Apocalyptic visions

Global warming caused by the ever-increasing emission 01 greenhouse gases into the Earth’s atmosphere has potentially disastrous implications for much of Asia. The viability of many of the region’s staple crops — and by extension much of Asia’s economic base — is threatened, not merely by increased temperatures, but also by changing rainfall patterns. In addition, rising sea levels could inundate islands and low-lying coastal areas — which are often the most fertile while also putting further pressure on the remaining cultivatable land.

Barrie Pittock, who leads the Climate Change Impact Group at the Commonwealth Scientific and Industry Research Organisation Division of Atmospheric Research in Melbourne, said "the present rate of increase in concentration of greenhouse gases in the global atmosphere is producing an enhanced greenhouse effect, which will lead to global warming and related effects at a global and regional level."

Pittock continued: "The exact magnitude and rate of climate change and sea-level rise which can be expected depends on future human behaviour and various uncertainties in our understanding of the climate system. Nevertheless, it is likely that by the middle of the 21st century the Earth will be warmer than at any time in human history."

Acting like a greenhouse, the Earth’s atmosphere traps the sun’s rays during the day and stops heat loss at night. Few scientists and other specialists now disputes that over-dependence and use of fossil fuels that produce gases like carbon dioxide have upset the balance.

Australia’s own contribution to the greenhouse crisis is substantial. On a per capita basis, the country emits 11 tonnes of carbon dioxide, methane and chlorofluorocarbons into the atmosphere each year. This is more per head than any other nation, and nearly twice the OECD average.

While some claims about the effects of global warming border on the sensational, Pittock and his colleagues have reduced the degree of doubt involved in predicting the future climate with the use of sophisticated computer models. Using these tools, they have predicted, for example, that the southwestern region of Western Australia is likely to be drier next century as a result of the greenhouse effect while the northern and eastern parts of the continent are likely to be wetter.

The Australian Government has responded to these and similar forecasts by undertaking to reduce the country’s greenhouse emissions by 20% by 2005. The 20% figure has been contested by some environmentalists, who maintain Australia must aim at two or three times that target.

While scientists are now able to speak of the predicted climate changes with some certainty, there remain several uncertain features — notably in relation to rising sea levels, according to Pittock.

He said that because of their enormous capacity to absorb heat, the oceans will help delay global average warming by at least a decade or two. Other scientists, primarily in the US, have also suggested the eruption of the Mt Pinatubo volcano in the Philippines — which vented enormous quantities of dust into the upper atmosphere — may also contribute to short-term global cooling, especially in the tropics.

However, Pittock pointed out that changes in the oceans, including surface currents and deep ocean circulation, could introduce local and regional anomalies.

"One such mechanism of great significance to climate in southern Asia and Australia is the El Nino effect," he said. "When there is an El Nino year, we generally experience drought conditions in much of southern Asia and in northern and eastern Australia, as in 1982-83. Wet conditions usually occur in the same regions during anti-El Nino years, such as 1974-75 and 1989. At present we do not know how the El Nino effect will change with global warming and this is a major uncertainty."

Nevertheless, the Australian scientists are confident there will be a gradual rise in sea levels due to expansion of the warming ocean water and as glaciers melt. The global rise in sea levels is expected to average about 6 cm every 10 years for the next 50 to 100 years. After this period, the rate at which the sea level rises could increase as the huge West Antarctic ice sheet begins to break down. The end result would be an addition of several metres to the sea level over the next few hundred years, though some Pacific islands and other low-lying areas of the world would have become uninhabitable well before then. -

"For Asia and Australia, a doubling of carbon dioxide emission will see temperatures rise 2-3°C on coastal areas and up to 4 or 5°C inland," Pittock said.

Jeni Evans, another member of the Melbourne-based group, noted that while there is no evidence that the frequency of tropical cyclones and typhoons would increase, her research suggested they may well occur a lot further south than they do at present as well as becoming more intense.

The increased availability of moisture in the warmer atmosphere is also expected to contribute to a widespread increase in rainfall, with all the changes that would entail. Pittock put some rainfall changes at up to 20% or more, which could have profound effects on current agricultural practices and on the frequency and intensity of floods and droughts.

"Where moisture is not a limiting factor, an increase in temperature would allow some crops to be grown further towards the South Pole and at higher elevations, while lengthening the growing season at existing sites. However, some crops would suffer from extreme heat stress and horticultural crops may become unviable in areas with insufficient winter chilling," he said.

Some of Australia’s wheat strains, for example, are incapable of withstanding a mean temperature increase of 1°C without suffering substantial loss of yield. Extremes of temperature will also make efforts to reverse the huge soil erosion problems across Australia — and indeed other parts of Asia — difficult, if not actually impossible.

Over-use of chemicals, massive deforestation, introduced weeds and pests, have made Australia one of the most degraded of all continents m terms of her soils.

Predictions of future climate changes are, by their nature, open to dispute and interpretation. Differences between scientists over data and conclusions, the apathy of many governments with more pressing priorities and businesses’ generally short-term view, have often combined to make the issue one of debate and vague pronouncements rather than effective action.

However, Pittock said: ‘The enhanced greenhouse effect is a world problem, which demands both global and local solutions. We will have to adjust to that change, which is unavoidable, and work together to minimise the future rate of change." 

-Jacqueline Rees in Canberra

Source : Far Eastern Economic Review, 19 Sept, 1991

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