Agriculture Reference
In-Depth Information
may attenuate the expected rise in GHG
emissions.
Intensive production of beef, poultry, and pork
is increasingly common, leading to increases in
manure with consequent increases in GHG emis-
sions. This is particularly true in the developing
regions of South and East Asia, and Latin
America, as well as in North America.
Changes in policies (e.g., subsidies) and
regional patterns of production and demand are
causing an increase in international trade of agri-
cultural products. This is expected to increase
CO
2
emissions, due to greater use of energy for
transportation.
an area. For example, if rainforest is removed and
replaced by crops, there will be less transpiration
(evaporation of water from leaves) leading to
warmer temperatures in that area. On the other
hand, if irrigation is used on farmland, more
water is transpired and evaporated from moist
soils, which cools and moistens the atmosphere.
The additional transpiration can also affect levels
of precipitation and cloudiness in an area.
In regions with heavy snowfall, reforestation
or afforestation would cause the land to refl ect
less sunlight, resulting in the absorption of more
heat on the land. This would, in turn, result in a
net warming effect despite the removal of carbon
dioxide from the atmosphere through the process
of photosynthesis during the growing season.
Additional reforestation could increase transpira-
tion, leading to more water vapor in the air. In the
troposphere, water vapor is considered to be the
biggest greenhouse gas contributor to global
warming.
3.2.1
Land Use Change
Land use and land-use changes can signifi cantly
contribute to overall climate change. Vegetation
and soils typically act as a carbon sink, storing
carbon dioxide that is absorbed through photo-
synthesis. When the land is disturbed, the stored
carbon dioxide along with methane and nitrous
oxide are emitted, reentering the atmosphere.
The clearing of land can result in soil degrada-
tion, erosion, and the leaching of nutrients, which
can also possibly reduce its ability to act as a car-
bon sink. This reduction in the ability to store
carbon can result in additional carbon dioxide
remaining in the atmosphere, thereby increasing
the total amount of greenhouse gases.
There are two types of land-use change: direct
anthropogenic (human-caused) changes and indi-
rect changes. Examples of anthropogenic changes
include deforestation, reforestation and afforesta-
tion, and agriculture. Indirect changes include
those changes in climate or in carbon dioxide
concentrations that force changes in vegetation.
On a global scale, carbon dioxide emissions from
land-use changes represent an estimated 18 % of
total annual emissions; one-third of that from
developing countries and over 60 % from the
lesser developing countries.
3.2.1.2 Indirect Changes
The main ways that changes in climate can alter
land use is through higher mean annual tempera-
tures, altered precipitation patterns, and more fre-
quent and extreme weather events. The territories
of many plant species depend largely on tempera-
ture and rainfall patterns. As climate change
affects these patterns, many types of trees and
vegetation are forced to shift to higher altitudes
and latitudes. While greater variability in rainfall
patterns can decrease overall plant growth, higher
temperatures can extend growing seasons, possi-
bly allowing for more than one cropping cycle
during the same season or the expansion of agri-
cultural land toward the higher elevations.
3.2.2
Agricultural Soils (N
2
O)
N
2
O is produced naturally in soils through the
microbial process of denitrifi cation and nitrifi ca-
tion. A number of anthropogenic activities add
nitrogen to the soils, thereby increasing the
amount of nitrogen available for nitrifi cation and
denitrifi cation and ultimately the amount of N
2
O
emitted (US-EPA
2011
).
3.2.1.1 Direct Anthropogenic Changes
The effect of land use on the climate primarily
depends on the type of land cover present within
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