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freshwater ecosystems are currently declining faster than marine or land
ecosystems making them the world's most vulnerable habitats. Increasing
urbanization pollutes clean water supplies and much of the world still does
not have access to clean, safe water. In the industrial world demand
management has slowed absolute usage rates but increasingly water is being
transported over vast distances from water-rich natural areas to population-
dense urban areas and energy-hungry desalination is becoming more widely
used. Greater emphasis is now being placed on the improved management of
blue (harvestable) and green (soil water available for plant use) water, and
this applies at all scales of water management.
Forests
Present-day forests occupy about a quarter of the world’s ice-free land
with about half of these occurring in the tropics. In temperate and boreal
regions forest area is gradually increasing (with the exception of Siberia), but
deforestation in the tropics is of major concern.
Forests moderate the local climate and the global water cycle through
their light reflectance and evapotranspiration. They also conserve
biodiversity, protect water quality, preserve soil and soil quality, provide fuel
and pharmaceuticals, and purify the air. These free ecosystem services are
not given a market value under most current economic systems, and so forest
conservation has little appeal when compared with the economic benefits of
logging and clearance which, through soil degradation and organic
decomposition returns carbon dioxide to the atmosphere. The United Nations
Food and Agriculture Organization (FAO) estimates that about 90% of the
carbon stored in land vegetation is locked up in trees and that they sequester
about 50% more carbon than is present in the atmosphere. Changes in land
use currently contribute about 20% of total global carbon emissions. Climate
change can be mitigated by sequestering carbon in reafforestation schemes,
plantations and timber products. Also wood biomass can be utilized as a
renewable carbon-neutral fuel. The FAO has suggested that, over the period
2005–2050, effective use of tree planting could absorb about 10–20% of
man-made emissions – so monitoring the condition of the world's forests
must be part of a global strategy to mitigate emissions and protect ecosystem
services.
Cultivated land
Rice, wheat, corn and potatoes make up more than half the world's food
supply.
Feeding more than six billion human bodies takes a heavy toll on the
Earth’s resources. This begins with the appropriation of about 38% of the
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