Agriculture Reference
In-Depth Information
16.1 INTRODUCTION
Climate change is perceived to be the greatest threat to the food security
and mankind in twenty-first century. Over the past few decades, increase
in average air temperature on earth and its associated effects on climate
and crops have became a concern worldwide, particularly after the 4th As-
sessment Report of Intergovernmental Panel on Climate Change (IPCC,
2007). Since preindustrial era to the year 2009, the carbon dioxide (CO
2
)
concentration in the atmosphere has increased from 280 ppm to 384 ppm
coupled with an increase in mean temperature of 0.76ºC. Further, accord-
ing to the studies carried out by IPCC, it is predicted that by the end of
this century increase in average air temperature in Asian countries could
range between 1.8 to 6.0ºC and CO
2
concentration may reach up to 700
ppm or more (IPCC, 2007). South Asian countries are predicted to have
least increase in temperature, in the range of 1.8 to 5.0ºC except for the
Himalayas (IPCC, 2007). On the other hand, changes in rainfall pattern
have also been predicted in the range of 5 to 20% during the winter season
and 40 to 15% during the summer season (IPCC, 2007). As a consequence
of rising atmospheric temperature, there will be frequent occurrence of
drought, flood and heat waves.
Temperature increase and the effects of greenhouse gases are among
the most important issues associated with climate change. The major
greenhouse gasses (GHGs) responsible for climate change are carbon di-
oxide (CO
2
), methane (CH
4
) and nitrous oxide (N
2
O). Collectively, these
three gasses are responsible for 99% of global warming. Moreover, perflu-
orocarbons (PFCs), hydroflourocarbons (HFCs), sulfur hexafluoride (SF
6
)
and ozone (O
3
) also make a small contribution to global warming. Among
the different GHGs, carbon dioxide is the most important GHG and is
alone responsible for 77% of global warming. The global warming poten-
tial of different GHGs is measured in terms of carbon dioxide equivalence
(CO
2eq
), which is the warming effect exerted by one molecule of CO
2
over
a given period of time, usually 20 or 100 years. Methane and nitrous oxide
have a global warming potential over a 100 year period are about 23 CO
2eq
and 298 CO
2eq
, respectively.
