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Comments on part 2
My first comment concerns the relationship between the two topics dealt with in chapters 5 and 6, that is, the possible impacts of land degradation (as a result of deforestation and desertification) on the global climate system and the possible impacts of climate changes on the processes of deforestation and desertification (see Hulme and Kelly, 1993). Apart from the role of deforestation in the global carbon cycle and its adding to the atmospheric load of carbon dioxide, land degradation impacts on climate relate to several processes:
1. Desert and decertified territories are sources of atmospheric dust, which modifies the scattering and absorption of solar radiation in the atmosphere. Its effect on temperature would depend on the altitude at which it is borne (Bryson, 1972). The climatic impact of suspended particulate substances in the atmosphere may be no less than that of other pollutants, including the greenhouse gases.
2. The effects of an impoverishment of plant cover on the ground surface energy budget and the temperature of near-surface air have been the subject of many studies (Jackson and Idso, 1975; Balling, 1988, 1991; Schlesinger et al., 1990). Two processes are involved: increased surface albedo (especially with desertification) and reduced removal of moisture by evapotranspiration (reduction of plant cover).
3. The reduction of plant cover reduces the roughness of the surface. Surface roughness (tree growth in moist territories or scrub growth in drylands) exerts a "drag effect" that dissipates wind energy. Numerical models indicate that a less rough surface could diminish rainfall (Hare and Ogallo, 1993).
4. There is evidence indicating that reduction of plant cover reduces the availability of organic particles in the atmosphere. These particles are potential condensation nuclei and their reduction may cause a reduction in rainfall.
5. It has also been suggested that much of the rainfall in Africa's arid and semi-arid inland territories derives from nearby forested regions (e.g. the Zaire-Congo basin); deforestation reduces rainfall and exacerbates aridity further leewards.
My second comment relates to the global balance of outputs and sinks of carbon dioxide and related greenhouse gases. The world's drylands (about 40 per cent of the land surface of the ice-free earth) contribute very little to the sink capacity of the earth. Desertification further reduces this contribution. But drylands provide the available space for enhancing the global sink capacity. Programmes of afforestation and revegetation for combating desertification and reclaiming decertified areas would entail the expansion of the global sinks for greenhouse gases.
One aspect common to both deforestation and desertification (degradation of biota) is loss of biodiversity. This is evident in deforestation especially in tropical forests and woodlands. Here a wealth of species (known and unknown) are lost daily. The number of species to be lost in the world drylands is less; but many crop (wheat, barley, sorghums, millets, etc.) and fodder (medicagos, trifoliums, etc.) species that form the backbone of world agriculture and pasture husbandry have their origin in arid and semi-arid territories (Vavilov, 1949; Barigozzi, 1986). Hundreds of wild species native to drylands are sources of valuable medicinal materials (UNESCO, 1960). The loss of populations of these plants and their wild relatives represents a loss of valuable genetic materials. The impact of desertification on the loss of germplasm resources may be, from the economic aspect, no less severe than the impact of deforestation.
When we discuss issues of climate changes (chap. 5) and deforestation and desertification (chap. 6) the issue of what is a global environmental problem poses itself. The Inter-governmental Negotiating Committee for Elaboration of an International Convention to Combat Desertification (Geneva session, 13-24 September 1993) spent some time debating whether desertification was a "global environmental problem," and hence whether or not projects for combating it would qualify for support by the Global Environmental Facility (GEF).
Botkin (1989) and Turner et al. (1990) differentiate between two classes of global environmental issues: systemic and cumulative. Systemic global issues affect a physical system: its attributes at any locale can affect its attributes elsewhere because they influence the global state of the system. These need not be caused by a worldwide scale of activity. Examples include climate change and depletion of stratospheric ozone. The causes may not be global but the effects are. In cumulative global issues, the causes are geographically widespread and the impacts are also worldwide. Examples include land degradation, deforestation, desertification, population, and urbanization. As I have noted, desertification and deforestation qualify to be included in both categories because they are geographically worldwide and they may influence a physical system (the global climate).
Forest degradation goes back to the early history of humankind. Fire was an agent that inadvertently extended human impacts beyond the initial site. The impacts accelerated as population pressures increased (with the expansion of agriculture) and as world needs for timber and other forest products escalated. Matthews (1983) estimates the total area of world forests in the pre-agricultural era at 46,280,000 kmē) the FAO (1991) estimates the present area of world forests at 36,245,000 kmē) which represents a loss of 10 million kmē) of forests in all continents and in all climatic regions. Land degradation in the world drylands is the result of excessive human pressures (overgrazing of rangelands, overcultivation of rain-fed farmlands, mismanagement of irrigation and drainage systems in irrigated farmlands, over-cutting of woodlands, etc.). Dregne et al. (1991) give the following estimates of the extent of degradation:
|World drylands||61.5 million kmē|
|Agriculturally used drylands||51.6 million kmē|
|of which: degraded||35.6 million kmē|
Degraded agriculturally used drylands prevail in all world continents.
Here we have examples of worldwide problems that directly undermine the life-support system of billions of people and that indirectly affect the whole globe.
There is, however, one element of difference between the climate issue and the land degradation issue that needs to be considered when world policies are set. For instance, the world community found it suitable to address the former issue with a United Nations Framework Convention on Climate Change. Would it be suitable to address the desertification issue with a framework convention, or do we need an action-oriented convention? There are evident differences between the two issues. First, the climate change issue is still shrouded in uncertainties, including new uncertainties identified in the IPCC report published in 1992 (Houghton et al., 1992), that is, after the Convention had been elaborated (see also section 7 in chap. 5). Secondly, the damaging impacts of climate change (global warming and its consequences) are foreseen as likely to be manifest within 5070 years. By contrast, desertification is an actual menace that has been actively occurring during the past 50 years, is already damaging the life support system of some 900 million people, and is associated with recurrent droughts that have caused the loss of millions of head of livestock in Africa and the uprooting of millions of people, who flee their homelands and swarm across political borders (10 million environmental refugees in Africa in 1984/85). Here, action is urgently needed.
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Balling, R. C. 1991. "Impact of desertification on regional and global warming." Bulletin of the American Meteorological Society 72: 232-234.
Barigozzi, C. (ed.). 1986. The Origin and Domestication of Cultivated Plants. Amsterdam: Elsevier.
Botkin, D. B. 1989. "Science and the global environment." In: D. B. Botkin et al., Global Change. New York: Academic Press, pp. 1-14.
Bryson, R. 1972. "Climate modification by air pollution." In: N. Polunin (ed.), The Environmental Future. London: Macmillan, pp. 133-174.
Dregne, H. E., M. Kassas, and B. Rozanov. 1991. "A new assessment of the world status of desertification." Desertification Control Bulletin, no. 20: 6-18.
FAO (Food and Agriculture Organization). 1991. "Protection of land resources: Deforestation." UNCED Prepcomm., 2nd session, Doc. A/CONF. 15/PC/27.
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Hulme, M. and M. Kelly. 1993. "Exploring the links between desertification and climate change." Environment 35(6): 5-11, 39-45.
Jackson, R. D. and S. B. Idso. 1975. "Surface albedo and desertification." Science 189: 1012-1013.
Matthews, E. 1983. "Global vegetation and land use: New high-resolution databases for climatic studies." Journal of Climate and Meteorology 22: 474-487.
Schlesinger, W. H., et al. 1990. "Biological feedback in global desertification." Science 247: 1043-1048.
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