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    Green re­volu­tion feeds con­tin­ent, tames cli­mate change

    Major steps in high-yield ag­ri­cul­ture achieved dur­ing the so-called Green Re­volu­tion have not only helped feed the planet, but also have helped slow the pace of global warm­ing by cut­ting the amount of bio­mass burned ac­cord­ing to a re­cent study.

    Ac­cord­ing to the study led by two Stan­ford Earth sci­ent­ists, 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.

    The yield im­prove­ments re­duced the need to con­vert forests to farm­land, a pro­cess that typ­ic­ally in­volves burn­ing of trees and other plants, which gen­er­ates car­bon di­ox­ide and other green­house gases. 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 will be 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 per­cent 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 per­cent 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."
    David Lo­bell is a Cen­ter Fel­low at the Free­man Spogli In­sti­tute for In­ter­na­tional Stud­ies and at the Woods In­sti­tute for the En­vir­on­ment. The Pro­gram on Food Se­cur­ity and the En­vir­on­ment is a joint pro­ject of the Woods In­sti­tute and the Free­man Spogli In­sti­tute. The Pro­gram on Food Se­cur­ity and the En­vir­on­ment provided fund­ing for Jen­nifer Bur­ney's re­search on ag­ri­cul­ture and en­ergy.

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