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On 1 March, negotiations begin for a new international treaty to limit
the damage caused to the environment by acid rain. Government scientists
from throughout Europe will meet in Geneva under the UN banner to thrash
out a successor to the 1984 agreement, which is known as the ’30 per cent
club’ because it required nations to cut their emissions of sulphur dioxide,
the main cause of acid rain, by 30 per cent.

But this time the intention is to base the deal on scientific analysis
of the impact of acid rain. The aim will be to target new cuts in emissions
of the gases that cause acid rain, to give maximum benefit to the environment.
However, this plan for a scientifically pure and economically efficient
deal is threatened by an outbreak of crude politics. With cuts in emissions
of 80 per cent or more being discussed, the stakes are high and environmentalists
are accusing the British government of using statistical devices to cover
up the extent of acid damage at home.

Ever since the 1984 deal was signed, researchers in several European
countries, including Britain, have been calculating the level of acidity
that various environments – from the lakes of Sweden and Scotland to the
coniferous forests of Germany and Austria and the heathlands of southern
England – can withstand before suffering serious harm. These thresholds
are called ‘critical loads’. Using atmospheric models to trace the acid
back to the sources of the pollution such as large power stations, the aim
is to pinpoint which emissions should be cleaned up.

European emissions of sulphur dioxide from coal and oil-burning power
stations have already been cut back drastically since 1980, partly as a
result of installing ‘flue-gas desulphurisation’ equipment to power stations
and partly by switching to other fuels, such as gas, nuclear power or wind.
The cuts have reached 50 per cent in the Netherlands and Belgium, 60 per
cent in France, Sweden and Norway, and 70 per cent in former West Germany
and Austria.

Of the major Western European nations, only Britain failed to join the
30 per cent club. Since 1980, Britain has so far made cuts of only 25 per
cent – almost all as a result of closing small coal-fired power stations
in the early 1980s. British emissions of sulphur dioxide have hovered at
a little under 4 million tonnes annually since 1983 (see Graph). Further
cuts have been delayed by the privatisation in 1990 of the electricity industry,
which has held up plans for fitting cleanup equipment to power plants such
as Drax in Yorkshire, one of Europe’s large power stations. Britain joined
other members of the European Community in signing the Large Combustion
Plant directive in 1987, which requires countries to reduce emissions to
60 per cent of their 1980 level by 2003.

But scientists from the government’s Institute of Terrestrial Ecology
in Cambridgeshire warn that even this will not be enough to bring the deposition
of acid over sensitive areas of Europe, including much of highland Britain,
below the critical loads. So members of the 30 per cent club, plus Britain,
will negotiate tougher targets this year, overseen by the UN’s Economic
Commission for Europe (UN ECE).

Meanwhile, work on a new Community directive following similar, tougher
lines is due to begin in 1994. And, following this, work will begin on setting
critical loads for nitrogen as a basis for reducing emissions of nitrogen
oxides, the other main source of acid rain .

The idea of using critical loads to set pollution limits is novel because
for the first time a major clean-up programme will be directly related to
the harm the pollution is doing, rather than to what is easily achievable.
This brings it much more in tune with the ‘precautionary principle’ promoted
by environment groups such as Greenpeace.

Sharing the load

In the past, Britain has always been guided by the philosophy of using
‘best practical means’ to reduce pollution – usually now known by the acronym
BATNEEC, meaning ‘best available techniques not entailing excessive cost’.
It is a weaker version of the German principle of applying ‘best available
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Britain helped pioneer the idea of critical loads in the mid-1980s after
arguing that there was no scientific basis for the 30 per cent club. Now
countries throughout Europe are drawing up critical load maps of their soil
and freshwater for the UN negotiations.

Britain published its first critical load maps for soil two years ago.
At the time, ministers claimed that by 2003, only 8 per cent of British
soil would receive more acid than its critical load. But a report prepared
by Andrew Tickle for Friends of the Earth last year found that the figure
had been reached by statistical sleight of hand. If Britain had used the
mapping methods adopted by other Community countries it would have reached
a figure of 47 per cent, not 8 per cent. The familiar charge that Britain
was ‘the dirty man of Europe’ was revived.

The standard definition of a critical load is ‘the highest load that
will not cause chemical changes leading to long-term harmful effects on
the most sensitive ecological systems’. The minerals in soils can neutralise
a certain amount of the free hydrogen ions (whose increasing concentration
indicates greater acidity). But beyond the ‘critical load’, excess ions
accumulate and change the soil’s chemistry. For instance, they combine with
plant nutrients, such as those based on calcium and magnesium, and leach
them from the surface soils. Once the acidity of the soil reaches a certain
level (around pH 4.5), compounds of potentially toxic substances such as
aluminium and other heavy metals are broken down, mobilising the metals
as free ions.

Aluminium is normally present in soils in an inert form, bound up in
complex inorganic molecules. But once mobilised, it will damage plant roots
and the fungi that live on plant roots and help them function. It can leave
trees particularly vulnerable to disease and other environmental stresses
such as drought.

These processes are also believed to be behind the death and dieback
(the death of young shoots) of trees across large areas of central Europe
during the past decade. Certainly, the European map of sensitive soils effectively
picks out the parts of central Europe where forest decline has been worst,
such as the Black Forest, the Alps and the mountains around the edge of
the Czech republic (see Map overleaf).

Aluminium ions may also wash into streams, killing fish; it has been
the most toxic constituent in the thousands of Scandinavian lakes that
have become acidic and fishless in the past three decades. Again, these
areas coincide with the vast area of soils and fresh waters across Scandinavia
deemed by theory to be the most sensitive to acidification.

In Britain, there is now scientific consensus that acid rain is responsible
for the loss of fish from certain streams in Wales, the Galloway hills of
southwest Scotland and the Cairngorms. But the Forestry Commission steadfastly
denies any connection between sickness among trees on its Scottish plantations,
where soils are sensitive, and where levels of acid rain greatly exceed
calculated critical loads. (Instead, it blames a wide range of disease factors.)

In 1988, a UN ECE workshop agreed a methodology for calculating the
critical load for different soils, based on the minerals in the rocks under
them. The most sensitive soils are those over granite and quartzite rocks.
These soils are often thin (less than a metre deep) and contain few minerals
that can neutralise acid, while the rocks beneath weather only slowly. The
least sensitive soils are over limestone, where the rich supply of calcium
carbonate provides an almost limitless capacity to neutralise the acid.

In practice, the vulnerability of soils to acid also depends on land
use. Land planted with coniferous forests is vulnerable, partly because
the trees’ needles effectively capture acid water droplets from passing
clouds and mist, and partly because the trees produce a layer of acid humus
on the soil surface. By contrast, most arable fields are dosed with sufficient
fertilisers and lime to neutralise acid rain.

On the basis of these assessments, soil is assigned to one of five categories,
with critical loads varying from 0.2 to 4 kilograms of free hydrogen ions
per hectare per year. Different methods of assessing critical loads have
arrived at almost identical conclusions. The main problem is the next step
– the mapping.

How detailed should the map be? Decisions to spend millions of pounds
on cleaning up pollution from large power stations cannot be based on the
need to save a small plot of extremely sensitive soil. But equally, if the
map’s detail is too coarse and omits too many small areas of sensitive soils,
the whole point of the exercise – to save the most vulnerable ecosystems
– will be lost.

Britain is accused of doing just this. Its first critical load maps
in 1981 portrayed the nation as a grid of 1-kilometre squares, each with
a critical load for its soils. Researchers from the Institute of Terrestrial
Ecology did this by identifying the critical load of the dominant soil type
in each grid square. This involved weeding out tiny patches of very sensitive
soils. But it still produced maps showing a complex picture of vastly varying
soil sensitivity, particularly in southern England.

But the problems really started when government scientists bundled together
these small squares into larger ones, each covering 100 square kilometres,
for international negotiations. Each of these larger squares is assigned
a critical load, again according to the sensitivity of its dominant rather
than most sensitive soil. The effect is to ‘lose’ many important, sensitive
ecosystems.

Other countries have approached the task differently. Most West European
countries have opted for maps that show the critical load needed to protect
95 per cent of the soils in each grid square – compared to Britain’s 70
per cent or less – so that aggregating small squares into bigger ones retains
more accuracy. Britain had chosen 70 rather than 95 per cent because ministers
thought this would give them the ‘right balance’.

Tickle calculates that 33 per cent of Britain’s land area contains
soils that are more sensitive than the dominant soil type within their
100-kilometre grid square. This figure rises to 47 per cent in southern
England, 52 per cent in Norfolk, 56 per cent in the Pennines (an area so
ravaged by acid rain that until recently, trees would not grow in it) and
59 per cent in western Scotland.

Checking the small print

Southern England is not often associated with damage from acid rain.
Its dominant soils, on the North and South Downs and the Chilterns, are
limestone and chalk, with abundant carbonate to neutralise acid rain. So
most of the region falls into the government’s least sensitive categories,
able to absorb annual acid loadings of 2 or 4 kilograms per hectare. But
the more detailed map of 1-kilometre grid squares – not presented at international
meetings or printed in handouts – shows many small but important areas where
the critical loads are 10 times smaller.

Andrew Farmer, acid rain specialist at English Nature, the government’s
statutory conservation advisers, has been plotting these ‘isolated pockets
of completely unbuffered soils’ in southern England. ‘They include acid
heaths in Surrey, Berkshire, the Weald, southern Hampshire and Thetford,’
he says. A report by Farmer last year revealed that these heaths, many of
them designated sites of special scientific interest, have already suffered
extensive damage from acid rain and will continue to do so unless the regulations
change.

There are indications that the government may go even further in filtering
sensitive environments out of the critical load maps. Maps recently presented
to the UN for discussion have used grid squares of 400 and, in one case,
22 500 square kilometres. But still only the dominant soils in each giant
square is used to assess the square’s critical load.

Following a New ÐÓ°ÉÔ­´´ news article on the issue (This Week, 5 December
1992), Lord Strathclyde, a junior environment minister, wrote to the Labour
MP Tam Dalyell defending the government’s approach. ‘It is certainly true,’
he said, ‘that aggregating data . . . makes some of the fine detail disappear,
so that small patches of high sensitivity can be lost.’ But the alternative
of ‘allowing the area of greatest damage in a square, however small, to
determine that square’s sensitivity as a whole would misleadingly suggest
that the whole square was suffering that amount of damage.’

This defence is odd. First, it seems to contradict the basic definition
of a critical load as the highest load that will not cause damage ‘to the
most sensitive ecological systems’. And it sits uneasily with the promise
in the government’s 1990 White Paper on the environment, Our Common Inheritance,
to protect ‘particularly vulnerable environments’.

Secondly, British maps of critical loads for freshwater lakes and streams,
to be published in a few weeks, will use exactly the approach the minister
says would be misleading for soils.

However, there is little risk of political embarrassment in taking this
more rigorous approach for freshwater. British lakes and streams are better
buffered than soils against acid attack. Their critical loads are higher,
probably because many are fed with water coming from deep below ground,
away from the worst effects of acid rain. However you do the calculations,
no more than about 8 per cent of British freshwaters exceed their critical
loads. But, as one scientist involved added, ‘what is sauce for the goose
should be sauce for the gander.’

However coarsely the critical loads are mapped, the largest land areas
suffering damage from acid rain still stand out. Keith Bull at the Institute
of Terrestrial Ecology says that, for the foreseeable future, critical loads
will continue to be exceeded in large parts of Wales (including Snowdonia),
the Lake District in Cumbria, Galloway and the Scottish Highlands.

In many of these sensitive areas, acid fallout currently exceeds the
critical load by between two and ten times. Only the introduction of clean
technologies to virtually every coal-burning power station in Scotland,
Wales and northern England (at a cost of £5 billion or more) could
ensure compliance.

The use of critical loads to direct reductions in acid emissions is
a major step forward in protecting the environment effectively. But the
original idea of ensuring that virtually every field, forest or heathland
across Europe received less acid fallout than its critical load is at risk.
As a UN ECE task force on modelling critical loads concluded last year,
full achievement of critical loads is ‘unfeasible for the year 2000 . .
. without considerable economic restructuring or changes in the energy system.’

Targets for critics

So now, in place of the critical load, British negotiators are talking
about the less scientifically pure idea of ‘target load’. But what kind
of targets? One idea is to halve the existing gap between current rates
of acid deposition and critical loads. Another would aim to protect just
50 per cent, rather than 95 or 70 per cent, of the soils and freshwaters
in each grid square.

Another system accepts that some areas (including much of Scotland and
Wales) cannot be brought within their critical load limit, and removes them
from the calculation. They become blank squares on the map. Alternatively,
priority can be given to reducing the acid fallout over the most sensitive
areas, and the rest can be ignored for the time being.

A meeting next month will begin to narrow down the options. The chief
scientist at Britain’s Department of the Environment, David Fisk, says the
final agreement should be signed by the end of the year. But the problem
is that, once negotiators drop the firm, incorruptible target of bringing
acid rain across the entire continent below critical loads, a fierce political
debate about what kind of target to put in its place becomes unavoidable.
With each formula producing different targets for national reductions in
emissions, and with spending of billions of pounds hanging on the decision,
the debate will be intense.

Michael Chadwick, the British head of the Stockholm Environment Institute,
has done much of the scientific ground-breaking in critical loads research.
He wonders whether, at the end of the day, the targets will lose all relation
to the original critical load calculations. ‘After a decade of scientific
discussion about how to do this better, we could simply land up with a 70
per cent club to replace the old 30 per cent club,’ he says.

The deficiencies of this politically straightforward but scientifically
inefficient approach are clear. If the continent worked towards an average
cut of 70 per cent, with the biggest cuts targeted to protect the most sensitive
ecosystems and to spend money most efficiently, this would be enough to
give roughly 95 per cent protection for the whole continent. But, a UN task
force has concluded, an across-the-board cut of 70 per cent for every country,
without targeting, would be both much more expensive and much less effective.

Such a cop-out is far from inevitable, however. With the scientists
still largely in charge of negotiations, 11 countries last year submitted
ideas for target loads for their own territories. Some targets are tougher
than others. Britain’s, based on dominant soils inside large grid squares,
are laxer than most. The task force has plugged the targets into its computer
models to arrive at rough estimates of how far emissions must fall below
the 1980 baseline to meet these national targets.

The figures appear daunting. For Britain, the target loads would require
a cut of 69 per cent. This is substantially above its current Community
commitment to a 60 per cent cut, but well below the 91 per cent that other
proposals (to bring 95 per cent of the country to within 1.5 times the critical
load) would require. In France, Denmark and the former West Germany the
tougher national targets, combined with those of their neighbours, will
require 90 per cent cuts. And in former East Germany, the biggest source
of acid pollution in Europe, the targets would require a 95 per cent cut.

These will generally be hardest to achieve in parts of eastern Europe
that use ‘brown’ coal, which produces more sulphur for every unit of energy
generated than other coals or oil. The German government would have to reduce
emissions from former East Germany, recently put at more than 5 million
tonnes of sulphur dioxide, to just 230 000 tonnes. Bulgaria, which has seen
a 22 per cent increase in emissions of sulphur dioxide since 1980, would
have to engineer a cut of 50 per cent. (The timescale is still uncertain.)

Nobody believes such reductions can be achieved in Eastern Europe without
substantial help from Western agencies such as the World Bank. In former
Czechoslovakia, and in Poland, Romania and parts of Russia, reaching the
targets would cost more than 0.5 per cent of gross domestic product over
the coming decade, compared to 0.08 per cent for France and Britain.

But some less industrialised countries, where pollution is lower and
ecosystems are less sensitive, could still increase their sulphur dioxide
emissions. Greece, which has upped them by a quarter since 1980, could hike
them by another 50 per cent; Turkey could triple them.

The science of critical loads suggests that such increases are acceptable,
though politically it might be unpalatable. And if Europe is to clean up
its air and protect its surviving natural habitats from acid attack, political
horse-trading at least as much as biological truth or the cold logic of
the print-outs from computer modellers will determine the outcome.

The remaining question though must be: why has Britain opted for such
a low standard for its critical loads, apparently sabotaging an approach
to pollution control which it helped pioneer? Privatising the electricity
industry freed its regulators to take a tougher approach to sulphur dioxide
pollution. Last year the government’s air pollution inspectors (through
Her Majesty’s Inspectorate of Pollution) successfully prosecuted Rhone-Poulenc,
which manufactures sulphuric acid, for excessive emissions of sulphur dioxide.
Might not National Power or Powergen, the privatised power generators, be
next?

But the British government has a long history of resisting calls for
tougher limits on acid emissions. And old habits die hard. Although Lord
Strathclyde said in January that ‘it is not possible to say very much at
present about the UK’s position in the negotiations’, a Whitehall source
indicates that since the 1992 general election the environment minister
Michael Howard has set his face against any commitments beyond the 60 per
cent cut already required by the Community.

The higher cost of going slow

The government’s recent decisions to shore up the coal industry and
slow down the licensing of ‘clean’ gas-fuelled power stations will increase
the cost to the electricity generators of cutting sulphur dioxide emissions.
As the Commons select committee report on the energy industry suggested
in January, the generators could in future argue that government energy
policy was preventing them from using the best practical means to reduce
emissions, and demand that the government pay for cleanup equipment. (National
Power declined to comment.)

The British approach to the UN negotiations is likely to be that individual
nations should set their own target loads for acid rain. Since about four-fifths
of British pollution falls on British soil, a lax target would then require
lower reductions in emissions. But there would still be debate about British
pollution carried across the sea – to Scandinavia, for instance.

If Britain’s neighbours, particularly Norway, set tough target loads
for themselves, Britain will have to cut its emissions by at least 70 per
cent from 1980 levels as its contribution to meeting them. At the end of
the day – with or without the science of critical loads – the acid rain
debate will look much as it did 20 years ago, with the Scandinavians complaining
about Britain’s reluctance to cut its emissions to protect the sensitive
soils and lakes of southern Norway. And, once again, the massive damage
done by British acid rain to British soil will be ignored.

* * *

A critical look at nitrates

Research into critical loads has a long way to go. The current round
of discussions will set new targets for limiting emissions of sulphur dioxide,
which form sulphuric acid in the atmosphere. But it leaves to one side the
impact of the second source of acid rain – nitrogen oxides that convert
to nitric acid in the air. Britain and several other countries are planning
to produce critical load maps for nitrate fallout.

The nitrate component of nitric acid is an important and distinct pollutant
on its own in a way that the sulphate in sulphuric acid is not. In European
soils almost all sulphate swiftly leaches out, leaving behind free hydrogen
ions which add to the acidification of the soils. But nitrogen compounds
are an important plant nutrient, often in short supply in soils. With nitrates,
a lot will be taken up by plants and only a proportion will be leached from
the surface soils. This acidifies entire ecosystems.

But, as more and more nitrogen oxides are pumped into the air over Europe,
especially from vehicle exhausts, the proportion of the total taken up by
plants falls, and that leached increases – to more than 80 per cent in
most of south, east and central England, and in Germany, the Benelux countries,
Denmark, Switzerland, Austria, former Yugoslavia, eastern and southern France,
and northern Italy, Spain and Portugal. But the complexity of nitrogen cycles
in the soil means the implications of this for ecosystems is unclear, which
has led environmentalists to question the validity of producing critical
load maps for nitrate fallout before the chemistry is understood.