Global patterns of deforestation

Irrigation for agriculture is a major cause of declining water quality in the quest for increased yield, poorly-managed irrigation systems have resulted in salinization of soils and water and sometime to land abandonment. 

Excessive use of phosphate and artificial nitrogen fertilizer, again part of the quest to increase yields, is another cause of water-quality decline. It may result in cultural eutrophication, notably a substantial increase in the nutrient content of fresh and salt water, which encourages algal growth and an eventual overall decline in biodiversity (see Section 6.3.1). The problem is widespread in coimtries where intensive industrialized crop production is prevalent and is a major problem in enclosed seas such as the Mediterranean. Industry and domestic uses of water also exact a toll. For example, in parts of the USA, Canada and Europe acid rain , caused by the burning of sulphur-rich fossil fuels, has acidified catchments and reduced water pH below the levels tolerated by most fish species algal and microbial populations have also altered. Acidification is likely to spread substantially as industrialization continues in China, India etc. The issue is discussed in Sections 5.5 and 7.7. 

Concerns about the accessibility of fresh water have led Kofi Annan, Secretary General of the United Nations, to state Global freshwater consumption rose sixfold between 1900 and 1995 - more than twice the rate of population growth. About one third of the world s population already lives in countries considered to be water stressed - that is, where consumption exceeds 10% of total supply. If present trends continue, two out of every three people on Earth will live in that condition by 2025 . The availability of clean water remains a problem in many parts of the world 20 

Global average temperature of the lowest 8 km of atmosphere has ehanged by + 0.05 0.10 °C per decade but the increase in global average surface temperature has been greater, i.e. by 0.15 0.05 °C per decade. The difference occurs mostly over tropical and sub-tropical regions.  

There have been decreases of c. 10 % in the extent and duration of lake ice cover in the mid- and high-latitudes of the northern hemisphere during the 1990s. 

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Figure 8.2 Global patterns of deforestation (based on World Bank, 2004a)...

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