By Peter Boyle
The balance of scientific opinion has swung unequivocally behind the view that industrial activities in the last century have been accelerating the greenhouse effect. What once was a radical theory — that a number of gases were building up in the atmosphere and acting like a blanket to warm the globe — has been proved to be fact. The world has been given clear notice: act now or face ecological suicide.
By the middle of last year, the world's leading scientists concluded that, although there were some uncertainties about the likelihood and character of human-induced climate change, it is certain that:
- there is a natural greenhouse effect which keeps the earth warmer than it would otherwise be.
- emissions resulting from human activities are substantially increasing the atmospheric concentrations of the greenhouse gases: carbon dioxide, methane, chlorofluorocarbons (CFCs) and nitrous oxide. These increases will enhance the greenhouse effect, resulting in an additional warming of the earth's surface.
- global mean temperature has risen between 0.3 and 0.6° C since the middle of the last century; most of this change took place in the first four decades of this century and since 1975.
The scientists' findings were summarised in the report from Working Group I of the UN Intergovernmental Panel on Climate Change (IPCC).
The reasons we are in this situation were also clear. Since the industrial revolution, the burning of fossil fuels and deforestation have increased the carbon dioxide content of the atmosphere by 26%. Methane concentrations have doubled because of rice production, cattle rearing, biomass burning, coal mining and the release of natural gas.
CFCs were not present in the atmosphere until their invention in the 1930s and then proliferated in use as aerosol propellants, solvents, foam blowing agents and refrigerants.
There is now 50% more greenhouse gas in the atmosphere than in pre-industrial times.
If no steps are taken to limit greenhouse gas emission, say the scientists, carbon dioxide levels will have doubled by 2025 and quadrupled by the latter part of the next century. Methane levels will be 1
55D>times higher and nitrous oxide will have almost doubled. CFCs (now being phased out because they destroy the ozone layer which filters out ultraviolet light) would more than double in that time.
While it is easy for scientists to determine the direct impact of these increases in greenhouse gases, various other natural processes act to amplify or reduce the resulting changes. Nevertheless, existing f nothing is done to limit emissions, the global mean temperature will rise by about 0.3° C per decade. By the year 2025, global mean temperature will have risen by about 1° C.
The global warming detected so far remains within the range of natural climatic variability, and this is seized upon by the opponents of immediate action to cut greenhouse gas emissions. We know the earth is warming and that it has done so particularly fast in the last few decades, but it won't be till the end of this century when we have the temperature measurements that prove unequivocally that greenhouse gases have increased global warming.
By then it may be too late to do much to reverse severe climatic change:
- A rise in sea level may threaten some low-lying islands and coastal areas by the middle of the next century. This would be caused mainly by the expansion of sea water as it warms.
- Agriculture in Brazil, Peru, the Sahel, South-east Asia, Asian USSR and China would be severely affected.
- Major vegetation zones could face severe disturbances, and animal and plant species will disappear because they will not have time to adjust to rapid climatic change.
- There will be major water shortages in many arid to semi-arid areas or areas subjected to heavy pollution.
- Regions currently vulnerable to natural hazards like flooding, drought, landslides, severe windstorms and tropical cyclones would be even more affected.
- There would be more deaths from heat waves, and some diseases will spread more easily with higher temperatures.
Since the IPCC report was presented, the temperature measurements for 1990 have come in. According to an article by Fred Pearce in the January 19 New Scientist, last year's temperatures topped previous record-breaking years for average world temperatures in 1983, 1987 and 1988. Three of these four years were also times of exceptionally dry conditions in the Sahel.
Unlike the three previous hottest years, there was no El Niño effect last year. El Niño is the strong natural warming of the South Pacific Ocean which lasts for a few months and influences climates around the world. El Niño usually occurs once in four years, and some climatologists are predicting one for this year, suggesting that 1991 will set a new temperature record.
Satellite pictures show less snow cover over the Eurasian land masses during this and the past two winters than at any time since records were begun 20 years ago. The region of greatest warming last year, as in the three previous years, was western Siberia.
At the World Conservation Union conference in Perth late last year, Benjamin Negeak of the Alaskan Department of Wildlife Management described a dramatic warming of coastal waters. During three weeks of July 1988, temperatures of 52° F were recorded in deep waters; around 37° F. Similar warm waters were observed in 1989.
Scientists have noticed that while most of the world has got warmer over the 1980s, Greenland, north-eastern Canada and some of the Soviet Arctic islands have become colder. Recent German research on climate models soon to be published predicts that some parts of the planet will cool during the first phase of global warming caused by the greenhouse effect.