Hasil untuk "Agriculture"

T. Landers, Bevin Cohen, T. Wittum et al.

C. Rosenzweig, James W. Jones, J. Hatfield et al.

M. Salleh, D. Mahmoud, Wan Azlina Wan Abdul Karim et al.

H. Gibbs, A. Ruesch, F. Achard et al.

R. DeFries, T. Rudel, M. Uriarte et al.

F. Geiger, J. Bengtsson, F. Berendse et al.

D. Sud, G. Mahajan, M. Kaur

Seline S. Meijer, D. Catacutan, O. Ajayi et al.

O. Ioannidou, A. Zabaniotou

P. Crutzen, M. Andreae

Biomass burning is widespread, especially in the tropics. It serves to clear land for shifting cultivation, to convert forests to agricultural and pastoral lands, and to remove dry vegetation in order to promote agricultural productivity and the growth of higher yield grasses. Furthermore, much agricultural waste and fuel wood is being combusted, particularly in developing countries. Biomass containing 2 to 5 petagrams of carbon is burned annually (1 petagram = 1015 grams), producing large amounts of trace gases and aerosol particles that play important roles in atmospheric chemistry and climate. Emissions of carbon monoxide and methane by biomass burning affect the oxidation efficiency of the atmosphere by reacting with hydroxyl radicals, and emissions of nitric oxide and hydrocarbons lead to high ozone concentrations in the tropics during the dry season. Large quantities of smoke particles are produced as well, and these can serve as cloud condensation nuclei. These particles may thus substantially influence cloud microphysical and optical properties, an effect that could have repercussions for the radiation budget and the hydrological cycle in the tropics. Widespread burning may also disturb biogeochemical cycles, especially that of nitrogen. About 50 percent of the nitrogen in the biomass fuel can be released as molecular nitrogen. This pyrdenitrification process causes a sizable loss of fixed nitrogen in tropical ecosystems, in the range of 10 to 20 teragrams per year (1 teragram = 1012 grams).

G. Sprague

G. Blair, R. Lefroy, L. Lisle

Clarence W. Olmstead, E. Boserup, Nicholas Kaldor

D. Bartlett, J. Clough, J. Godwin et al.

P. Lancashire, H. Bleiholder, T. Boom et al.

G. Hallett, Y. Hayami, Vernon W. Rutton

P. Williams, K. Norris

Kiminori Matsuyama

Margaret Mwangi, S. Kariuki

R. Zomer, H. Neufeldt, Jian-chu Xu et al.

Agroforestry systems and tree cover on agricultural land make an important contribution to climate change mitigation, but are not systematically accounted for in either global carbon budgets or national carbon accounting. This paper assesses the role of trees on agricultural land and their significance for carbon sequestration at a global level, along with recent change trends. Remote sensing data show that in 2010, 43% of all agricultural land globally had at least 10% tree cover and that this has increased by 2% over the previous ten years. Combining geographically and bioclimatically stratified Intergovernmental Panel on Climate Change (IPCC) Tier 1 default estimates of carbon storage with this tree cover analysis, we estimated 45.3 PgC on agricultural land globally, with trees contributing >75%. Between 2000 and 2010 tree cover increased by 3.7%, resulting in an increase of >2 PgC (or 4.6%) of biomass carbon. On average, globally, biomass carbon increased from 20.4 to 21.4 tC ha−1. Regional and country-level variation in stocks and trends were mapped and tabulated globally, and for all countries. Brazil, Indonesia, China and India had the largest increases in biomass carbon stored on agricultural land, while Argentina, Myanmar, and Sierra Leone had the largest decreases.