Climate and human influences on global biomass burning over the past two millennia

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1 corrigendum Climte nd humn influences on glol iomss urning over the pst two millenni J. R. Mrlon, P. J. Brtlein, C. Crcillet, D. G. Gvin, S. P. Hrrison, P. E. Higuer, F. Joos, M. J. Power nd I. C. Prentice Nture Geoscience, ; pulished online: 2 Septemer 28; corrected fter print: 23 Ferury 29. In this Article, the y xis lel of Fig. 4d ws incorrect; it should hve red ( 6 ). This hs een corrected in the HTML nd PDF versions. 29 Mcmilln Pulishers Limited. All rights reserved.

2 Climte nd humn influences on glol iomss urning over the pst two millenni ARTICLES J. R. MARLON *, P. J. BARTLEIN, C. CARCAILLET 2, D. G. GAVIN, S. P. HARRISON 3, P. E. HIGUERA 4, F. JOOS 5, M. J. POWER 6 AND I. C. PRENTICE 7 Deprtment of Geogrphy, University of Oregon, Eugene, Oregon 9743, USA 2 Centre for Bio-Archeology nd Ecology (UMR559 CNRS/UM2/EPHE), Institut de Botnique, F-349 Montpellier, Frnce 3 School of Geogrphicl Sciences, University of Bristol, Bristol BS8 SS, UK 4 Deprtment of Erth Sciences, Montn Stte University, Bozemn, Montn 5977, USA 5 Climte nd Environmentl Physics, Physics Institute nd Oeschger Centre for Climte Chnge Reserch, University of Bern, CH-32 Bern, Switzerlnd 6 Uth Museum of Nturl History, Deprtment of Geogrphy, University of Uth, Slt Lke City, Uth 842, USA 7 QUEST, Deprtment of Erth Sciences, University of Bristol, Bristol BS8 RJ, UK *e-mil: jmrlon@uoregon.edu Pulished online: 2 Septemer 28; corrected online: 24 Ferury 29; doi:.38/ngeo33 Lrge, well-documented wildfires hve recently generted worldwide ttention, nd rised concerns out the impcts of humns nd climte chnge on wildfire regimes. However, comprtively little is known out the ptterns nd driving forces of glol fire ctivity efore the twentieth century. Here we compile sedimentry chrcol records spnning six continents to document trends in oth nturl nd nthropogenic iomss urning for the pst two millenni. We find tht glol iomss urning declined from AD to 75, efore rising shrply etween 75 nd 87. Glol urning then declined ruptly fter 87. The erly decline in iomss urning occurred in concert with glol cooling trend nd despite rise in the humn popultion. We suggest the susequent rise ws linked to incresing humn influences, such s popultion growth nd lnd-use chnges. Our compiltion suggests tht the finl decline occurred despite incresing ir tempertures nd popultion. We ttriute this reduction in the mount of iomss urned over the pst 5 yers to the glol expnsion of intensive grzing, griculture nd fire mngement. Fire is key Erth system process ffecting ecosystems, lnd-surfce properties, the cron cycle, tmospheric chemistry, erosols nd humn ctivities. Humns mnge fire intensively tody, so it is esy to forget tht fire is nturl process tht hs dominted the ecology of mny terrestril ecosystems throughout their history 3. Empiricl dt on long-term chnges in fire ctivity, prticulrly t rod sptil scles, however, re limited. Historicl records 4, remotely sensed dt 5 nd tree-ring dt from the pst few centuries 6 8 provide most of the informtion out the interctions of fire, climte, vegettion nd people. Climte-chnge projections indicte tht we will e moving quickly out of the rnge of the nturl vriility of the pst few centuries. records from lke sediments enle us to infer the impcts of climte chnges nd humn ctivities on glol iomss urning during periods when oth hve chnged sustntilly. Although hundreds of such records hve een developed during pleoecologicl nlyses 9,, until now no ttempt hs een mde to nlyse them for lrge-scle ptterns nd trends over the pst 2, yers. We present glol nd regionl reconstructions of iomss urned over the pst 2, yers (Figs nd 2) sed on glol sedimentry chrcol dt set (Fig. 3). We interpret temporl ptterns in iomss urned, s indicted y chnges in the input of chrcol to sediments, y comprison with independent reconstructions of humn popultion nd temperture chnges, nd with climte simultions tht mimic the rod fetures of reconstructed temperture chnges. CHARCOAL RECORDS OF BIOMASS BURNING ccumultion in sediments hs een shown,2 to reflect iomss urning within tens of kilometres of the smpling site. We developed regionl nd glol composite strtigrphies sed on 46 chrcol records from lke sediments nd pets. Although there re geogrphic gps, there is good coverge of climtic zones nd of ll the mjor iomes except grsslnd/dry shrulnd (Fig. 3; Supplementry Informtion, Fig. S), where low woody iomss limits chrcol production. Composite records were stndrdized nd trnsformed (see Supplementry Informtion) to represent centennil-scle trends in chrcol ccumultion rtes or influx (in units of quntity re yr ) for the gloe or given region nd to revel the reltive chnges in iomss urned through time. Internnul to decdl vritions re not resolved, so these dt do not record chnges tht might e ttriutle to higher-frequency climte vriility or lnd mngement chnges over the pst few decdes 5,6. The strength of these dt lies in their ility to provide long-term oservtionl record with site coverge tht does not degrde sustntilly with incresing time from the present. nture geoscience VOL OCTOBER Mcmilln Pulishers Limited. All rights reserved.

3 c d e Z-scores of trnsformed chrcol influx ( 6 ) ,, Ref. 8 Men Overlp of reconstructions (including uncertinties) % Northern Hemisphere Gloe Ref. 42 Ref. 44 Ref Temperture nomly ( C) [CO 2 ] (p.p.m.) c d ( 6 km 2 ) ( 6 km 2 ) ( 6 km 2 ) ( 6 km 2 ) Proportion of glol lnd re Totl cultivted lnd Grsslnd (& psture) Croplnd ,,,,,., ( 6 ) ( 6 ) ( 6 ) ( 6 ) Are ( 6 km 2 ) Totl cultivted re Croplnd Psture Yer AD Cl yer BP Yer AD Cl yer BP Figure Reconstructions of iomss urning, climte, popultion nd lnd cover., Reconstruction of glol (red line) nd Northern Hemisphere (purple line) iomss urning with confidence intervls sed on ootstrp resmpling y site. A dshed line is used to represent incresed uncertinty in lte twentieth century chnges in iomss urning., Reconstructions of Northern Hemisphere climte 8 with men vlues (purple line) of ville reconstructions, trend line (dotted line) for first prt of record nd overlp of uncertinty rnges of ten Northern Hemisphere temperture reconstructions fter AD 7 (grey shding). c, World popultion from the HYDE 3. dtse 3. d, Atmospheric CO 2 concentrtion e, Glol griculturl lnd cover 3. The glol sedimentry chrcol record (Fig. ) shows long-term decline in iomss urning from AD to out 75, followed y mrked increse. A mximum, corresponding to the highest iomss-urning rte in the pst two millenni, occurs round AD 87. This mximum is followed y shrp downturn in the composite record. At centennil scles, there is locl mximum in iomss urning t AD tht does not correspond to wrmer tempertures, ut the temperture reconstruction consists of only two records during this period. Biomss-urning minim Figure 2 Zonl chnges in iomss urning, popultion nd lnd cover. d, Chnges in iomss urning (s in Fig. ) with lnd-cover chnge 3, nd proportion of glol ice-free lnd re, for northern extrtropics (>3 N) (), tropics (3 N to 2 S) (), southern extrtropics (>2 S) (c) nd the northern high ltitudes (>55 N) (d). The composite records re sed on t lest sites per region nd thus should revel the dominnt ptterns tht reflect processes operting t lrge sptil scles (see Methods section). occur out AD 4 nd 9, nd t 7, during the Little Ice Age (out 4 8). Our nlyses (see Supplementry Informtion) show tht these ptterns in the glol record re roust nd unffected y differences in record type or smpling resolution, chnges in sedimenttion rtes nd ge model construction, or y the choice of sttisticl techniques used to construct the composite records. The long-term decline in iomss urning efore 75 is most strongly expressed in the northern extrtropics (Fig. 2), prticulrly in western North Americ nd Asi (see Supplementry Informtion, Figs S,S4). The long-term decline is lso chrcteristic of records from Centrl nd tropicl South Americ (Fig. 4), lthough the decrese in iomss urning there occurs erlier ( 3) nd persists longer thn in other regions. In contrst, the tropics nd southern extrtropics show vrile levels of iomss urning to 85, fter which the records show widespred decline in iomss urning (see Supplementry Informtion, Figs S8,S9). Incresed urning in the tropics nd western United Sttes during the pst three decdes hs een widely reported 5,6,3,4. The 698 nture geoscience VOL OCTOBER Mcmilln Pulishers Limited. All rights reserved.

4 Smples per record since 2 kyr BP ,5 9 Megiomes Tree cover, GDD (degree-dys) 7,5 5, 2, AE/PE AE/PE Tropicl forest Wrm-temperte forest Svnn nd dry woodlnd Grsslnd nd dry shrulnd Desert Temperte forest Borel forest Tundr % Figure 3 Distriution of sites in geogrphic, climte nd vegettion spce., Loctions of chrcol records nd numer of smples over the pst 2, yers (see Methods section). Men smpling density is one smple per 7 yers., Distriution of records in ioclimte spce showing loctions plotted ginst growing degree-dys ove C (n of effective wrmth during the growing seson) nd the rtio of ctul to equilirium evpotrnspirtion (n of effective moisture) 45,46, with remotely sensed tree cover 47 nd modelled iome 48 shown for comprison. glol chrcol record does not reflect this for vriety of resons, including dt coverge, methodologicl issues nd chronologicl constrints in core-top sediments. For exmple, mny of the chrcol records from the tropics do not spn the most recent few decdes. In ddition, the geogrphic coverge of lkes nd ogs in the tropics does not overlp well with the res of most severe urning (Fig. 3). However, individul pleofire records ner res of recent severe urning do show incresing chrcol levels towrds present. For exmple, the only site in Klimntn 5, Indonesi, where extensive pet fires occurred, indictes high iomss urning in the pst few decdes. This is true in the western United Sttes s well 6,7. Additionl dt nd regionl syntheses re needed to resolve these ptterns. CLIMATE, POPULATION AND BIOMASS BURNING Comprisons of glol iomss urning with reconstructed nd simulted climte conditions during the pst two millenni show strong similrities until the Industril Revolution, 75 (Fig., Supplementry Informtion, Fig. S5). Reconstructions of Northern Hemisphere men nnul temperture from pleoclimtic evidence 8 show grdul cooling trend from AD to 75. Simulted tempertures show similr decline 9 (see Supplementry Informtion, Fig. S5). Glol nd Northern Hemisphere reconstructed tempertures show locl mxim round nd 4, corresponding to the locl mxim in chrcol influx, nd pronounced decline from 4 to 7 (Fig. ). Over the intervl from to 75, world popultion nd lnd-cover conversion to griculture generlly incresed (Fig. c,e) with very slight century-scle decrese relted to the Blck Deth in Europe (out 3 to 4). growth nd ccompnying lnd-cover chnge therefore do not ccount for the pprent decrese in glol iomss urning during the first phse of the composite record. Conversely, the correspondence etween declining iomss urning nd long-term cooling on hemispheric or glol scles cn e explined y the positive temperture dependence of fuel moisture (nd hence flmmility) nd vegettion productivity (nd hence fuel vilility) in cooler climtes. nture geoscience VOL OCTOBER Mcmilln Pulishers Limited. All rights reserved.

5 c d Crico Bsin Ti (%) Z-scores of trnsformed chrcol influx Americs: Ref. 49 Ref. 5 Ref. 26 Ref. 5 Centrl nd tropicl South Americ: Ref Yer AD Cl yer BP , Figure 4 Comprison of iomss-urning reconstruction for Centrl nd tropicl South Americ with climte nd popultion dt. c, Biomss-urning reconstruction for Centrl nd tropicl South Americ (2 S to 3 N) for the pst, yers (), with oxygen isotope dt from the Quelccy ice core 3 () nd titnium concentrtion from Crico Bsin mrine core 32 (c), oth smoothed s the chrcol records. d, estimtes for the Americs 3 derived from rcheologicl records 26,27,3,49,5. The two crosses re estimtes of the popultion of the Americs efore nd fter Europen contct from ref. 5. Biomss urning shrply incresed round 75; tempertures (Fig., Supplementry Informtion, Fig. S5), greenhouse-gs concentrtions (Fig. d) nd the rtes of lnd-cover conversion nd popultion growth (Fig. c,e) lso egn to increse. Incresing tempertures, rpidly incresing popultion nd lnd-cover conversion nd rising CO 2 (promoting n increse in iomss through CO 2 fertiliztion) could in principle ll hve contriuted to the iomss-urning increse. However, fter 87, shrp δ 8 O ( ) ( 6 ) downturn in iomss urning occurs despite ccelerted increses in temperture nd CO 2, strongly suggesting the involvement of humn ctivity. The decdes following 87 coincide with the period of mximum expnsion of popultion nd griculture (Figs c,e, nd 2), so the iomss-urning decrese eginning then certinly cnnot e explined y reduced humn ctivity. Indeed, this hs een the period of most rpid lnd-use chnge, chrcterized y lrge-scle conversion of ntive vegettion to croplnds nd the widespred introduction of domestic grzing nimls such s cows nd sheep We therefore suggest tht the downturn cn plusily e explined s n effect of lnd-use chnge, resulting in lndscpe frgmenttion nd generlly less flmmle lndscpe in mny regions 23. Active fire suppression since the erly twentieth century hs lso presumly reduced totl iomss urning in recent decdes. Records from the northern high-ltitude regions (polewrd of 55 N) show the generl climte-induced decline nd the post-75 increse in iomss urning chrcteristic of the glol signl ut do not show the recent downturn in iomss urning (Fig. 2d, Supplementry Informtion, Fig. S). This region hs een much less ffected y griculturl expnsion thn regions frther south (Fig. 2), nd is influenced y high-ltitude mplifiction of the glol-wrming signl leding to incresed tempertures, dryness nd greter fire ctivity 24,25. The iomss-urning record from Europe (see Supplementry Informtion, Fig. S3), which hs een suject to griculturl exploittion throughout the pst two millenni, lso fils to show the recent downturn, consistent with our explntion. The regions in which the downturn is most strongly expressed, including western North Americ (see Supplementry Informtion, Fig. S), the tropics (Fig. 2 nd Supplementry Informtion, Fig. S8) nd Asi (see Supplementry Informtion, Fig. S4), re chrcterized y strong intensifiction of lnd mngement since the mid-nineteenth century. Although initil coloniztion my hve een mrked y n incresed use of fire for lnd clernce, the expnsion of intensive griculture nd forest mngement ctivities in these regions ws ssocited with reduced incidence of fire 23. The record of glol iomss urning over the pst 2, yers cn e divided into four distinct intervls: () 75, when climte drove the long-term downwrd trend in iomss urning; (2) 75 to lte nineteenth century, when popultion-driven lnd-cover chnges long with increses in glol tempertures produced the shrp increse in iomss urning, (3) lte nineteenth to mid-to-lte twentieth century, which includes the striking decrese in iomss urning tht ccompnies the decrese in the rte of lnd-cover chnge; nd (4) the pst severl decdes, which is eyond the resolving power of the glol chrcol record, when incresed iomss urning is reported in mny tropicl regions. FIRE AND ATMOSPHERIC CHEMISTRY Ferretti et l. 26 showed n unexpected trend towrds more negtive δ 3 CH 4 vlues from AD to 7 in the Lw Dome ice-core record, nd invoked chnges in iomss urning to explin this trend. They noted the similrity of their δ 3 CH 4 record oth to the Lw Dome record of tmospheric CO concentrtion nd to proxy-sed reconstructions of Northern Hemisphere tempertures. Becuse fire is mjor source of CO nd the min nturl source of reltively 3 C-enriched CH 4, Ferretti et l. postulted declining trend in iomss urning, nd ttriuted it to long-term cooling of the lnd surfce. Houweling et l. 27 expressed scepticism out this possiility nd proposed n lterntive scenrio involving chnging wetlnd emissions, plnt emissions nd erly rice cultivtion to explin the δ 3 CH 4 trend, voiding the impliction of Ferretti et l. of high iomss-urning levels in pre-industril time. Our results 7 nture geoscience VOL OCTOBER Mcmilln Pulishers Limited. All rights reserved.

6 however provide strong empiricl support for the decline in iomss urning since AD proposed y Ferretti et l. 26. Ferretti et l. lso noted n especilly steep fll in δ 3 CH 4 from 5 to 7, nd invoked popultion decline in the Americs s n extr fctor to ccount for it. The glol chrcol record lso shows shrp decrese from 5 to 7, ut glol popultion did not fll during this period (Fig. c). South Americn popultion declined fter 5 (refs 28,29) (Fig. 4), ut comprison of iomss urning, popultion estimtes for the Americs 3 nd climte dt from Anden ice cores 3 nd Crico Bsin titnium concentrtions 32, which is proxy for Atlntic Intertropicl Convergence Zone ltitude nd hence tropicl precipittion trends, suggests tht the lrgest decrese in iomss urning there preceded the popultion decline nd followed regionl climte trends (Fig. 4). The similrities etween the glol chrcol record nd climte proxies suggest continuing climtic control to t lest 75. The pek in glol iomss urning t 87 corresponds to pek in lck cron round 9 oserved in Greenlnd ice; however, McConnell et l. 33 ttriute this to pek in industril emissions. The seprtion of iomss nd fossil components of the lck-cron record, however, rests on the interprettion of the ccompnying vnillic cid record s proxy for glol iomss urning 34 nd, in prt, on the choice of scling fctors etween vnillic cid nd lck cron. Our results strongly suggest tht climte chnge hs een the min driver of glol iomss urning for the pst two millenni. The decline in iomss urning fter 87 is opposite to the expected effect of rising CO 2 nd rpid wrming, ut contemporneous with n unprecedentedly high rte of popultion increse. This suggests tht, during the industril er, mjor impct of humn ctivities hs een to reduce iomss urning through the lrge-scle expnsion of intensive grzing nd cropping with ssocited lndscpe frgmenttion, nd lso ctive fire mngement. However, in regions less dominted y intensive lnd mngement, wildlnd fire hs remined t high levels or incresed s the climte hs wrmed. In the future, it is plusile tht the min impct of humn ctivity on urning will e through nthropogenic climte chnge 35. To ssess this possiility, it will e necessry to improve our understnding of pleoecologicl records of fire nd to develop relile models of the fire regime. Such models should include humn s well s nturl ignitions, ccount for the effects of lnd use s well s climte nd e tested using pleoecologicl nd ice-core dt 36. METHODS Anlyses re sed on 46 sedimentry chrcol records from the Glol Dtse (GCD version ) (ref. ), plus supplementry dt from memers of the Glol Pleofire Working Group tht will e incorported into GCD version 2. Only records from lkes, ogs nd smll hollows were included in our nlyses (see Supplementry Informtion). We exmined the distriution of dt in terms of geogrphic, climtic nd vegettion spce to ensure tht the dt set could e considered resonle representtion of glol iomss urning. Given the unequl distriution of lnd etween the Northern nd Southern hemispheres, the chrcol dt set is resonly representtive of the gloe. Sixty-seven per cent of the sites re in the Northern Hemisphere, which represents 74% of the ice-free lnd re. Nevertheless, some geogrphic regions re less well smpled thn others (Fig. 3). To ssess the glol coverge of the GCD in terms of climte nd vegettion, we plotted individul chrcol sites on top of climte, simulted iomes nd tree cover dt (Fig. 3). The chrcol sites provide resonly representtive smpling of ll the mjor climtic zones, nd of forest iomes (see Supplementry Informtion, Fig. S). Grsslnd/dry shrulnd, svnns nd deserts re under-represented (Fig. 3). There re few nturl fires in desert regions; thus, this under-smpling is not importnt. The pucity of chrcol records from grsslnd nd dry shrulnd nd from svnn reflects the dominnce of low-intensity ground fires in these regions nd the smller numer of lkes present in dry regions. Such low-intensity fires do not consistently leve chrcol record (lthough see ref. 37), nd the totl iomss urned is low compred with forests 38. Thus, the under-smpling of these two vegettion types is unlikely to ffect the composite glol iomss-urning curve significntly. The rod rnge of dt types nd chrcol quntifiction methods, s well s the skewed distriution of most chrcol records, motivted the trnsformtion nd stndrdiztion of the dt efore generting composite records. After testing the impct of severl stndrdiztion nd normliztion techniques, we chose to use modified version (see Supplementry Informtion) of the normliztion nd stndrdiztion procedure descried y Power et l., which resulted in highly roust chrcol summriztions. dt were normlized to stilize the vrince nd stndrdized to mke them comprle cross rod rnge of dt types, smpling nd processing methods. Records were smoothed y fitting lowess curves 39 to the dt in two-stge process tht prevented records with the highest resolution from dominting the glol signl, nd tht voided interpolting dt in the low-resolution records. This pproch lso minimizes the impct of the extreme vlues in sedimentry chrcol dt, which enled us to focus insted on the long-term trends in the dt. Vrious sensitivity nlyses were crried out to ensure tht the composite records were roust to the use of influx versus concentrtion vlues, to the effects of chnging sedimenttion rtes nd to the differences in coverge mong regions (see Supplementry Informtion). We compred the reconstructed chnges in fire regimes with climte proxy records of Northern Hemisphere temperture vritions during the pst 2, yers 8, nd confirmed tht these dt series re sttisticlly correlted during the intervl from to 75 AD (see Supplementry Informtion). We used ten Northern Hemisphere temperture reconstructions sed on multiple climte proxies. These reconstructions differ in () dt type, (2) dt origin (terrestril nd/or mrine), (3) inclusion or exclusion of extrtropicl dt sources, (4) the numer of dt points used in the finl reconstructions, (5) temporl length, (6) sesonl specificity (summer versus men nnul temperture) nd (7) sttisticl methods used to derive the reconstruction. Nevertheless, s shown in the Intergovernmentl Pnel on Climte Chnge Fourth Assessment 8, the reconstructions show rod coherence over the pst,3 yers on centennil timescles, nd the existence of multiple reconstructions mkes it possile to derive confidence limits sed on the degree of coherence etween the ville reconstructions. Here we use the men of the ten ville reconstructions, smoothed with lowess curve. We lso show the uncertinties in the reconstructions. There hve een some ttempts to reconstruct historicl chnges in glol men tempertures 4, nd in Southern Hemisphere tempertures 4. Given the pucity of dt ville from the Southern Hemisphere covering more thn the pst few decdes, comprison of such dt with the reconstructed fire histories is unwrrnted. However, we did compre simulted glol chnges in wrm-seson tempertures nd dry-seson precipittion rtes from the Ntionl Center for Atmospheric Reserch Climte System Model (see Supplementry Informtion, Fig. S5). To explin the vritions in glol iomss urning, we lso compred the chrcol dt with popultion nd lnd-cover dt. World popultion nd lnd-cover dt were otined from the HYDE 3. dtse 3 nd were summrized using lowess curves in mnner similr to the chrcol nd climte dt. Confidence intervls (95%) re lso shown (Fig. ). Received 9 June 28; ccepted 27 August 28; pulished 2 Septemer 28. References. Scott, A. C. The pre-quternry history of fire. Pleogeogr. Pleoclimtol. Pleoecol. 64, (2). 2. Bond, W. J. & Keeley, J. E. Fire s glol herivore : The ecology nd evolution of flmmle ecosystems. Trends Ecol. Evol. 2, (25). 3. Scott, A. C. & Glsspool, I. J. The diversifiction of Pleozoic fire systems nd fluctutions in tmospheric oxygen concentrtion. Proc. Ntl Acd. Sci. USA 3, (26). 4. Westerling, A. L., Hidlgo, H. G., Cyn, D. R. & Swetnm, T. W. Wrming nd erlier spring increse western US forest wildfire ctivity. Science 33, (26). 5. Vn der Werf, G. R., Rnderson, J. T., Giglio, L., Colltz, G. J. & Ksihtl, P. S. Internnul vriility in glol iomss urning emission from 997 to 24. Atmos. Chem. Phys. 6, (26). 6. Mouillot, F. & Field, C. B. Fire history nd the glol cron udget: fire history reconstruction for the 2th century. Glo. Chnge Biol., (25). 7. Swetnm, T. W. & Betncourt, J. L. Mesoscle disturnce nd ecologicl response to decdl climtic vriility in the Americn southwest. J. Clim., (998). 8. Girrdin, M. P. & Suchyn, D. Three centuries of nnul re urned vriility in northwestern North Americ inferred from tree rings. Holocene 8, (28). 9. Crcillet, C. et l. Holocene iomss urning nd glol dynmics of the cron cycle. Chemosphere 49, (22). nture geoscience VOL OCTOBER Mcmilln Pulishers Limited. All rights reserved.

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Res. 8, 87 (23). 49. McEvedy, C. & Jones, R. Atls of World History (Hrmondsworth, New York, 978). 5. Ruddimn, W. F. Plows, Plgues nd Petroleum: How Humns Took Control of Climte (Princeton Univ. Press, Princeton, 25). 5. Denevn, W. M. The Ntive of the Americs in 492 (Univ. of Wisconsin Press, Mdison, 992). Supplementry Informtion ccompnies the pper t Acknowledgements This rticle is contriution to the Glol Pleofire Working Group (GPWG) of the Interntionl Geosphere-Biosphere Project Cross-Project Inititive on Fire. The GPWG is supported y the UK Nturl Environment Reserch Council s QUEST (Quntifying Uncertinty in the Erth System) progrmme. Dt compiltion nd nlysis were supported y the QUEST-Deglcition project (M.J.P., S.P.H.) nd y the US Ntionl Science Foundtion Pleoclimtology (P.J.B.) nd Geogrphy nd Regionl Science progrms (P.J.B. nd J.R.M.). We thnk our collegues who hve mde these nlyses possile through their contriutions to the Interntionl Multiproxy Pleofire Dtse nd the Glol Dtse. Author contriutions S.P.H. proposed the ide of 2 yer synthesis. J.R.M, M.J.P., P.J.B., F.J. nd S.P.H. compiled the dt. P.J.B. crried out the nlyses with ssistnce from P.E.H., D.G.G. nd J.R.M. All uthors contriuted to writing the pper. Author informtion Reprints nd permissions informtion is ville online t Correspondence nd requests for mterils should e ddressed to J.R.M. 72 nture geoscience VOL OCTOBER Mcmilln Pulishers Limited. All rights reserved.