A reassessment of the status and trends of desertification was called for as part of a general assessment of progress in the implementation of the United Nations Plan of Action to Combat Desertification, seven years after the UN Conference on Desertification (UNCOD) in 1977. Because of the inadequate data existing at the country or state level, the basic generalization has been set at a wider regional scale. The new assessment has confirmed the global scale of the problem of desertification as presented to UNCOD, and has increased the area and populations considered to be at risk through its recognition of the threat of desertification in the sub-humid tropics. The threatened area of 4,500 million ha constitutes 35% of the land surface of the Earth, with almost 20% (850 millions) of the world's total human population. Estimates indicate that, of this area, 75% is already moderately desertified, and 30% is severely or very severely desertified.

The rural population affected by severe desertification totals some 280 millions, or 470 millions if the urban component is included, with, respectively, 135 millions and 190 millions severely affected. These are significantly larger than the figures presented to UNCOD—mainly through the inclusion of additional sub-humid land in this assessment, but partly through national population increases and growth in the extent of severely desertified land. Both in terms of areas and population affected, the so-called developing regions are shown to be those worst-hit by desertification; and within these, the tropical semiarid and sub-humid lands tend to be the most ‘critical’ areas.

Despite all that has been accomplished with an uncoordinated global programme, the exaggerated expectations following UNCOD have not come close to being realized. Land degradation continues widely, even though in places dunes are being stabilized, trees planted, and there is some success in reducing salinization of irrigated land. Too little effort is directed towards field control of desertification. All of the indirect contributions to desertification control (education, research, training, increasing awareness, assessments, etc.) will, presumably, assist in combating desertification in the field at some time in the future. It appears certain, however, that there will be no dramatic improvement by the year 2000 unless there is far more focusing of efforts on field projects than at present. Here the activities of NGOs and some governmental agencies are to be appauded but should also be multiplied and strengthened—wherever possible with community involvement and adequate incentives.

Much attention within the scientific community has focused on the effects of a possible increase in atmospheric carbon dioxide. The impact of the increase in the CO2 content of the atmosphere is usually discussed in terms of global averages. Little information has been presented on what the regional effects of a CO2-induced global warming might be. Recent attempts at identifying local effects of such a warming suggest that, as the atmospheric CO2 content continues to rise, there will be an increase in the frequency, duration, and severity, of droughts in the United States Great Plains.

Agricultural activities in the Great Plains today are highly dependent on water drawn from the underlying Ogallala Aquifer. Yet, there is great concern that the water is being drawn out at rates that far exceed its natural rates of recharge. While the Aquifer's thickness and rates of drawdown differ at different parts of the Great Plains, some regions are already in precarious positions because of the depletion of their portion of the Aquifer.

The massive ‘bleaching’ (loss of zooxanthellae) and death of reef corals that occurred in one area (Gulf of Chiriquí) on the Pacific side of Panamá and in the Galápagos Islands during February—April 1983 continued in these areas until September—October 1983, resulting in a catastrophic disturbance. Similar episodes have been reported subsequently throughout much of the tropical eastern Pacific region (Costa Rica, the entire Pacific coast of Panamá, and Colombia), in the central and western Pacific Ocean, in parts of the western Atlantic Ocean (Caribbean coasts of Costa Rica, Panamá, and Colombia), and in the Florida Keys and Bahama Islands.

An account is given of the work on the forests of Viet Nam of the US Academy of Sciences' Committee on the Effects of Herbicides in South Viet Nam during 1971–74. Owing to the insecure state of the country at the time, very little work on the ground was possible. The Committee's conclusions had therefore to depend largely on observations from the air and aerial photography, and were subject to considerable errors.

The appearance after herbicide spraying of the Inland and mangrove forests as seen from the air in 1971 and 1972 is described. In the Inland forest most of the emergent trees were killed, but much of the undergrowth remained alive. In addition to the effects of herbicides, the Inland forests suffered widespread damage from bombing and other military operations. In the mangrove forests, herbicide spraying destroyed almost the whole biomass, resulting in the complete denudation of vast areas of soft sediments.

The effects on Boulder County, Colorado, of a major nuclear war are predicted. Although many of the effects of such a horrific event would be global in nature, the direct ones on Boulder County were considered in terms of being primarily due to three one-megaton blasts in Denver, situated 40 km to the south-east. Under assumed wind conditions, agricultural crops would be contaminated with radionuclides for prolonged periods, rendering them dangerous for human consumption. Loss of animal life, flooding, increased sedimentation, and extensive soil-erosion, should also be expected. Recovery times for environmental systems are difficult to predict. Indeed, unknown synergistic effects and global changes in atmospheric conditons might preclude eventual recovery.

Although numerous assumptions were made in these predictions, and the impacts described are scenario-dependent, the implications are clear: even if Boulder County received no direct hit, a nuclear war would have a devastating impact on the environmental systems that were considered.

The prognosis from this study and others for human societies and involved ecosystems in the event of nuclear war is grim. We hope that continued research and dignified publicity of results on the effects of nuclear war will increase the urgency with which solutions to the nuclear dilemma are sought.