Environmental surprises can result from many causes including unforeseen issues, unexpected events, new developments, changes in trends and shifts in environmental perception. New issues rarely appear without warning; however, their lack of frequency does not undermine their importance.
Some events may be well known but their severity, timing and location unanticipated. As populations expand and industrial activity intensifies, these events may become more common or more serious.
In the past, several unforeseen environmental issues have been brought to light by the scientific community. The best known recent example is probably stratospheric ozone depletion caused by emissions of CFCs and other ozone-depleting substances. The phenomenon was not discovered until 1974 and it took until 1985 - when the presence of the Antarctic ozone hole was discovered - for it to be accepted as a major international issue. Similarly, acid rain was not foreseen as one of the results of industrial expansion, and its discovery in the 1960s - including the first observations of its impact - was one of the critical events that led to the Stockholm Conference on the Human Environment in 1972.
The oceanic flip-flop theory suggested by several scientists since the early 1960s (see, for example, Broecker 1987) is another example. Global warming, it is argued, could interrupt the system by which cold, salty water in the North Atlantic periodically sinks to the ocean floor, a mechanism that is vital to the general circulation of the oceans and particularly to the Gulf Stream that warms much of Europe. If global warming caused increased rainfall or reduced wind speeds over the North Atlantic or led to the melting of freshwater glaciers in Greenland, salt concentrations in surface waters could fall, leading to less mixing of surface and deep waters. This would interrupt the flow of the Gulf stream, bringing a cooler climate to northern Europe. More recently, Broecker (1997) has suggested that these effects could turn off the deep-ocean conveyor belt completely, triggering an ice age. Evidence for such flip-flops has been found in geological records obtained from ice cores and deep-sea sediments. Of particular concern is the fact that these events have occurred over time periods as short as four years. Broecker refers to the oceans as the Achilles' heel of the climate system.
Current research may well bring to light other unexpected consequences of the increasing human manipulation of nature and biological processes. The possible effects of accidentally or intentionally introducing genetically-modified organisms (GMOs) on the gene pools, survival and overall health of wild populations of cultured species is an active area of research. While GMOs are expected to be widely used in the United States by the year 2000 in crops such as soya and maize, in other regions there is serious concern about the risks involved, and their commercialization has been postponed until more is known about possible impacts.
The rapid evolutionary nature of microbes, viruses and some insects is another area where surprises could be in store. Similarly, the enormous disruption that chemicals can have on ecosystems and human health is now well known. But every year many new chemicals are brought into circulation. The fact that many are introduced without sufficient research into their impacts is a major worry, as is the potential impact of mixtures of chemicals of which we currently have little understanding. More research into the whole range of chemical issues, including recently recognized topics such as endocrine disrupters, is needed.
A classic example is the chemical time bomb (Stigliani 1991). Chemicals, either produced naturally or as a result of industrial and agricultural activities, tend to accumulate slowly and harmlessly over many years in soils, sediments, lakes and other environmental reservoirs. However, when the carrying capacity of the receiving ecosystems is finally exceeded, there can be a sudden release of the chemical. Alternatively, the chemical may be released because of changed environmental conditions, as happens when harbours are dredged and wetlands drained. The environmental consequences of chemical time bombs can be severe.
Stratospheric ozone depletion was unknown at the time of Stockholm. Chlorofluorocarbons (CFCs), which were thought to be chemically inert and harmless to the environment, are now recognized as the primary cause of stratospheric ozone depletion. CFC-induced ozone depletion, first hypothesized in 1974, gained some public attention as a result of an article in the New York Times the same year but became an alarming issue worldwide following the discovery of a large stratospheric ozone 'hole' over Antarctica in 1985.
Unexpected events in the 20th century have included: a) Oil spills such as the Torrey Canyon (1967), Amoco Cadiz (1978) and Exxon-Valdez (1989) and through war, as in the Persian Gulf in 1991; b) Accidental poisonings and toxic chemical events: methylmercury poisoning, Minimata, Japan (1959); PCB poisoning (Itai-Itai), Kyushu, Japan (1960s); dioxin leak, Seveso, Italy (1976); methyl isocyanate leakage, Bhopal, India (1984); chemical warehouse fire, Basel, Switzerland (1986); c) Severe smog and air pollution events: London (1952), Indonesia forest fires (1997); d) Nuclear accidents: Urals (1958); Three Mile Island (1979); Chernobyl (1986); and e) Biological Invasions: zebra mussel, Great Lakes (1980s); Mesquite trees, intentional introduction with unexpected agricultural effects, Sudan (about 1950).