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November/December 1997 issue	In this issue Table of Contents Editor's Notebook Feature: Mussel bound Feature: Global warming Write to Know À la carte Our Home and Native Tongue

Sixteen years ago, I wrote an article for this magazine titled "Confusion about climate" (Dec '81/Jan '82). Rumours of hostile climate change had unsettled public opinion and led to confusion because the experts did not agree. Most seemed to be saying that the buildup of carbon dioxide from burning coal, oil and natural gas would warm up the earth's surface, perhaps to an unmanageable degree. But only 10 years previously, the talk had been about a new ice age. Which view was right? Or did the truth lie elsewhere?

Since then, the experts have moved nearer to consensus that the world is warming up and that it will warm a good deal more. There are still dissenting voices, but most qualified people think that a warming is in progress as a result of human action — and that we must, somehow, stop it. This view is shared by many biologists and oceanographers. Even the business community has begun to consider the hitherto inconceivable — that past experience may not be a sound guide for future decisions.

How was this change of mind achieved? First and foremost, by a mountain of research in all disciplines concerned, coupled with widespread media coverage. Climate has become fashionable. It has even penetrated political consciousness, as the December meeting in Kyoto, Japan, attests. Most of all, the change has been due to superb orchestration of effort by the Intergovernmental Panel on Climate Change (IPCC), a body set up in 1988 by the World Meteorological Organization and the United Nations Environment Programme. IPCC has effectively mobilized the world's scientific community and has issued two authoritative assessments that have had major impact. In addition, the 1992 UN Conference on Environment and Development in Rio de Janeiro endorsed the Framework Convention on Climate Change that urged signatories to prompt action, the object being to limit climate change so as not to damage the biosphere and harm human well-being. At the December meeting in Japan, world policy makers will gather to take stock of what has been learned since 1992 and to consider emission reduction requirements beyond the year 2000.

So, what do scientists largely agree on? First, that greenhouse gases — chiefly water vapour, carbon dioxide, methane, nitrous oxide and ozone — act like a blanket around the earth, keeping surface temperatures at levels comfortable for life. Increasing greenhouse gas concentration (as we are currently doing), in effect, adds another blanket, warming the surface still more. The rise in the most important agent, atmospheric carbon dioxide, is mainly caused by increased fossil fuel burning — coal, oil and natural gas — as well as the clearcutting of forests, a significant storehouse of CO2. Human economic activity, such as forest burning and clearance, vehicle emissions, industrial plants and heating systems, has led to increases in heating of the lower atmosphere. Only reduced emission of these gases can stabilize the situation.

Along with this bad news, the IPCC also identified a process that may slow down greenhouse warming. Sulphur dioxide emissions from industrialized regions lead to the formation of sulphate particles. These particles create haze layers, and may increase the reflectivity of clouds, thus reflecting back incoming sunlight and cooling the surface. As well, sulphur dioxide emissions from volcanic eruptions (like el Chichón in Mexico and especially Mount Pinatubo in the Philippines) rise into the stratosphere where they may again form haze layers across the planet that last for several years, reflecting back the sunlight. Whereas industrial sulphur dioxide produces mainly short-lived, regional cooling, volcanic emissions may cool the earth for years. The combined effect of particle injections, industrial and volcanic, may have substantially reduced global warming.

Even so, IPCC's second assessment, in 1995, predicted an increase in global warming in the range of 1 degree to 3.5 degrees by the year 2100, with a best estimate being 2 degrees. While well below earlier expectations, they are still enough to seriously impact ecosystems, crops, sea levels, glacial ice and climate. Only draconian measures, partially spelled out by one of IPCC's working groups, can prevent this. Such measures will be politically difficult and will raise objections in the short term. In particular, they will affect two groups: the major international energy producers and developing countries such as China and India, which are accelerating their industrial growth with coal as an energy source.

It has been engrossing to watch the changes in climate, which began to accelerate a year after my birth in 1919. World temperatures, as measured by several groups, have risen by about 0.5 degrees in the past century — not a large figure, but still formidable for ecosystems and the world's food supply. In Canada they have risen, on a spatially uneven basis, by just over 1 degree in the past century. Some areas on the Atlantic shoreline have escaped this warming, although the Saint John Basin, in New Brunswick, Quebec and Maine, has warmed as much as the rest of the country. Most affected has been the Mackenzie Basin, the upper reaches of which have seen a century-long warming of 1.5 degrees.

Moreover, the elaborate numerical models that predict future climates (on which IPCC based its forecasts) show that the amount of warming in the interior of North America will be one of the highest in the next century. The Canadian general circulation models confirm this estimate. Our vast prairie farming economy and that of southern Ontario may face warmings and desiccations that will require drastic changes in crops and farm practices. The same should be true of forestry, especially because of altered snow cover, fire damage and insect infestation.

The trouble with the models now in use is that they give only generalized results, on a broad spatial scale. There is little or no reliable detail on the smaller scale so necessary for action by, for example, provincial governments and hydraulic engineers. So the hunt is on for ways to increase the accuracy of our models on smaller scales and our ability to predict climatic variability in the broad warming trend.

I have lived through the beginning of the computer age and the launch of satellites, both of which have transformed our science. The most dramatic change between 1992 and today is not the better understanding of atmospheric climate, but the realization on all sides that climate matters, vitally, and that it is the responsibility of many scientific and social disciplines as well as government, industry and commerce. Today there is impatience to find some firm answers. I hope that those attending Kyoto will have as vivid and broad a perception of climate as I have had. If you are ready for it, climate can be a friend — and a deadly enemy if you are not.

F. Kenneth Hare, recently retired chancellor of Ontario's Trent University and professor emeritus in geography at the University of Toronto, lives in Oakville, Ont.

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