Agriculture Reduces Greenhouse Gases

Often a target for environmentalists and global warming alarmists alike, intensive modern agriculture has been demonized as the cause of many types of pollution, including those dreaded greenhouse gases. A study, soon to appear in the Proceedings of the National Academy of Sciences (PNAS), reveals that highly productive modern agriculture actually reduces net greenhouse gas emissions when compared with using croplands less intensively. Furthermore, expansion of agriculture, needed to feed mankind's ever growing numbers, can help reduce future increases in CO2 emissions. Looks like the doomsayers got it backwards again, more intensive agricultural is a good thing for the environment. In fact, agriculture reduced total human carbon emissions from 1850 to 2005 by 34%.

Agriculture is generally considered a source of greenhouse gas emissions, not a possible tool for GHG mitigation. In recent years, fears over the impact of increasing agricultural production have centered on accelerated release of methane (CH4), nitrous oxide (N2O) and oxides of nitrogen (NOx), as well as CO2. Even the pesky weed kudzu has been pointed to as contributing to global warming. Fortunately, kudzu is no longer planted for erosion prevention or as fodder for animals, at least in the US.

Just a year ago, the EU issued a press release that proclaimed “global greenhouse emissions are currently increasing, and agriculture accounts for between 5 and 26 per cent of EU Member States’ total emissions.” The ministers stressed the importance of reducing the impact of agriculture on the climate, both globally and at EU level. Combine feeding humanity with growing concerns about future shortages of freshwater and public concern over climate change has greatly receded. Even so, the impact of global farm activity remains a concern.


You can't get much greener than this.

Future agricultural productivity is critical, since it will shape emissions from conversion of native landscapes to food and other crops. Until now, investment in agricultural research has rarely been mentioned as a mitigation strategy. In “Greenhouse gas mitigation by agricultural intensification,” Jennifer A. Burney, Steven J. Davis and David B. Lobella argue convincingly that agriculture holds the key to reducing humanity's CO2 emissions. They state their hypothesis in the paper's abstract:

Here we estimate the net effect on GHG emissions of historical agricultural intensification between 1961 and 2005. We find that while emissions from factors such as fertilizer production and application have increased, the net effect of higher yields has avoided emissions of up to 161 gigatons of carbon (GtC) (590 GtCO2e) since 1961. We estimate that each dollar invested in agricultural yields has resulted in 68 fewer kgC (249 kgCO2e) emissions relative to 1961 technology ($14.74/tC, or ~$4/tCO2e), avoiding 3.6 GtC (13.1 GtCO2e) per year. Our analysis indicates that investment in yield improvements compares favorably with other commonly proposed mitigation strategies. Further yield improvements should therefore be prominent among efforts to reduce future GHG emissions.

According to the paper, The main components of agricultural emissions outside of land use change are nitrous oxide (N2O) released from soils related to the application of nitrogenous fertilizer (38%), methane (CH4) from livestock , CH4 and N2O from manure (38%), CH4 from cultivation of rice (11%), and CH4 and N2O from burning of savannah, forest, and agricultural residues (13%). Note that in the quote above the authors are lumping all of these gas emissions into CO2 “equivalent” amounts (CO2e), which are based on IPCC estimates of how potent greenhouse gases are in terms of equivalent amounts of carbon dioxide. In addition to these direct emissions sources, agricultural activity drives emissions in the industrial and energy sectors through production of fertilizers and pesticides, production and operation of farm machinery, and other farm energy use.

To judge the impact of improved farming technology and increasing crop yields, Burney et al. compared real world (RW) changes from 1961 to 2005 with two modeled scenarios, labeled AW1 and AW2. The AW1 scenario addresses the question of what it would cost, in terms of GHG impact, to achieve the current global standard of living without crop yield improvements. It assumes the same crop yields and fertilizer application rates as in 1961, and scales land use and fertilizer production accordingly. The AW2 scenario simply maintains the 1961 standards of living in the face of a growing world population, again by expanding land use instead of improving crop yields. This scenario provides a reasonable lower bound on carbon savings. The modeled results are shown in the figure below.


Comparison of trends in the RW and AW scenarios between 1961 and 2005. Burney et al.

The AW1 scenario resulted in development of an additional 6.8 million square miles (1,761 Mha) of cropland, an area larger than Russia. This is 5.85 million mi2 (1,514 Mha) more cropland than was added in the real world. The impacts of the AW2 scenario were roughly half those of the AW1 scenario, but still worse than what actually happened in the real world. Bottom line, GHG emissions in the AW1 scenario were much greater, dominated by the effect of land use change. The implication is that yield gains in agriculture since 1961 have avoided emissions of 161 GtC (+104.2/−41.9 GtC), or an average of 3.6 GtC/yr (+2.3/−0.9 GtC/yr). This corresponds to 34% of the total 478 GtC emitted by humans between 1850 and 2005.

What the study found was that improved crop yields have maximized land use efficiency and minimized the need for clearing more farmland. “Enhancing crop yields is not incompatible with a reduction of agricultural inputs in many circumstances,” state the authors. “To the contrary, careful and efficient management of nutrients and water by precision farming, incorporation of crop residues, and less intensive tillage are critical practices in pursuit of sustainable and increased agricultural output.” Not that yield gains alone necessarily preclude expansion of cropland. The report suggests that agricultural intensification must be coupled with conservation and development efforts for best results. Nonetheless, continuing improvement of crop yields was found to be the most important single factor.

The report's conclusions have been corroborated by recent information from Europe. The European Commission has been working on a plan for future agricultural development. Their website states: “EU agricultural emissions of methane and nitrous oxide declined by 20.2% in the period 1990-2007. Large reductions occurred in the greatest sources of emissions, nitrous oxide from agricultural soils and methane emissions from enteric fermentation by cattle, which both fell by about 21%.” So the news from the EU is supportive. Burney et al. summed up their findings this way:

The global population is expected to reach 8.9 billion by 2050, with food demand expected to rise by 70%. Even if yield gains over the next four decades are smaller than those of the previous four decades, the potential to avoid future emissions may be larger and more cost-effective than the 161 GtC of emissions avoided thus far, given that current cropland expansion often occurs in tropical forests and that the remaining forests are carbon-rich relative to many cleared forests. Improvement of crop yields should therefore be prominent among a portfolio of strategies to reduce global greenhouse gas emissions; in order to speed the adoption of agronomic advancements that improve crop yield, mechanisms for connecting investments in yield gains to the global carbon markets should be explored.

Not only does human agriculture reduce GHG emissions today, Burney et al. suggest that in the future will reduce potential emissions even more. Benefits of intensive agriculture include reducing the need to clear tropical forests, which have been religiously defended against development by greens world wide. In view of this new work, it seems that expanding agriculture intelligently is the path to a greener future, and not an example of mankind raping the land. And, if you are worried about global warming, it looks like farming may be part of the solution, not a part of the problem.

As encouraging as these findings are, they do not change the fact the raising crops for biofuels is a losing proposition. While clearing land, even tropical forest, for agricultural purposes may make sense, doing so to raise biofuel feedstock does not. With the ever rising need for freshwater for growing food crops, diverting resources into biofuel production is the height of folly.


Modern agriculture in Shanghai.

More than a decade ago, activists from various green causes came together under the umbrella of anthropogenic global warming. Each group had its own pet concerns: polar bears, sinking tropical islands, emissions from fossil fuels, clearing of forests and agricultural production, to name a few. Even vegetarians joined the throng of climate change alarmists.

AGW was seen as a “big tent” under which these various green causes could gather. The forces of eco-sensitivity would advance, riding on the coattails of climate change hysteria. Victorious under the banner of the IPCC, they would usher in a new green future based on appropriate technology, sustainable lifestyles and reduced carbon footprints. Then the chimerical witch's brew of ecological issues began falling apart.

One by one, the “problems” were shown to be exaggerated or untrue. The seas have not risen, polar bears have not died out and glaciers refuse to disappear. Now we know intensive modern agriculture eases deforestation pressure and results in significantly lower GHG emissions. It looks like we can remove most of the concerns about modern farming from the list—more warmest lies, disproven by science.

Be safe, enjoy the interglacial and stay skeptical.

Stellar Work

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