Deforestation global

Introduction The Global Extent of Deforestation and Biomass Burning... 

Accurate estimates of deforestation on a global scale are largely unavailable, if not impossible, to ascertain. Since preagricultural times, temperate... 

Fig. 11 -25 Release of carbon from the biota and soils globally according to various estimates. The fossil fuel flux is from data of Rotty. (Modified with permission from G. M. Woodwell et al. (1983). Global deforestation Contribution to atmospheric carbon dioxide. Science 222,1081-1086, AAAS.)...

How have agriculture and deforestation changed the global rates of nitrogen fixation and denitrification How can increased agricultural productivity be sustained without using industrially produced fertilizers ... 

What has changed in the last few hundred years is the additional release of carbon dioxide by human activities. Fossil fuels burned to run cars and trucks, heat homes and businesses, and power factories are responsible for about 98% of carbon dioxide emissions, 24% of methane emissions, and 18% of nitrous oxide emissions. Increased agriculture, deforestation, landfills, industrial production, and mining also contribute a significant share of emissions (5). For example, in 1997, the United States emitted about one-fifth of total global greenhouse gases. 

Globally, it is estimated that there is 3870 million ha of forests (30 % of the Earth s land area), of which 95 % is natural or semi-natural (Table 1.1). At the present time, in most developed countries, the forest area is increasing and this is likely to continue given the present rates of harvesting. However, in tropical parts of the world, the forest area continues to decline, giving rise to serious concerns. It is estimated that between 1990 and 2000, there was a loss of 9.4 million ha per annum of forest worldwide (an annual deforestation rate of 14.6 million ha and an increase in forest area of 5.2 million ha per year Table 1.2). The only way to reverse this trend is to place sufficient economic value on forest resources, with incentives to encourage sustainable forest management. 

Climate changes from the time ofthe disappearance of dinosaurs to our days have also been based up on deep-sea stable isotope data oxygen isotope data provide an insight into the temperature variations, while carbon isotope data are informative on the kind of global carbon cycle perturbation (Zachos 2001). These data suggest that the present conditions of temperature are similar to the late Middle Age. However, the trend toward higher temperatures is now more difficult to contrast because of the drastic deforestation and emission of gases. 

With less than 5 percent of the worlds population, the United States ranks first in carbon dioxide emissions and is responsible for about 25 percent of global carbon dioxide emissions. Industrial nations worldwide are responsible for about 58 percent of carbon dioxide emissions, primarily from the combustion of fossil fuels. Developing nations account for the remaining 42 percent, but their sources of carbon dioxide are split between fossil fuels (19 percent) and deforestation (23 percent). 

---