|
|
|
BY
LAURA REYNOLDS | MAY 8, 2013
|
|
In 2010, global
greenhouse gas emissions from the agricultural sector totaled 4.7 billion
tons of carbon dioxide (CO₂)
equivalent, up 13 percent over 1990. Agriculture is the third largest
contributor to global emissions by sector, following the burning of fossil fuels
for power and heat, and transportation. In 2010, emissions from electricity
and heat production reached 12.5 billion tons, and emissions from transport
totaled 6.7 billion tons.
Despite
their continuing rise, emissions from agriculture are growing at a much
slower rate than the sector as a whole, demonstrating the increasing carbon
efficiency of agriculture. From 1990 to 2010, the volume of agricultural
production overall increased nearly 23 percent, according to data compiled by
the United Nations Food and Agriculture Organization (FAO) for its program,
FAOSTAT. FAO released a new Greenhouse Gas Emissions database for
agriculture, forestry and other land use changes in December 2012, which can
be found here.
According to FAO, methane
accounts for just under half of total agricultural emissions, nitrous oxide
for 36 percent, and carbon dioxide for some 14 percent. The largest source of
methane emissions is enteric fermentation, or the digestion of organic
materials by livestock, predominantly beef cattle. This is also the largest
source of agricultural emissions overall, contributing 37 percent of the
total.
Livestock contribute to
global emissions in other ways as well. Manure deposited and left on pastures
is a major source of nitrous oxide emissions because of its high nitrogen
content. When more nitrogen is added to soil than is needed, bacteria convert
the extra nitrogen into nitrous oxide and release it into the atmosphere.
Emissions from manure on pasture in Asia, Africa, and South America together
account for as much as 81 percent of global emissions from this source. These
emissions from the three regions increased 42 percent on average between 1990
and 2010, reflecting an increase in range-based livestock populations;
elsewhere, these emissions either decreased or stagnated.
Carbon dioxide emissions
from cultivated organic soils account for some 14 percent of total
agricultural emissions, with Asia contributing 54 percent of these emissions.
Deforestation and clearing for agricultural land in many tropical South and
Southeast Asian countries are a leading cause of these emissions. Asia is
home to four out of the top five countries with the highest
CO2 emissions from cultivated organic soils, with Indonesia contributing
279 million tons, Papua New Guinea 41 million tons, Malaysia 35 million tons,
and Bangladesh 31 million tons.
These data clearly
indicate that livestock production accounts for an enormous share of global
greenhouse gas emissions. Together, emissions from enteric fermentation,
manure left on pastures, manure applied to soils, cropland devoted to feed
production, and manure treated in management systems contribute more than 80
percent of total emissions. Meanwhile, emissions related to the direct human
consumption of food crops represent less than 20 percent of the total.
One obvious way to reduce
agricultural emissions is for people to minimize their consumption of meat
and dairy products. This would help stabilize or shrink livestock
populations, lessen the pressure to clear additional land for livestock, and
reduce the proportion of grain that is grown for livestock feed instead of
for direct human consumption.
Farmers and landowners
have numerous opportunities to mitigate these impacts as well, bringing
environmental and even economic co-benefits. For example, applying fertilizer
more efficiently, precisely, and at times when plants can absorb it can
significantly reduce nitrous oxide emissions while lowering fertilizer costs.
Planting fallow fields with nitrogen-fixing legume crops—such as soybeans,
alfalfa, and clover—can also naturally rebuild nitrogen and other nutrients
in soils.
Growing
trees and woody perennials on land can sequester carbon while simultaneously
helping to restore soils, reduce water contamination, and provide beneficial
wildlife habitat. Reducing soil tillage can also rebuild soils while lowering
greenhouse gas emissions. Some practices can even result in increased income
for farmers: “cap-and-trade” programs allow farmers to monetize and sell
certain sequestration practices, while government programs like the U.S.
Conservation Reserve Program pay farmers to set aside some of their land for
long-term restoration. As detailed in the 2012 Worldwatch report, Innovations in Sustainable Agriculture: Supporting
Climate-Friendly Food Production, many mitigation practices use
existing and accessible technologies and can be implemented immediately.
Read
the full report at Vital Signs Online.
Laura Reynolds is a Food and Agriculture Staff
Researcher at the Worldwatch Institute
|
Social Plugin