The Oxford online dictionary defines pollution as the presence in or introduction into the environment of a substance which has harmful or poisonous effects. This sounds pretty straightforward, but it actually deserves a bit of unravelling.
For a start, ‘the environment’ is a widely-used term which comes laden with emotional baggage. We talk of a ‘pristine’ or ‘unspoiled’ environment and of the harm which may come to it, particularly via human action. The inference is that ‘the environment’ is something which exists separately from humanity and that our presence is an unwelcome disruption.
But we are not talking here of some prelapsarian Garden of Eden but simply, as the dictionary puts it, in the surroundings or conditions in which a person, animal or plant lives or operates (to which we should really add micro-organisms as well). The point is that much of the environment we as a species live in is shaped by us, most obviously in urban areas but also in the form of farmland, much of which would once have been forested, in temperate regions.
That environment, influenced also by factors such as latitude, distance from the sea, height above (or below) sea level, seasonality and climate patterns, is more or less favourable to different species, with humans as the only animals which have found ways to inhabit almost the complete range of latitude across all seasons. But what may be a harsh environment for most species may provide a perfect ecological niche for another.
And factors other than temperature or rainful may be harmful for some species and beneficial for others. Salinity, for example, is very bad for most plants, but some are adapted to growing by the sea and macro-algae (seaweed) thrives on it. But some things have few if any upsides, and particulate air pollution is one of these.
We read last week that High pollution hits southern England (doubtless this affected other countries as well, but we Brits can be quite parochial). The concern is over fine particulate matter, especially PM2.5 (below 2.5 microns in diameter). These can penetrate deep into the lungs and cause severe health problems. According to a recent WHO estimates, there are over seven million deaths from air pollution annually.
These estimates carry their own health warning, since they are based on statistical modelling, but the problem is undoubtedly a real one. Outdoor pollution is a particular problem for large cities in emerging economies. Air quality in Beijing is notorious, and Delhi’s is equally bad, albeit less well publicised. But pollution does not have to be man-made: fine sand particles can be equally hazardous, and made a significant contribution to the recent UK alert.
However, an even bigger part of the problem is in households in the developing world. Women and children in particular are subjected to very smoky atmospheres from indoor cooking fires, and more than half the total deaths attributed to air pollution are caused by indoor smoke.
European countries would have had similar problems around the time of the Industrial Revolution. Rapidly growing cities were a magnet for poor labourers looking for work, but they worked in harsh conditions in an atmosphere comparable to that of present day Beijing. But awareness of the problems brought calls for social reform and an improved urban environment.
Increasing prosperity brought better living standards and, ultimately, big moves to clean up both air and water. Only 60 years ago, London was a city of black buildings and recurrent smog, caused mainly by smoke from coal fires. Now, we may worry about particulates from car exhausts, but the air is incomparably cleaner than our parents had to breathe. Problems remain, but we have the resources to do something about them.
So, another recent headline prompted by the same spike in air pollution read Longer-term thinking ‘needed’ on air pollution. This story makes the point that pollution such as sulphate aerosols or carbon exhaust particulates may be a mixture of locally-generated material and some which is blown in on the wind. It is the particular set of weather conditions which determines whether a really bad day occurs.
In prosperous countries, a clean and safe living and working environment is a higher priority than in poorer ones, where people have to cope with conditions Europeans haven’t experienced for many decades. This same transition will happen in China, India, Brazil and other currently low- and middle-income countries. Continued rapid urbanisation will create more pressures, but improved technology and the availability of more resources will more than compensate.
So, it is right that we continue to improve air quality in our cities, for the benefit of ourselves and future generations, and economic growth will give us the wherewithal to do so. But in the meantime we are distracted by costly attempts to reduce another form of ‘pollution’, the carbon dioxide emissions which are deemed to be the primary driver of global warming. In truth, the jury is still out on the degree of warming and the impact this may have, but at the same time it’s very clear that CO2 is also essential for life.
Rising levels increase the amount of biomass produced by plants, since carbon dioxide is the essential feedstock for photosynthesis. And, ultimately, all animal life depends on plants as either a direct or indirect source of food. Reducing air pollution is not going to have a negative effect on any species, but cutting CO2 emissions will only be a net benefit if positive feedback and the enhanced greenhouse effect turn out to be valid assumptions. The failure of climate models based on them to predict the evolution of average temperatures over the last couple of decades doesn’t give much confidence in this outcome.
There will be no Scientific Alliance newsletter on 24 April. The next edition should appear on Friday 1 May.
Martin Livermore
The Scientific Alliance
St John’s Innovation Centre
Cowley Road
Cambridge CB4 0WS
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