time, which does not damage supporting natural systems and thus does not prevent future human generations making use of the same amount. Research at the Institute for Climate, Energy and Environment in Wuppertal (Germany) suggests that our consumption of environmental resources in so-called developed countries will have to be cut by up to 80-90%. On this basis, the following example reductions are needed across Europe (here excluding the former Soviet countries).
| Example targets for per capita reductions in environmental resource use by 2050 (ideally sooner) for Europe | |||
| Resource | Current (1990) 'consumption' | Sustainable 'consumption' | Per cent reduction |
| Primary energy | 123 GJ | 60 GJ | 50 |
| Fossil fuels | 100 GJ | 25 GJ | 75 |
| Carbon dioxide emissions | 7.3 t | 1.7 t | 77 |
Applying the above minimum objectives to London, the reductions shown at the bottom of the following table result. The figures in the table (extracted from Chell & Hutchinson, 1993) apply basically to the area of Greater London and thus exclude pollutants due to London but emitted outside its boundaries, for instance in production of goods consumed in London or in transporting these and commuters to the city. The figure for reduction in carbon monoxide (CO) emissions is on the basis of CO being oxidised in the atmosphere to carbon dioxide (CO2); reductions required for health reasons are thus likely to be different. The V.O.C. figures exclude both methane and emissions from sources other than energy-related uses, which constitute 50% of the total.
| Sources of Principal Air Pollutants for the London Area in 1991 (%) | |||||
| Sector | CO2 (as C) | CO (as C) | SO2 | NOx | V.O.C. |
| Road transport | 33 | 99 | 22 | 76 | 97 |
| Other transport | 3 | 1 | 1 | 4 | 1 |
| Industry | 15 | 0 | 43 | 6 | 1 |
| Domestic | 30 | 0 | 1 | 6 | 1 |
| Other | 19 | 0 | 32 | 8 | 0 |
| Total (thousand tonnes) | 8508 | 648 | 26 | 137 | 116 |
| Necessary reduction (%) | 77 | 77 | 87 | 91 | 75 |
| Nett emissions (thousand t) | 1957 | 149 | 3 | 12 | 29 |
The same report quotes energy consumption in London as 89.1 GJ per capita in 1991, divided up as 46% gas, 37% petroleum, 16% electricity and 1% solid fuel. However, this is specific energy, rather than primary energy (the energy in the fuel prior to processing for use). It is therefore fair to assume necessary the 50% reduction in primary energy use stipulated in the environmental space work.
These reductions do not necessarily imply that the activities that produce the emissions have to be reduced in proportion (although in some cases this may be true). There are two basic ways forward, both assuming the delinking of the consumption or use of goods and resources from resource depletion and environmental impact:
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The information summarised in this paper has been gleaned from the following sources. Thanks to Paul de Zylva of Friends of the Earth London for some of this material.