(This text will be soon updated)
>From ecological point of view deforestation is the most serious global environmental problem because it has been estimated to cause as much as 70% of extinctions of species; 20% is due to spreading of new species and only 10% is due to pollution . Human activities have accelerated natural extinction rate by 10000 . Tropical forests embrace at least 50%, possible even 90% of the biodiversity of the world in only 6% of its area [3,4,5]. At least 50000 species per year (i.e. equaling the total biodiversity of Finland) become extinct as a result of destruction of their tropical forest habitats [6,7].
In addition to reduction of biodiversity, and related ecological and economic values, the loss of tropical forests reduces rainfall and increases carbon dioxide in the athmosphere, i.e. strengthens the greenhouse effect. Tropical forest soil is especially vulnerable to erosion, desertification [3,5].
Temperate and boreal forest area has changed little in recent decades but 3.9 Mkm2 of tropical forests were cleared between 1860-1978 and further 2 Mkm2 between 1978-1990 (forest areas in 1990: temperate and boreal 16.9 Mkm2, tropical 17.4 Mkm2; all figures include both closed forests and open woodlands) . Destruction rate is, thus, rapidly increasing. Closed moist tropical forests (about 8 Mkm2), that are both the most diverse ecosystems and the most endangered, are currently being lost at little under 2% annual rate (142,000 km2 in 1989) Á whereas in 1980 the rate was only 1% [5,8]. It has been estimated that human activities have so far destroyed about half of tropical forests.
The main cause of deforestation is population pressure induced short cycle shifting cultivation, which very quickly results in permanent loss of soil nutrients, i.e. erosion. It accounts for 70% of forest losses in Africa, 49% in Asia and 35% in Latin America, globally about 60% (incl. all tropical forest types). Important causes for losses of particularly moist tropical forests are industrial logging, especially in South-East Asia and Brazil (45,000 km2), cattle grazing and ranching, especially in Latin America (15,000 km2) and infrastructure construction (roads, dams, etc., 12,000 km2). Wood production in developing countries is primarily used as fuelwood (75%); only 25% is used in industry. Fuelwood cutting results in 20,000 - 25,000 km2 (little less than the area of Belgium) annual loss of tropical forests (all forest types) [3,5,9].
Tropical forest conservation efforts must emphasize agricultural and population policies. This writeup, however, will concentrate on a simple and cheap technical tool, a solar cooker, which has a potential of directly affecting 10% of the problem by replacing fuelwood as a cooking energy with utilization of solar energy. Indirectly the main problems can also be addressed. Other technical solutions addressing these problems are improved stoves and biogas plants.
About 2 billion people, over 1/3 of world population, have daily dependence on fuelwood as a source of their cooking and heating energy . They live in the tropics, in the most favorable areas for solar energy utilization.
A French non-governmental organization Synopsis was asked by UNISEF to evaluate the global usage potential of the solar cookers . They estimate that 80% of fuelwood consumption in the developing countries is used for cooking. They assume that 36% of this could realistically be expected to be replaced by solar cookers. Wood savings would be 246 Mtons annually, worth $20 billion. Potential market of the solar cookers is some 200 M units, $18 billion. With assumed average cooker lifetime of 10 years the size of the market would be 20 M units, $1.8 billion.
Solar cookers have a great potential effect not only on tropical forest conservation but also on the improvement of women's condition. Many women in developing countries collect fuelwood several hours daily. The solar cooker dissemination projects should put a major emphasis on connecting educational programs (family planning, agriculture etc.) to immediately fill the vacated collection time and social opportunities.
Solar cooker usage also promotes important health aspects. According to WHO deseases that are spread through contaminated water cause 80% of illnesses in the world . Heating water to pasteurization temperature 62.8 C destroys desease organisms . This temperature is easily achievable with solar cookers. Acute respiratory infections (ARI) are the cause of death for 1/3 of the about 15 million children under 5 years of age who die in the world each year. Large majority of these take place in the developing countries as a result of polluted indoor air due to cooking in open fire inside houses without chimney and ventilation. This problem could be greatly reduced by using the smokeless solar cookers. Solar cooker also preserves many micronutrients better (vitamins less) than pressure cooker .