Overview on Agriculture and Climate Interaction

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The agricultural production system is strongly influenced by several climate factors. Therefore it passively suffers or benefits from climate change. On the other hand it actively influences climate change due to two separate aspects: During most of its production steps greenhouse gases are emitted, which adversely influences the climate. However, agriculture is the producer of renewable crops which replace fossil fuels and supply industry with renewable raw material. This contributes to heavily reduced climate impacts mostly of energy and traffic sectors. To define the net effect of agriculture on climate factors, a complex analysis is necessary.

The following figures illustrate the agricultural emissions of GHGs on a global scale: Agricultural activities accounted for 10-12 percent of total anthropogenic GHG emission in 2005, which is about 5,100 to 6,100 Mio t CO2-eq./a. The number indicates higher emissions compared to industry. In the case of the USA where nearly 540 Mio t CO2-eq. are emitted, the value is 7.4 percent of the total national greenhouse gas emissions compared to only 4.6 percent from industry (without energy sector) (2005; EPA, 2007b).

Primary greenhouse gases from agriculture are methane (CH4) and nitrous oxide (N2O). CH4 contributes 3,300 Mio t CO2-eq./a and N2O about 2,800 Mio t CO2-eq./a, which is equivalent to about 50 and 60 percent of global anthropogenic emissions by these substances, respectively.

Methane is emitted from enteric fermentation of domestic animals, especially beef and dairy cattle, which are the largest emitters of CH4 due to their ruminant digestion system. Rice cultivation is 11 percent on global average. It dominates in the group of developing countries where it accounts for more than 90 percent of the world total. Rice production emissions are of minor importance in developed countries due to lower production numbers as well as different cultivation methods. Also burning of biomass (12 percent) is mostly due to such activities in the developing rather than in the developed countries. Another 7 percent originate from the management of manure from livestock.

N2O is predominantly released by agricultural soil management activities. In the case of the USA it accounts for more than five percent of total national emissions or three-quarters of the total national N2O emissions. Other sources of N2O are manure management in animal breeding and agricultural residue burning. It is to be mentioned that in the case of residual burning CO2 emissions are not counted as climatically relevant, since the assumption is made that carbon released from biomass burning into the environment as CO2 will be reabsorbed in the following seasons. Only methane, N2O, CO and NOx, are considered in the budget of biomass burning.

How much its five main GHG sources contribute to the total of modern agriculture emissions through CH4 and N2O in the global mean as well as in a highly developed agriculture (in the case of the USA) is given in table 11.1 in relative numbers. For the USA the percentage is based on a national total of about 540 Mio t CO2-eq. in 2005 (EPA, 2007b).

Table 11.1 GHG emissions in agriculture (Global and U.S. agriculture, 2005; percent)

GHG source

U.S. agriculture (EPA, 2007b)

World

(IPPC, 2007c)

CH4

N2O

N2O and CH4

Enteric fermentation of livestock

20.9

0

32

Manure management

7.7

1.8

7

Rice cultivation

1.3

0

11

Agricultural residues burning

0.2

0.1

12

Agricultural soil management

0

68.1

38

The recent figures in non-CO2 GHG emissions are a consequence of a strong increase observed during the last two decades when the average emission increased by about 60 Mio t CO2-eq. annually (from 1990 to 2005). Nearly 90 percent were due to biomass burning, enteric fermentation and soil nitrogen emissions. A decrease was seen in the developed countries. Of future non-CO2 emissions estimates are about 8,300 Mio t CO2-eq. by 2030 (IPCC, 2007c).

As was mentioned, emissions by agriculture are the one side of the medal by which it has high climate impacts. On the other hand agriculture is highly sensitive to climate variability and weather extremes such as severe droughts, floods and storms, which are critical to farm productivity. Climate variability and change also modify the risks of fires, pest and pathogen outbreak, negatively affecting food, fiber and forestry (IPCC, 2007c). Table 11.2 connects climate change and agricultural productivity (EPA, 2007c).

Table 11.2 Effect of climate change factors on agriculture

Climate factor

Effects

Influence

Average temperature increase

Lengthen the growing season in regions with a relatively cool spring and fall

+

Adversely affect crops in regions where summer heat already limits production

-

Increase soil evaporation rates

-

Increase the chances of severe droughts

-

Change in rainfall amount and patterns

Changes in rainfall affects soil erosion rates and soil moisture

-

Precipitation will increase in high latitudes

+

Precipitation will decrease in most subtropical land regions

-

Number of extreme precipitations will increase

-

Rising atmospheric concentrations of CO2

Increasing atmospheric CO2 levels can act as a fertilizer and enhance the growth of some crops such as wheat, rice and soybeans

+

Pollution levels such as tropo-spheric ozone

Higher levels of ground level ozone limit the growth of crops

-

Change in climatic variability and extreme events

Changes in the frequency and severity of heat waves, drought, floods and hurricanes, are foreseen by global climate models

Factors given in table 11.2 must not be considered separately. Positive effects by one factor may be offset by others. While food production may benefit from a warmer climate or an elevated CO2 level, high levels in ozone concentration in atmosphere and lower precipitation may reduce yields. Moreover, regional effects must be considered which cannot be forecasted by global models. In general, after recent studies it is expected that agriculture in industrialised regions will be less vulnerable to climate change than in developing countries.

In North American rain fed agriculture the climate change will likely increase yields by 5 to 20 percent over the next decades, with high spatial variability. Special problems are foreseen in the tropics where agriculture may have little ability to adapt. In certain regions the changes in climate, water supply and soil moisture could make it less feasible to continue crop production. However, agriculture sector's ability to cope with and adapt to climate variability and change will depend not only on changing climate conditions. Adaptation through future changes in technology, management practices, in food and renewable crop demand, in water availability, and soil quality will be crucial (EPA, 2007c).

Though agricultural emissions are not more than 10 to 12 percent of world totals, mitigation in this sector is studied intensively. It concentrates on the i) reduction of emissions, ii) enhancing of removals as well as iii) avoiding or displacing of emissions (IPCC, 2007c). They have to be applied in complex. The total mitigation potential on a global scale was estimated to 4,500 to 6,000 Mio t CO2-eq. annually if there were no economic constraints. Of this numbers about 90 percent were due to soil carbon sequestration and nine and two percent by methane and nitrous oxide mitigation options, respectively. If constraints by carbon prices would be in the range up to 20 US$, a mitigation potential of about 1,500 Mio to CO2-eq. in 2030 was calculated by models.

The following chapters deal with the emission situation and the mitigation options for selected agricultural activities.

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