<P> Land degradation is a process in which the value of the biophysical environment is affected by a combination of human - induced processes acting upon the land . It is viewed as any change or disturbance to the land perceived to be deleterious or undesirable . Natural hazards are excluded as a cause; however human activities can indirectly affect phenomena such as floods and bush fires . </P> <P> This is considered to be an important topic of the 21st century due to the implications land degradation has upon agronomic productivity, the environment, and its effects on food security . It is estimated that up to 40% of the world's agricultural land is seriously degraded . </P> <P> Of particular concern is N O, which has an average atmospheric lifetime of 114--120 years, and is 300 times more effective than CO as a greenhouse gas . NO produced by industrial processes, automobiles and agricultural fertilization and NH emitted from soils (i.e., as an additional byproduct of nitrification) and livestock operations are transported to downwind ecosystems, influencing N cycling and nutrient losses . Six major effects of NO and NH emissions have been identified: </P> <Ol> <Li> decreased atmospheric visibility due to ammonium aerosols (fine particulate matter (PM)) </Li> <Li> elevated ozone concentrations </Li> <Li> ozone and PM affects human health (e.g. respiratory diseases, cancer) </Li> <Li> increases in radiative forcing and global climate change </Li> <Li> decreased agricultural productivity due to ozone deposition </Li> <Li> ecosystem acidification and eutrophication . </Li> </Ol>

A study of development and it's impact on the local environment