Features Fruit Production
High-yield ag slows global warming: researchers

June 16, 2010 – Advances
in high-yield agriculture over the latter part of the 20th century have
prevented massive amounts of greenhouse gases from entering the atmosphere –
the equivalent of 590 billion metric tons of carbon dioxide – according to a
new study led by two Stanford University scientists.

June 16, 2010 – Advances
in high-yield agriculture over the latter part of the 20th century have
prevented massive amounts of greenhouse gases from entering the atmosphere –
the equivalent of 590 billion metric tons of carbon dioxide – according to a
new study led by two Stanford University scientists.

The researchers estimate
that if not for increased yields, additional greenhouse gas emissions from
clearing land for farming would have been equal to as much as a third of the
world’s total output of greenhouse gases since the dawn of the Industrial
Revolution in 1850.

The researchers also
calculated that for every dollar spent on agricultural research and development
since 1961, emissions of the three principal greenhouse gases – methane,
nitrous oxide and carbon dioxide – were reduced by the equivalent of about a
quarter of a ton of carbon dioxide – a high rate of financial return compared
to other approaches to reducing the gases.

“Our results dispel the notion
that modern intensive agriculture is inherently worse for the environment than
a more ‘old-fashioned’ way of doing things,” said Jennifer Burney, lead author
of a paper describing the study that is published online by the Proceedings of
the National Academy of Sciences.

The researchers calculated
emissions of carbon dioxide, methane and nitrous oxide, converting the amounts
of the latter two gases into the quantities of carbon dioxide that would have
an equivalent impact on the atmosphere, to facilitate comparison of total
greenhouse gas outputs.

Burney, a postdoctoral
researcher with the Program on Food Security and the Environment at Stanford,
said agriculture currently accounts for about 12 per cent of human-caused
greenhouse gas emissions. Although greenhouse gas emissions from the production
and use of fertilizer have increased with agricultural intensification, those
emissions are far outstripped by the emissions that would have been generated
in converting additional forest and grassland to farmland.

“Every time forest or
shrub land is cleared for farming, the carbon that was tied up in the biomass
is released and rapidly makes its way into the atmosphere – usually by being
burned,” she said. “Yield intensification has lessened the pressure to clear
land and reduced emissions by up to 13 billion tons of carbon dioxide a year.”

“When we look at the costs
of the research and development that went into these improvements, we find that
funding agricultural research ranks among the cheapest ways to prevent
greenhouse gas emissions,” said Steven Davis, a co-author of the paper and a
postdoctoral researcher at the Carnegie Institution at Stanford.

To evaluate the impact of
yield intensification on climate change, the researchers compared actual agricultural
production between 1961 and 2005 with hypothetical scenarios in which the
world's increasing food needs were met by expanding the amount of farmland
rather than by the boost in yields produced by the Green Revolution.

“Even without higher
yields, population and food demand would likely have climbed to levels close to
what they are today,” said David Lobell, also a coauthor and assistant
professor of environmental Earth system science at Stanford.

“Lower yields per acre
would likely have meant more starvation and death, but the population would
still have increased because of much higher birth rates,” he said. “People tend
to have more children when survival of those children is less certain.”

The researchers found that
without the advances in high-yield agriculture, several billion additional
acres of cropland would have been needed.

Comparing emissions in the
theoretical scenarios with real-world emissions from 1961 to 2005, the
researchers estimated that the actual improvements in crop yields probably kept
greenhouse gas emissions equivalent to at least 317 billion tons of carbon
dioxide out of the atmosphere, and perhaps as much as 590 billion tons.

Without the emission
reductions from yield improvements, the total amount of greenhouse gas pumped
into the atmosphere over the preceding 155 years would have been between 18 and
34 per cent greater than it has been, they said.

To calculate how much
money was spent on research for each ton of avoided emissions, the researchers
calculated the total amount of agricultural research funding related to yield
improvements since 1961 through 2005. That produced a price between
approximately $4 and $7.50 for each ton of carbon dioxide that was not emitted.

“The size and
cost-effectiveness of this carbon reduction is striking when compared with
proposed mitigation options in other sectors,” said Lobell. “For example,
strategies proposed to reduce emissions related to construction would cut
emissions by a little less than half the amount that we estimate has been
achieved by yield improvements and would cost close to $20 per ton.”

The authors also note that
raising yields alone won’t guarantee lower emissions from land use change.

“It has been shown in
several contexts that yield gains alone do not necessarily stop expansion of
cropland,” Lobell said. “That suggests that intensification must be coupled
with conservation and development efforts.

“In certain cases, when
yields go up in an area, it increases the profitability of farming there and
gives people more incentive to expand their farm. But in general, high yields
keep prices low, which reduces the incentive to expand.”

The researchers concluded
that improvement of crop yields should be prominent among a portfolio of
strategies to reduce global greenhouse gases emissions.

“The striking thing is
that all of these climate benefits were not the explicit intention of
historical investments in agriculture. This was simply a side benefit of
efforts to feed the world,” Burney noted. “If climate policy intentionally
rewarded these kinds of efforts, that could make an even bigger difference. The
question going forward is how climate policy might be designed to achieve
that.”