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Did Native Americans contribute to global warming?

April 15, 2010
Courtesy of Ohio University
and World Science staff

Early Na­tive Amer­i­cans caused more car­bon di­ox­ide emis­sions than pre­vi­ously thought—and they thus con­tri­but­ed to glob­al warm­ing even be­fore the in­dus­t­ri­al era be­gan, a new study sug­gests.

The in­dig­e­nous peo­ples burned trees as part of for­est-manage­ment strat­e­gies that ul­ti­ma­tely led wood­lands to yield more of the nuts and fruit that the peo­ples ate in abun­dance, ac­cord­ing to sci­en­tists. The re­sult: emis­sions of car­bon di­ox­ide, one of the key heat-trapping gas­es blamed by clim­at­ol­ogists for glob­al warm­ing. 

Present-day forest-burn­ing in the Ama­zon. (Photo cour­tesy US For­est Svc.)
“It was­n’t at the same lev­el as to­day, but it sets the stage,” said Greg­o­ry Spring­er, a ge­ol­o­gist at the Ohio Uni­vers­ity and lead au­thor of the stu­dy, pub­lished in the re­search jour­nal The Hol­o­cene.

The con­clu­sions are based on chem­i­cal anal­y­sis of a stal­ag­mite, or mine­ral growth, found in the moun­tain­ous Buck­eye Creek ba­sin of West Vir­gin­ia. 

Na­tive Amer­i­cans “ach­ieved a pret­ty soph­is­t­ica­ted lev­el of liv­ing that I don’t think peo­ple have fully apprecia­ted,” Spring­er said. “They knew how to get the most out of the for­ests and land­scapes they lived in. This was all across North Amer­i­ca, not just a few loca­t­ions.”

In­i­tial­ly, Spring­er and col­la­bo­ra­tors from Uni­vers­ity of Tex­as at Ar­ling­ton and Uni­vers­ity of Min­ne­so­ta were stu­dying his­tor­ic drought cy­cles in North Amer­i­ca us­ing iso­topes, or vari­ants, of car­bon in stal­ag­mites. To their sur­prise, they said, the car­bon rec­ord con­tained ev­i­dence of a ma­jor change in the lo­cal ec­o­sys­tem be­gin­ning at 100 B.C. This in­trigued the team be­cause an ar­che­o­logical dig in a near­by cave had yielded ev­i­dence of a Na­tive Amer­i­can com­mun­ity there 2,000 years ago.

Spring­er re­cruited two Ohio Uni­vers­ity gradua­te stu­dents to ex­am­ine stream sed­i­ments. With the help of Har­old Rowe of Uni­vers­ity of Tex­as at Ar­ling­ton, he said, the team found very high lev­els of char­coal be­gin­ning 2,000 years ago, as well as a car­bon iso­tope his­to­ry si­m­i­lar to the stal­ag­mite.

This sug­gests Na­tive Amer­i­cans sig­nif­i­cantly al­tered the lo­cal ec­o­sys­tem by clear­ing and burn­ing for­ests, probably to make fields and en­hance the growth of nut trees, Spring­er said. It’s a pic­ture that con­flicts with the pop­u­lar no­tion that early Na­tive Amer­i­cans had lit­tle im­pact on North Amer­i­can land­scapes. They were bet­ter land stew­ards than the Eu­ro­pe­an colo­nial­ists who fol­lowed, he said, but they ap­par­ently cleared more land and burned more for­est than pre­vi­ously thought.

This long-a­go land clear­ing would have im­pacted glob­al clima­te, Spring­er added. On­go­ing clear­ing and burn­ing of the Am­a­zon rainfor­est, for ex­am­ple, is one of the world’s larg­est sources of green­house gas emis­sions. Prehis­tor­ic burn­ing by Na­tive Amer­i­cans was less in­tense, but a non-trivial source of green­house gas­es to the at­mos­phere, he said.

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Early Native Americans caused more carbon dioxide emissions than previously thought—and they thus contributed to global warming even before the industrial era began, a new study suggests. The indigenous peoples burned trees as a forest-mangement strategy that ultimately led woodlands to yield more of the nuts and fruit that the peoples ate in abundance, according to Ohio University scientists who led the study. The result was emissions of carbon dioxide, one of the key heat-trapping gases generally blamed for global warming. “It wasn’t at the same level as today, but it sets the stage,” said Gregory Springer, a geologist at the university and lead author of the study, published in the research journal The Holocene. The conclusions are based on chemical analysis of a stalagmite, or mineral growth, found in the mountainous Buckeye Creek basin of West Virginia. Native Americans “achieved a pretty sophisticated level of living that I don’t think people have fully appreciated,” Springer said. “They knew how to get the most out of the forests and landscapes they lived in. This was all across North America, not just a few locations.” Initially, Springer and collaborators from University of Texas at Arlington and University of Minnesota were studying historic drought cycles in North America using isotopes, or variants, of carbon in stalagmites. To their surprise, they said, the carbon record contained evidence of a major change in the local ecosystem beginning at 100 B.C. This intrigued the team because an archeological excavation in a nearby cave had yielded evidence of a Native American community there 2,000 years ago. Springer recruited two Ohio University graduate students to examine stream sediments. With the help of Harold Rowe of University of Texas at Arlington, he said, the team found very high levels of charcoal beginning 2,000 years ago, as well as a carbon isotope history similar to the stalagmite. This evidence suggests that Native Americans significantly altered the local ecosystem by clearing and burning forests, probably to make fields and enhance the growth of nut trees, Springer said. This picture conflicts with the popular notion that early Native Americans had little impact on North American landscapes. They were better land stewards than the European colonialists who followed, he said, but they apparently cleared more land and burned more forest than previously thought. This long-ago land clearing would have impacted global climate, Springer added. Ongoing clearing and burning of the Amazon rainforest, for example, is one of the world’s largest sources of greenhouse gas emissions. Prehistoric burning by Native Americans was less intense, but a non-trivial source of greenhouse gases to the atmosphere, he said.