Cool Farming: Climate impacts of agriculture and mitigation potential.
Está a nivel de decisiones políticas realizar la transición de una agricultura “netamente productora de cambio climático” a una “netamente absorbente de gases de efecto invernadero”.
Requiere abandonar el actual modelo agrícola-ganadero.
Informe “Agricultura y cambio climático: impactos climáticos de la agricultura y potencial de mitigación” (2008), de Greenpeace señala que la agricultura tiene un elevado potencial para pasar de ser uno de los mayores productores de gases de efecto invernadero (GEI), responsables del cambio climático, a un sumidero neto de carbono, siempre que se cambie el actual modelo agrícola-ganadero.
El estudio, escrito por el equipo del profesor Pete Smith, uno de los autores de informes del IPCC (Panel Intergubernamental de Cambio Climático de la ONU), detalla las prácticas destructivas de la agricultura industrial que contribuyen al calentamiento global.
Cool Farming: Climate impacts of agriculture and mitigation potential
Jessica Bellarby, Bente Foereid, Astley Hastings and Pete Smith from the UNIVERSITY of ABERDEEN.
Un modelo agrícola basado en el respeto a la materia orgánica del suelo, en no destruir los bosques y los ecosistemas puede lograr que se pase de una agricultura “netamente productora de cambio climático a una netamente absorbente de gases de efecto invernadero”.
El informe señala que uno de los mayores problemas de la agricultura industrial es el uso masivo de fertilizantes y advierte de que más de un 50% de los mismos aplicados a los suelos se dispersa en el aire o acaba en los cursos de agua.
Uno de los GEI más potente es el óxido nitroso (N2O), con un potencial de producción de calentamiento global unas 296 veces mayor que el CO2.
Así, el empleo masivo de fertilizantes y las emisiones de N2O resultantes equivalen a 2,1 billones de toneladas de CO2 cada año, a lo que se añaden otros 410 millones procedentes de la producción de esos productos químicos (datos de 2007).
La segunda mayor fuente de emisiones agrícolas es la ganadería, ya que al digerir los alimentos los animales producen grandes cantidades de metano, un potente GEI.
A cow in Argentina has its methane emissions collected in a plastic tank. Argentine scientists say cows could be generating 30% of Argentina’s greenhouse gas emissions. Almost half of all global methane emissions comes from belching livestock, mainly cows but also pigs, goats and sheep. Methane is twenty times more potent as a greenhouse gas than carbon dioxide.
Cada kilo de cordero producido, por ejemplo, genera 17 kilos de emisiones y cada kilo de vacuno, 13 kilos, según el informe, que explica que el porcino y las aves, aunque también son grandes productoras de GEI, generan menos de la mitad de esas cifras.
El metano, el óxido nitroso y los gases industriales fluorados son también importantes gases de efecto invernadero. Las fuentes principales de emisiones de metano son la ganadería, la agricultura y la destrucción de los bosques, y pueden liberarse también enormes cantidades por la fusión del permafrost. La agricultura es también la fuente principal de óxido nitroso. Los gases fluorados industriales utilizados en refrigeración, aire acondicionado y algunos procesos químicos también contaminan la atmósfera.
Overall finding and conclusions:
Agriculture contributes significantly to greenhouse gas emissions (GHG). Agricultural soil and livestock directly emit large amounts of potent greenhouse gases. Agriculture’s indirect emissions include fossil fuel use in farm operations, the production of agrochemicals and the conversion of land to agriculture. The total global contribution of agriculture, considering all direct and indirect emissions, is between 8.5 – 16.5 Pg CO all global human-induced GHG emissions, including land use changes.
Some historic anomalies in the atmospheric GHG concentrations can be attributed to early changes in farming practices such as the development of wet rice cultivation several thousands of years ago. In the last century, there have been even more substantial changes in agriculture, with the uptake of synthetic fertilisers, development of new crop varieties (“Green Revolution”) and the adoption of large-scale farming systems. The sustainability of modern “industrial” agriculture has been questioned.
The solution to the environmental problems caused by today’s agricultural methods lies in a shift to farming practices which could provide large-scale carbon sinks, and offer options for mitigation of climate change: improved cropland management (such as avoiding bare fallow, and appropriate fertiliser use), grazing-land management, and restoration of organic soils as carbon sinks. Since meat production is inefficient in its delivery of products to the human food chain, and also produces large emissions of GHG, a reduction of meat consumption could greatly reduce agricultural GHG emissions. Taken together, these could change the position of agriculture from one of the largest greenhouse gas emitters to a much smaller GHG source or even a net carbon sink.
Footnote 1) 1 Pg (Peta gram) = 1 Gt (Giga tonne) = 1000 million tonnes. To convert Pg CO2-eq to million tonnes multiply by 1000; e.g. 15.5 Pg CO2-eq equals 15.5 Gt CO2-eq or 15500 million tonnes CO2-eq.
Footnote 2) Emissions of greenhouse gases nitrous oxide (N2O) and methane(CH4) are often expressed as the equivalent units in CO2 in terms of their global warming potential in 100 years: N2O has 296 times the warming potential of CO2 and CH4 23 times.
OVERVIEW: THE MAIN SOURCES OF GREENHOUSE GAS EMISSIONS IN AGRICULTURE
Agriculture directly contributes between 5.1 and 6.1 Pg CO2-
eq (10 – 12%) to global greenhouse gas emissions. These
emissions are mainly in the form of methane (3.3 Pg CO2-eq
yr-1) and nitrous oxide (2.8 Pg CO2-eq yr-1) whereas the net
flux of carbon dioxide is very small (0.04 Pg CO2-eq yr-1).
Nitrous oxide (N2O) emissions from soils and methane (CH4)
from enteric fermentation of cattle constitute the largest
sources, 38% and 32% of total non-CO2 emissions from
agriculture in 2005, respectively. Nitrous oxide emissions are
mainly associated with nitrogen fertilisers and manure applied
to soils. Fertilisers are often applied in excess and not fully
used by the crop plants, so that some of the surplus is lost as
N2O to the atmosphere. Biomass burning (12%), rice
production (11%), and manure management (7%) account for
Clearing of native vegetation for agriculture (i.e. land use
change rather than agriculture per se) does release large
quantities of ecosystem carbon as carbon dioxide (5.9 ± 2.9
Pg CO2-eq yr-1).
The magnitude and relative importance of the different
sources and emissions vary widely between regions. Globally,
agricultural methane (CH4) and nitrous oxide (N2O) emissions
have increased by 17% from 1990 to 2005, and are projected
to increase by another 35 – 60% by 2030 driven by growing
nitrogen fertiliser use and increased livestock production.
TABLE 1. Sources of direct and indirect agriculture greenhouse gases
Sources of agriculture Million tonnes GHG CO2-eq
Nitrous oxide from soils ——————————————–2128
Methane from cattle enteric fermentation ———————–1792
Biomass burning ——————————————————-672
Rice production ——————————————————–616
Fertiliser production ————————————————–410
Farm machinery (seeding, tilling, spraying, harvest) ————158
Pesticide production —————————————————- 72
Land conversion to agriculture ————————————-5900
AGROCHEMICALS AND CLIMATE CHANGE
In addition to the direct agriculture emissions mentioned
above, the production of agrochemicals is another important
source of greenhouse gas emissions. Especially the life cycle
of fertiliser contributes significantly to the overall impact of
industrialized agriculture. The production of fertilisers is energy
intensive, and adds a noticeable amount, between 300 and
600 million tonnes (0.3 – 0.6 Pg) CO2-eq yr-1, representing
between 0.6 – 1.2% of the world’s total GHGs. The greatest
source of GHG emissions from fertiliser production is the
energy required, which emits carbon dioxide, although nitrate
production generates even more CO2-eq in the form of nitrous
oxide. With the intensification of agriculture, the use of
fertilisers has increased from 0.011 Pg N in 1960/61, to 0.091
Pg N in 2004/2005. Application rates vary greatly between
regions with China contributing 40% and Africa 2% to global
mineral fertiliser consumption.
Compared to fertiliser production, other farm operations such
as tillage, seeding, application of agrochemicals, harvesting
are more variable across the globe with emissions between
0.06 and 0.26 Pg CO2-eq yr-1. Irrigation has average global
GHG emissions of between 0.05 and 0.68 Pg CO2-eq yr-1.
The production of pesticides is a comparatively low GHG
emitter with 0.003 to 0.14 Pg CO2-eq annually.
The amount of carbon stored in croplands is the lowest of all
land types (with the exception of deserts and semideserts).
Therefore, all land use change to cultivated land will result in a
net emission of carbon. However, the actual contribution of
land use change has a high uncertainty, but is estimated to be
5.9 ± 2.9 Pg CO2-eq. Land use change is mainly driven by
economics and legislation, but also by the availability of land.
The main expansion of global croplands is thought to be over,
though expansion into tropical forests continues to be a major
problem. Global woodland areas are projected to decrease at
an annual rate of ~43,000 km2, but developed countries are
projected to increase their woodland area by 7,400 km2
Animal farming has a wide range of different impacts, ranging
from the direct emissions of livestock, manure management,
use of agrochemicals and land use change to fossil fuel use.
Enteric fermentation contributes about 60%, the largest
amount, to global methane emissions. The demand for meat
determines the number of animals that need to be kept.
Furthermore, the livestock sector is the largest user of land,
with a shift in practice away from grazing to the growth of
livestock feed crops. The use of high energy feed crops has
recently encouraged the deforestation of the Amazon
rainforest in Brazil, a major producer of soya used in animal
feed. The demand for meat is increasing steadily, driven by
economic growth, and is likely to encourage the expansion of
intensive animal farms. The greatest increase in meat
consumption is observed in developing countries (77%
increase between 1960 and 1990), which previously had a
very low meat consumption (8% of calories from animal
sources) compared to developed countries (27% of calories
from animal sources) in 1960. Sheep and beef meat have the
highest climate impact of all types of meat, with a global
warming potential of 17 and 13 kg CO2-eq per kg of meat,
while pig and poultry have less than half of that.
Agriculture has a significant climate change mitigation
potential, which could change the position of agriculture from
the second largest emitter to a much smaller emitter or even
a net sink. There are a wide range of mitigation options in
agriculture with an overall potential of up to 6 Pg CO2-eq yr-1,
but with economic potentials of around 4 Pg CO2-eq yr-1 at
carbon prices up to 100 US$ t CO2-eq-1. This overall potential
could mitigate close to 100% of agriculture’s direct emissions.
By far the greatest mitigation contribution originates from soil
carbon sequestration (5.34 Pg CO2-eq yr-1), but also methane
(0.54 Pg CO2-eq yr-1) and nitrous oxide (0.12 Pg CO2-eq yr-1)
emissions can be considerably reduced.
The low carbon concentration in croplands means that there
is a great potential to increase carbon content through
beneficial management practices. Where land uses have
changed to become predominantly agricultural, restoration of
the carbon content in cultivated organic soils has a high perarea
potential and represents the area of greatest mitigation
potential in agriculture.
The most prominent options for mitigation in agriculture
1. Cropland management (mitigation potential up to ~1.45 Pg
CO2-eq yr-1) such as:
• Avoiding leaving land bare: Bare soil is prone to erosion
and nutrient leaching and contains less carbon than the
same field with vegetation. Important solutions are “catch”
and “cover” crops, which cover the soil in between the
actual crop or in fallow periods, respectively.
• Using an appropriate amount of nitrogen fertiliser by
avoiding applications in excess of immediate plant
requirements, by applying it at the right time, and by
placing it more precisely in the soil. Reducing the reliance
on fertilisers by adopting cropping systems such as use of
rotations with legume crops has a high mitigation potential.
• No burning of crop residues in the field.
• Reducing tillage: No-till agriculture can increase carbon in
the soil, but in industrial farming settings this maybe offset
by increasing reliance on herbicides and machinery.
However, for organic systems some preliminary study
results showed that reduced tillage without the use of
herbicides has positive benefits for carbon sequestration
in the soil.
2. Grazing land management (mitigation potential up to ~1.35
Pg CO2-eq yr-1) such as reducing grazing intensity or reducing
the frequency and intensity of fires (by active fire management).
These measures typically lead to increased tree and shrub
cover, resulting in a CO2 sink in both soil and biomass.
3. Restoration of organic soils that are drained for crop
production and restoration of degraded lands to increase
carbon sinks (combined mitigation potential ~2.0 Pg CO2-eq
yr-1): avoid drainage of wetlands, carry out erosion control,
add organic and nutrient amendments.
4. Improved water and rice management (~0.3 Pg CO2-eq yr-
1); in the off-rice season, methane emissions can be reduced
by improved water management, especially by keeping the
soil as dry as possible and avoiding waterlogging.
5. Lower but still significant mitigation is possible with setasides,
land use change (e.g., conversion of cropland to
grassland) and agro-forestry (~0.05 Pg CO2-eq yr-1); as well
as improved livestock and manure management (~0.25 Pg
6. Increasing efficiency in the manufacturing of fertilisers can
contribute significantly with a reduction of up to about ~0.2 Pg
CO2-eq yr-1. Improvements would be related to greater energy
efficiency in ammonia production plants (29%), introduction of
new nitrous oxide reduction technology (32%) and other
general energy-saving measures in manufacturing (39%).
7. Consumers can play an important role in the reduction of
agricultural GHG emissions. A reduction in the demand for
meat could reduce related GHG emissions considerably.
Adopting a vegetarian diet, or at least reducing the quantity of
meat products in the diet, would have beneficial GHG impacts.
A person with an average US diet for example, could save 385
kcal (equating to 95 – 126 g CO2) of fossil fuel per day by
replacing 5% of meat in the diet with vegetarian products.
report Cool Farming details the destructive practices …