Agricultural Research Combats Global Warming

AgMRC Renewable Energy & Climate Change Newsletter
September 2010

Don HofstrandDon Hofstrand
Professor Emeritus
Iowa State University

Global agriculture has been identified as a significant emitter of greenhouse gases.   In 2005, agriculture accounted for an estimated 10-12% of total global anthropogenic greenhouse gas emissions (emissions caused by human activity).   Although carbon dioxide (CO2) is a major contributor, agriculture also emits significant amounts of methane (CH4) and nitrous oxide (N2O).

Because commercial agriculture is an energy intensive industry, it has come under criticism for significant amounts of greenhouse gas emissions.  Much of this criticism has focused on the increased use of commercial fertilizers and other yield enhancing technologies.  However, a new study from (Stanford University) sheds new light on the topic.  It provides evidence that agricultural research focused on increasing yields has actually reduced greenhouse gas emissions from what they would have been had yields not increased.

The demand for food has increased due to the world’s growing population and higher per capita incomes. World population increased from 3.08 billion in 1961 to 6.51 billion in 2005, a 111 percent increase.  However, during this same period, crop output increased from 1.8 to 4.8 billion metric tons (metric ton = 2,205 pounds) for a 162 percent increase.   So, crop output per person increased by about 26 percent.  This has lead to the bountiful and wide variety of foods enjoyed by much of the world’s population. 

The increase in yields resulted from a variety of factors including better crop genetics, improved mechanization and irrigation and increased use and effectiveness of pesticides and other chemicals.  Although many of these factors lead to increased greenhouse gas emissions, they provide for the food needs of an expanding world population while not greatly expanding the world’s cropland area. 

If yields had not increased over this time period, the world’s food needs would have been met by greatly expanding the world’s agricultural land area.  This would have resulted in the conversion of large areas of grasslands and forests to agricultural production that would have resulted in the released of large amounts of greenhouse gases. 

To assess the comparative impact on greenhouse gas emissions between intensive agriculture production (increased yields) and extensive agriculture production (increased land area), the Stanford authors created two scenarios (Alternative 1 and Alternative 2) of extensive agriculture and compared them to the intensive system (Real World) that actually unfolded over the period from 1961 to 2005.

Real World

As shown in Table 1, there were 2,372 million acres of cropland in the world in 1961.  During the last half of the twentieth century, the cropland area grew to 2,985 million acres, an increase of 27 percent.   However, yield per acre more than doubled during this period from .74 of a metric ton per acre to 1.60 metric tons per acre.  So the great majority of the crop production increase was due to intensive expansion (yields increase) rather than extensive expansion (land area increase).

An indication of agricultural intensification is shown by the increased use of fertilizer during this period.  To achieve the yield increase, the rate of fertilizer application increased from 28.6 pounds per acre to 121 pounds per acre, an increase of 323 percent.  Total fertilizer use increased from 31 to 165 million metric tons, an increase of 432 percent, reflecting the 323 percent increase in the fertilizer application rate and the 27 percent increase in cropland area.

Alternative 1

In Alternative 1, yield levels are held constant and the world’s food needs are met entirely by cropland area expansion. In other words, if crop yields don’t increase, what level of cropland expansion is needed to provide the same amount of agricultural production that actually occurred (Real World)? 

Table 1.  Comparison of the Impact of Intensive Agriculture (increased yields) to Extensive Agriculture (increased land area).

  1961 Real World Alternative 1 Alternative 2
Cropland Area        
    Area (mil. acres) 2,372 2,985 6,723 5,115
    Change (percent)   27% 178% 110%
    Yield (metric tons per acre) .74 1.60 .74 .74
    Change (percent)   116% 0% 0%
    Rate (lbs./acre) 28.6 121 28.6 28.6
    Change (percent)   323% 0% 0%
    Total (million metric tons) 31 165 88 67
    Change (percent)   432% 183% 116%

The land area in Alternative 1 would expand to a total of 6,723 million acres.  An expansion of this size is about 20 times larger than the combined current corn and soybean acreage in the U.S.   Although the fertilization rate per acre under this scenario does not change, the total amount of fertilizer used expands by 183 percent due to the increase in acreage.

The estimated emissions from converting grassland and forests to cropland are assumed to be 42 metric tons per acre.  When used to calculate the emissions from land expansion in Alternative 1, the emissions from land expansion (Alternative 1) are much greater than the emissions from increasing yields, even after adjusting for the difference in fertilizer and other yield increasing emissions. 

Table 2. Agriculture’s Emissions by Alternative (billion metric tons carbon). 

Total Actual Anthropogenic Emissions (1850 - 2005) 478
Alternative 1 (1961 - 2005)  
    Total Emissions 639
    Change in Emissions 161
    Change as Percent of Actual Anthropogenic Emissions 34%
Alternative 2 (1961 - 2005)  
    Total Emissions 564.5
    Change in Emissions 86.5
    Change as Percent of Actual Anthropogenic Emissions 18%

Total actual anthropogenic (man-made) emissions from 1850 to 2005 are estimated to be 478 billion metric tons of carbon as shown in Table 2.  If agriculture production would have been achieved solely through land expansion (Alternative 1), emissions would have been 639 billion metric tons of carbon.  The avoided emissions from yield increases (Real World) versus land expansion (Alternative 1) are estimated to be 161 billion metric tons. So, compared to Alternative 1, yield gains achieved since 1961 have avoided an amount equal to 34 percent of the total actual emissions.   

Alternative 2

A more conservative scenario is created in the second alternative.  The world standard of living does not expand over the time period but is held constant at the 1961 level.  So food consumption per person stays the same and total food demand increases only due to increased population.  As in Alternative 1, yield is assumed to stay constant at the 1961 level with the increased food supply coming from expanded acres.     

As expected, the acreage expansion in Alternative 2 is less than Alternative 1 because of the smaller food supply increase required.  However, the land area expansion is still very large compared to the Real World scenario.  The land expansion under Alternative 2 results in a total of 5,115 acres, as shown in Table 1.

Because of the smaller acreage expansion, total emissions under this scenario are less than under Alternative 1, but still higher than the real world.  Compared to Alternative 2, the yield gains (Real World) achieved since 1961 have avoided 86.5 billion tons of emissions as shown in Table 2.  This is an amount equal to 18 percent of the total anthropogenic emissions from 1850 to 2005.   

Impact of Yield Increasing Research

The investment in agriculture yield increasing research during this time period is estimated to have resulted in avoided greenhouse gas emissions at a cost of approximately $14.74 per metric ton of carbon ($4 per metric ton of carbon dioxide equivalent).  This is a relatively low cost method of controlling greenhouse gas emissions, especially considering that these emission reductions were achieved as a side benefit during a time period when there was little concern about global warming. 

Looking towards the future, world population is expected to increase 37 percent by 2050 and food demand is expected to increase at about twice this rate.  The challenge facing the world’s agricultural community is to meet the food needs of a growing world population while also reducing greenhouse gas emissions.  This can only be met by increasing agriculture yields.  Otherwise, this growing demand will have to be met by converting huge areas of the world’s grasslands and forests to cropland.   As outlined above, land conversion results in substantially more greenhouse gas emissions than yield increasing technology.

So, investments in yield increasing research will provide the food supply for an expanding world population while avoiding large greenhouse gas emissions from land conversion.  Moreover, when yield increasing research is coupled with agricultural research focused on reducing the emissions from yield increasing technologies, the impacts will be even greater.


The agricultural sector has a dual opportunity to meet the food needs of a growing world population while focusing on yield increasing technologies with fewer greenhouse gas emissions.  The combined results of reducing cropland expansion by increasing yields and developing yield technologies with lower emissions can be a powerful force in mitigating the impact of climate change.  However, to accomplish this, substantial public and private sector investments will need to be made in agriculture research and development.  Policy makers need to seriously consider investments in agriculture research as a powerful tool to mitigate climate change while providing the world with an abundant food supply.

For the full research report, go to Greenhouse Gas Mitigation by Agricultural Intensification, Jennifer A. Burney, Steven J. Davis, and David B. Lobell.