Inexhaustible resources and environmental problems

Agro-climatic resources are the possibilities of the climate for farming; they are set mainly by the sum of effective temperatures above +10 °C and by the moisture coefficient (precipitation divided by possible evaporation). Around the equator there is a lot of heat, so two or three harvests a year are possible, while near the poles farming is hard. Among land resources, arable land is the most valuable: although it covers only about a tenth of the world land fund, it gives most of the food, while pastures cover about a quarter. Erosion, salinisation, waterlogging and city growth are reducing land. Fresh water is only 2.5 % of the hydrosphere and much of it is in glaciers; rivers are the main source, with water abundant in Brazil, Russia, Canada, the USA and Indonesia but scarce in dry regions. Biological resources rest mainly on forests, which cover nearly a third of the land: coniferous taiga in the north (Russia, Canada) and broad-leaved forests in the tropics (Brazil, DR Congo, Indonesia). Geothermal energy is used in tectonically active areas – Iceland, Japan, New Zealand, the Philippines, Italy, Mexico and the western USA.