Tài liệu LIVESTOCK''''S ROLE IN CLIMATE CHANGE AND AIR POLLUTION ppt
03 Livestock’s role in climate change and air pollution 3.1 Issues and trends The atmosphere is fundamental to life on earth. Besides providing the air we breathe it regulates temperature, distributes water, it is a part of key processes such as the carbon, nitrogen and oxygen cycles, and it protects life from harmful radiation. These functions are orchestrated, in a fragile dynamic equilibrium, by a complex phys- ics and chemistry. There is increasing evidence that human activity is altering the mechanisms of the atmosphere. In the following sections, we will focus on the anthropogenic processes of climate change and air pollution and the role of livestock in those processes (excluding the ozone hole). The con- tribution of the livestock sector as a whole to these processes is not well known. At virtually each step of the livestock production process substances contributing to climate change or air
pollution, are emitted into the atmosphere, or their sequestration in other reservoirs is ham- pered. Such changes are either the direct effect of livestock rearing, or indirect contributions from other steps on the long road that ends with the marketed animal product. We will analyse the most important processes in their order in the food chain, concluding with an assessment of their cumulative effect. Subsequently a num- ber of options are presented for mitigating the impacts. 80 Livestock’s long shadow Climate change: trends and prospects Anthropogenic climate change has recently become a well established fact and the result- ing impact on the environment is already being observed. The greenhouse effect is a key mech- anism of temperature regulation. Without it, the average temperature of the earth’s surface would not be 15ºC but -6ºC. The earth returns energy received from the sun back to space by reflection of light and by emission of heat. A part of the heat flow is absorbed by so-called green- house gases, trapping it in the atmosphere. The principal greenhouse gases involved in this process include carbon dioxide (CO 2 ), methane (CH 4 ) nitrous oxide (N 2 O) and chlorofluorocar- bons. Since the beginning of the industrial period anthropogenic emissions have led to an increase in concentrations of these gases in the atmo- sphere, resulting in global warming. The average temperature of the earth’s surface has risen by 0.6 degrees Celsius since the late 1800s.