Research over the past century has shown that the rates and magnitudes of climatic change constitute a continuum. Changes have now been identified in the climatic record that range in duration from interannual through decades and centuries to the multi-millennial time-scale. Examples range from the drought years of the 1930 and 1970 decades to the ponderous comings and goings of the ice-ages. More recently it has become clear that some changes can be quite rapid. In recent decades great progress has been made in identifying the causes of climatic variation.

The present understanding of the causes of climatic change emphasizes continental drift (or ‘plate tectonics’) at the million-years' scale, with pulses of plate movement producing significant bursts of volcanic activity that may act on the millennial or century scale. At the multi-millennial scale there is growing agreement that the variations in irradiance of the Earth, resulting from slow changes in the Sun-Earth geometry (the so-called Milankovitch variations), exercise the operative control on the timing of ice-ages and interglacials. At the decadal and interannual scales there is less agreement; but there is at least a body of research which suggests that significant volcanic activity is a contributing factor. There is considerable agreement—but little direct evidence—that anthropogenic causes such as increased carbon dioxide and other Man-made or-enhanced trace gases in the atmosphere, will be important in the coming decades.

Cultural responses might be expected to differ across this continuum. To assess the expected response to a climatic variation, one must know at least the shape of the response surface.

There is probably a critical threshold combination of climatic change magnitude and duration. Human cultures seem to be adapted to frequently-occurring short ‘aberrations’ from the expected climate. Some evidence indicates, on the other hand, that relatively small changes of climates (of the order of a century in duration) have been associated over the past 8,000 years with cultural changes that proved large enough to lead to different names being assigned in perhaps half of the cultural termini identified. A climate model which includes the effect of volcanic aerosols, suggests that most of the climatic changes associated with these globally synchronous cultural termini are related to peaks of volcanic activity. Some apparently catastrophic events have been recognized in this connection.

There remains the problem of assessing, in realistic terms, the impact of large-magnitude climatic variations on modern human societies. Of particular concern is the effect of climatic events associated with very large-scale short-term insertions of aerosols into the atmosphere. It is likely that non-equilibrium models of the atmosphere, with specified sea-surface temperatures, would give realistic results if refined to the degree that they could replicate events of lesser magnitude which have occurred in the past century. At present there appear to be no models in which the formulation of the radiative effect of aerosols or gases gives a good match with observed radiative effects. It seems that much more research, including field experiments, will be needed if science is to supply reliable advice to society on the nature of coming climatic changes.

Human activities in Nigeria are not evenly distributed on the land surface, owing to marked differences in climatic, geological, demographic, and cultural, factors in different areas of Nigeria. The use of land is designed to optimize resources for diverse interest-groups, thus causing pressures to be exerted on the land in varied degrees. Because land-uses are neither influenced by capabilities of existing resources nor based on effective land-use policy, the economic development of land is not conducive to conservation of the environment. Indeed, the attempt to maximize the use of resources constitutes a serious impediment to future development, as most lands are either destroyed or rendered marginal for primary production.

However, the best use to which land can be put is ultimately largely a political matter, and this is influenced by socio-economic factors at work in a given environment. Unfortunately, when the use of land is not in harmony with ecological approaches to development, the soils commonly depreciate to counter-productive levels. This is why, when land uses are in opposition, they pose serious questions regarding the extent to which they can adequately sustain life. There is plenty of evidence that the rate of forest depletion in the country may increase in relation to population increase, which is why, without adequate measures being taken, constraints in land-use could lead to shortened fallow periods, reduced crop-yields, overgrazing, indiscriminate burning of vegetation, excessive hunting, poor techniques of mineral exploitation, and application of unconserving agro-technical practices for food production.

In the face of the above problems, however, adoption of alley cropping by smallholder farmers, establishment of woodlots for fuel-wood production in the vicinity of large towns, planting of timber trees in the periphery of cocoa and oil palm plantations, private-sector participation in reafforestation, and rehabilitation of mined areas with suitable vegetational forms, are some of the strategies that can reduce the rate of forest depletion in the country.

Four grassland types at Cherrapunji, in northeastern India, namely the Osbeckia, Arundinella, Ischaemum, and Eragrostiella, types, were studied for soil nutrient losses through their hydrology and related soil-fertility changes. Losses through water and the consequent soil-fertility depletion were shown to be related to the frequency of the burn to which these grasslands are subjected. The Ischaemum type, with regular burning at 2-years' intervals, was the most adversely affected, compared with the Osbeckia type, which had not been burnt for the past 6 years.

In all the grassland types which were studied, the losses through water were high during the early part of the monsoon period, owing to the poor vegetation cover at that time. A desertified site with the Eragrostiella type of grassland had the lowest soil-fertility level, and had losses through removal in water that far exceeded the prevailing soil-nutrient level.

Fire can help in stabilizing the seral grassland vegetation if the soil is sufficiently deep and the frequency of the burn is not too great. On the other hand, too frequent perturbations by fire are apt to result in a desertified landscape that is difficult to restore.

The 71 hectares mainly of rain-forest on Bukit Timah Hill have been isolated for more than 130 years. During most of this period, the forest has received some form of protection: initially for climatic reasons, then as a forest reserve, and finally as a Nature reserve. It has also suffered a great deal of disturbance from illegal logging, firewood collection, hunting, wartime shelling, and recreational activity. Despite this, the Reserve still supports an immensely rich flora and fauna, although many bird and mammal species have been lost.

The example of Bukit Timah suggests that, contrary to most predictions, small rain-forest reserves can play a significant role in biological conservation, as well as satisfying educational and recreational needs.

The Kirby Canyon Conservation Agreement was designed to provide protection of the Bay Checkerspot Butterfly (Euphydryas editha bayensis) while allowing development of an extensive solid-waste landfill in the habitat of that threatened subspecies. Elements of the programme include 1) biological research; 2) habitat acquisition; 3) habitat management; 4) restoration and revegetation activities; and 5) off-site recovery, including reintroduc-tion of the Butterfly into an unoccupied suitable habitat.

The high likelihood of success of this agreement reflects the availability of detailed life-history information, the known ecological characteristics of the Butterfly, and the geographic scale of the proposed development. This agreement should provide a useful model for the resolution of potential conflicts between endangered invertebrates and resource development in urban corridors elsewhere.

Amami Oshima (Island of Amami) in Japan has five species and two supspecies of animal wildlife that are designated as natural monuments by the national government. However, government subsidy has indirectly induced population decline of some of them through habitat destruction. Self-supporting industries make up only a small portion of the whole economy of Amami Oshima, so that financial support from the national and prefectural governments has been necessary to create a large number of jobs for local people.

Forestry has been subsidized by the central governments to a large degree. As a result of cost-reduction in logging through the subsidy which has been devoted mostly to construction of logging roads, most original forests have been replaced by young secondary forests and logged areas in the central part of Amami Oshima, where all the wildlife taxa under consideration are to be observed at present. The governments have planned to manage these young forests with a 35–40 years' rotation-cycle for pulpwood, of which the commercial value is relatively low.

Of the involved seven species and subspecies, the Great White's Thrush (Turdus dauma amami), Owston White-backed Woodpecker (Drendrocopos leucotos owstoni), and the Long-haired Rat (Rattus legata), appeared to be so dependent on mature forest (uncut for at least 40 years after selective felling) that they will probably not be able to maintain their populations if all the old forests are cut down. Small populations of the Ryukyu Robin (Erithacus komadori) may be able to survive in young secondary forests, but population decline will be substantial through the decrease in the area of mature forest. On the other three species—the Amami Rabbit (Pentalagus furnessi), Purple Jay (Garrulus lidthi), and Spinous Rat (Tokudaia osimensis)—the effects of clear-cutting of the mature forests are less obvious. Further decreases in the area of mature forests will probably cause a significant reduction in the present population-level of the Amami Rabbit, but negative effects of logging on the other two species should not be very serious. An increase in the length of rotation-cycles, and changes in the use of the subsidy, are proposed for improving the wildlife habitat and the economic efficiency of local forestry.

An approach to planning, research, and management, that relates people to ecosystems of which they are part, is described and related to the Canada-United States Great Lakes Water Quality Agreements of 1972, 1978, and 1987. Factors favouring the development of an ‘ecosystem approach’ in the Great Lakes Basin include: a shared, highly valued resource; the long residence-times of ‘conservative’ pollutants in the Lakes; use of the Lakes for drinking-water supplies by c. 23 million people; threats to the integrity of the Lakes (pollution, water diversion); advances in ecosystem theory; the rise of voluntary membership associations with interests in the resource; institutional arrangements for managing nationally shared resources; and common economic ties and cultural heritages.

The principal obstacle to implementation of an ‘ecosystem’ approach in the Great Lakes Basin is the lack of policies for comparable approaches in the political jurisdictions surrounding the Great Lakes. The principal obstacle to global implementation of an ‘ecosystem’ approach is the lack of international institutional arrangements for joint advice and operational capabilities in respect of the management of nationally shared resources. Another impediment is the widespread egocentricity of governments, corporations, individuals, and the general public.