Merit in acid rain, greenhouse effect

Press, 26 December 1987, Page 17

Merit in acid rain, greenhouse effect

By

NIGEL MALTHUS

Acid rain is not necessarily all bad, and nor is the expected warming of the earth through the greenhouse effect, according to two glaciologists investigating the effects of human activity on the atmoshpere. Without doubt the quality of life suffers for organisms close to acid rain sources, says Dr Paul Mayewski, for acid rain is potentially a very serious problem.

But then, there are some organisms which like the change, he says. As for the greenhouse effect, caused by increases in carbon dioxide and methane in the air, there are already indications that it will increase agricultural productivity, says his colleague, Dr Berry Lyons. That comes about because plants like both the higher temperatures and the increased abundance of carbon dioxide itself.

That may be little comfort to coastal dwellers who might lose their land if warming brings melting of the polar ice caps. Entire countries, like low-lying Bangladesh, could disappear. But the point the scientists, are making is that no-one knows for sure what the "normal” climate of this planet is, and indeed, whether there is such a thing as “normal."

Those are questions they hope to answer through their work in Antarctica, Greenland, and other areas where snow and ice accumulate. Ice, they say, is the only medium on Earth capable of giving an accurate record of climatic changes over the cenUPes. .

The two men are members of the Glacier Research Group, a part of the University of New Hampshire’s Institute for the Study of Earth, Oceans and Space. They have just returned from Antarctica, where they have reconnoitred the Newall Glacier, not far from New Zealand’s Vanda Station, for a project that will give a record of the area’s climate over the last 2000 years. They will return next summer, drill a core of ice 250 m deep, and analyse its chemical composition. The deepest ice will have been deposited about 2000 years ago, giving a “snapshot” of the precise composition of the atmosphere at that time. How the composition changes through the core to the most recent layers will give a continuous record of atmospheric changes over time. Taking such ice cores is not new, though the pair say scientists from other disciplines have only recently realised that it is one of the most powerful tools available to them. Cores have been taken from the Beardmore Glacier, somewhat nearer the South Pole than the current site, and from Greenland and the Himalayas. Valuable information could also come from glaciers high in Irian Jaya and South America, says Dr Mayewski. He is also involved in a joint American and European proposal to drill a deep core, about 3000 m, into the Greenland icecap within the next few years. Ideally, he like to see a

multinational effort to take a core all the way through to bedrock. It would give a record going back half a million years.

The ice is tested for about 15 chemicals, such as the sulphates and nitrates which are components of acid rain.

Their levels have gone up tremendously in the last few years, said Dr Mayewski, particularly in the Northern Hemisphere. They are regarded as largely a record of human activity, and scientists have made predictions of how they will change with time based on various models.

The Greenland samples have come “very, very close” to the predictions and so have confirmed the models, he says. Human activity shows up less in Antarctica, at least in that chemicals like sulphates and nitrates are rare, even now. But there has been a marked warming, possibly man-made, through the greenhouse effect. The warming is obvious at the surface, with thinning ice and rising levels on Antarctic lakes. Dr Mayewski says Lake Vanda, for one, is rising “rapidly” and could force the D.S.I.R. to move Vanda Station.

Warm periods in the past, if there were any, will also show up in his ice cores, so next summer’s project should be able to determine whether the warming is cyclic or unique. Being nearer ths edge of the

continent, next year’s core will show such fluctuations better than the Beardmore Glacier core.

Dr Mayewski says that it was widely thought, 20 years ago, that the Antarctic was very stable.

“Particularly in coastal areas, that’s not true at all.”

Their work should also be able to determine whether the Antarctic ozone “hole” has happened before — if so, it could cause scientists to rethink the causes of the present depletion.

In the relative absence of man-made sulphates in Antarctiica, natural sources such as volcanoes show up well. The Beardmore Glacier record shows a big peak in sulphates in 1883 — undoubtedly from the Krakatoa eruption. Another peak in 1815 is attributed to Tambora, another Indonesian volcano. “With the new core, we should be able to document the history of Mount Erebus over the past couple of hundred years,” says Dr Mayewski. Natural nitrates come from

less well defined sources. A peak occurred in 1604. Dr Mayewski says one theory links that with solar activity, or the Kepler Supernova which was observed about that time.

Oddly, a “giant” peak occurred the year before the Krakatoa eruption. Whether there could be any link is “unclear,” he says.

Nitrate levels have increased tremendously in recent decades, ahead of any other chemical species studied. Exactly why is not yet clear. It could be something of only local or regional significance, says Dr Mayewski. Dr Berry Lyons’ speciality is studying radioactive isotopes trapped in the ice record. Natural radioisotopes, such as lead 210, from radioactive decay in rocks, and beryllium 7, from cosmic-ray bombardment of the atmosphere, give clues not only to the past climate, but where air masses have come from.

Man-made isotopes, from nuclear bomb detonations, allow accurate dating of the cores and assessment of accumulation rates of the snow.

Dr Lyons says one of the exciting aspects of their plans to take cores from glaciers in Irian Jaya and South America, is the information they hope to gather on the El Nino and Southern Oscillation. It will be one of the few ways available to study the history of those phenonema, he says.

Dr Mayewski adds that it is now known that the El Nino effect is linked with other meteorological phenomena such as the monsoon.

It has even been suggested that a series of very severe winters experienced by North America through the mid-1970s was linked to the size of the ice mass in the Tibetan Himalayas during the same period. Clearly, the world’s weather patterns are intertwined with each other, and possibly with man’s activities in ways which even now may be unsuspected. It is therefore important to get an accurate record of past fluctuations as far back as possible. Carbon dioxide levels, for example, are known to have been rising for many years — apparently because of the burning of fossil fuels since the Industrial Revolution.

If their work confirms a fairly steady, low level of carbon dioxide in the past, then a recent marked increase, “we can at least postulate that it’s something we’re doing,” says Dr Mayewski. On the other hand, it might reveal that the Earth is near the top of a peak in a regularly occurring roller-coaster ride, in which case carbon dioxide levels might be expected to naturally decrease again in the future. "We have a good chance of telling the difference between natural and human changes,” says Dr Mayewski. “Most importantly, it allows us to put ourselves in proper perspective.” Dr Lyons adds that ice records will give the best history of the effects of human activity on the planet. “Whether it’s good or bad remains to be seen.”

Documentation on Mt Erebus