Transcript PPT - University of Saskatchewan

Methane: the issue, the
Science, the Solution
Roger Cohen
Department of Animal & Poultry Science
University of Saskatchewan
Focus on beef cattle
•Rifkin (1992) - Beyond beef: The rise and fall of
the cattle culture
“Cattle production and beef consumption now
rank among the gravest threats to the future
well-being of the earth and its human
population”
• Ryan Eliason (undated) - YES Handbook
“Cattle and other livestock account for twice
the amount of pollutants as come from all
U.S. industrial sources”
“Livestock production is perhaps the most
massive force behind the destruction of our
planet”
The earth’s climate is changing
 Significant changes during 20th century
• The cause is the enormous increase in
anthropomorphic emission of greenhouse
gases (GHG)
•Carbon dioxide
•Nitrous oxide
•Methane
Carbon dioxide
 Important sources are:
- Burning of fossil fuels (coal & petroleum)
- clearing and burning forests for crop
and livestock production
Nitrous oxide
• Important sources are:
- Application of nitrogen fertilizer
- Soil disturbance
• Crop production most responsible
Alleviated by
- Deep banding
- Zero till
• Little use on pasture - legumes preferred
Methane
• By-product of anaerobic decomposition
of organic matter
•Important Non-anthropomorphic sources:
- wetlands
- Forest fires
• Important agricultural sources:
Rice farming
Ruminant livestock
Manure (all species)
• Other anthropomorphic sources:
- Human waste
Landfills, sewage, waste water
- Fossil fuel industry
Natural gas, petroleum processing,
coal mining
Global Warming Potential of GHG
CO2
Radiative forcing relative to CO2
Lifetime (years)
GWP in 100 years relative to CO2
CH4
N2O
1
58
206
120
10
150
1
21
290
Global Emissions (Gt/yr) a
21.9
0.5
0.021
Global Emissions (GWP) b
21.9
10.5
6.1
a
1 Gt = 1 billion tonnes
b
Potential for a unit of gas for warming the world
1.14%
0.98%
2.89%
2.25%
3.38%
6.59%
Wetlands
Humans
Forest fires
Cattle
82.77%
Manure
Natural gas leaks
Other
Figure 1. Sources of methane in Canada as a percent of the total methane emission
Sources of methane in Canada as a
percentage of total methane emissions
Cattle
Humans
16.8%
Forest fires
Cattle
Wild animals
Forest fires
Other domestic animals
19.6%
Humans
Manure
38.3%
Natural gas leaks
Fuel combustion
Coal mining
Other industry
Biomass
Sources of methane in Canada excluding
wetlands
 Domestic livestock account for about 30% of
anthropomorphic methane emissions in North
America. Main sources are:
• Eructated gas from ruminants (Cattle & sheep)
• Manure
 Are cattle a major cause of climate warming
or can they be part of the solution?
Recycling carbon through plants
and animals is an important part of
the solution to the GHG problem
• CO2 taken up by plants and stored in leaves,
stems and roots as carbohydrates (cellulose,
hemicellulose,lignin)
• Cattle eat leaves and stems and return 25-60%
of the Carbon to soil in feces
• Incorporated into soil organic matter which
enhances physical & chemical characteristics
of the soil encouraging further plant growth
• Most important role in recycling carbon
belongs to the roots because they carry the
carbon directly into the soil
 Two categories of plants
used in agriculture
• Perennial grasses and legumes used for
ruminant livestock feed (73% of beef
cattle feed)
• Annual plants (cereal, oilseed & pulse
crops etc.)
Perennial plants
• Deep extensive root system
• Dry matter below ground (roots carbon) =
DM above ground (leaves + stems carbon)
• About 50% of roots die and regenerate each
year burying carbon deep in the soil
• Channels from decayed roots improve
moisture penetration and plant growth
• Proper defoliation (grazing or mechanical)
stimulates new growth of leaves, stems, roots
• Incorrect defoliation (severe, wrong time) will
weaken the plant which will eventually disappear
• Careful management of defoliation is therefore
critical to the mitigation of climate change
Annual plants
• Shallow roots
• Above ground carbon >> below ground
• Much of the carbon is removed from the
system in the harvested material (grain)
• Net depletion of soil organic matter
(carbon) over time
 Carbon sequestration
enhanced by:
• Replacing degraded crop land with
permanent pasture
• Incorporating perennial forages (pasture/hay)
into crop rotations
Benefits other than removal of
atmospheric carbon include:
• Reduced land degradation from wind and
water erosion
• Increased soil organic matter, fertility &
water holding capacity
• Soil salinity is checked
• Deep water penetration is increased
It is the relative inefficiency of
producing beef from pasture that
makes it the most sustainable
form of agricultural production
What about the methane
emitted by cattle?
• The carbon in this source of methane is
not “new” carbon - it is recycled carbon
• Methane emitted by the coal and
petroleum industries is “new” carbon
60 million bison roamed the northern
great plains before settlement
Today there are only about 32 million
cattle in the northern great plains region
Carbon balance in a mixed native
grass pasture grazed by 1 cow and
calf on 2 ha (5 ac)
 CARBON SINKS:
• Atmospheric CO2 taken up by pasture
• Atmospheric CH4 absorbed by soil
• Manure C incorporated into soil
• C in pasture eaten by cow and calf
• C passed from cow to calf in milk
• C retained by calf as growth
 CARBON SOURCES:
• Respired CO2 from cow and calf
• Eructated CO2 from cow and calf
• Eructated CH4 from cow and calf
• CH4 from manure of cow and calf
• CO2 from manure of cow and calf
• CH4 from decomposition of plant matter
 Total carbon sinks = 20.73 kg C / d
 Total carbon sources = 2.99 kg C / d
GWP of CO2 and CH4 = 1 and 21
Removal of GWP gases by cow & calf
= 20.65 units / d
Emission of GWP gases by cow & calf
= 6.46 unit / d
Net reduction in GWP = 14.19 units / d
In a single grazing season of 150
days this is a REMOVAL of
2,127.9 units of GWP gases
from the atmosphere
Assuming that the cow & calf emit a similar
amount of CO2 and CH4 to the atmosphere for
the remaining 215 days of the year and that
there is no removal of CO2 and CH4 from the
atmosphere by pasture and soil during winter:
Total sources of GWP gases = 2,359 units / year
Total sinks of GWP gases
=
3,098 units / year
Net removal of GWP gases = 739 units / year
 CONCLUSION
Grazing beef cattle are an integral
part of climate change mitigation
Policy recommendations
• Support for grazing management research &
extension
• Encourage correct management of all pasture
lands through research and extension
• Encourage return degraded crop land to
permanent pasture
• Encourage integration of perennial forage into
cropping practices
• Encourage more backgrounding and finishing of cattl
on pasture