Why the Anthropocene has divided the scientific community

The term is eve­ryw­here : from the École de l’Anthropocène in Lyon to a dedi­ca­ted IGN atlas¹ and even two dedi­ca­ted scien­ti­fic jour­nals², eve­ryone – scien­tists inclu­ded – is using the concept of the Anthro­po­cene. This new geo­lo­gi­cal era is cha­rac­te­ri­sed by a signi­fi­cant glo­bal human foot­print on the pla­net. But the term is not offi­cial­ly reco­gni­sed. In March 2024, the Inter­na­tio­nal Com­mis­sion on Stra­ti­gra­phy – the orga­ni­sa­tion res­pon­sible for defi­ning the geo­lo­gi­cal time scale – rejec­ted the offi­cial addi­tion of a new geo­lo­gi­cal era³. We are the­re­fore still offi­cial­ly in the Holo­cene era, as we have been for the past 11,700 years. None­the­less, this deci­sion has not put an end to the debate within the scien­ti­fic community.

True : Part of the scientific community recognises its existence.

Erle Ellis. The Anthro­po­cene, as defi­ned in dic­tio­na­ries, exists and is wide­ly used in science to define a time when humans are trans­for­ming the pla­net. Howe­ver, there is no offi­cial era in the geo­lo­gi­cal timeline.

Michel Magny. A large part of the inter­na­tio­nal scien­ti­fic com­mu­ni­ty reco­gnises the term. When it was first pro­po­sed in our team, which works on the recons­truc­tion of past envi­ron­ments in rela­tion to socie­ties, we had the impres­sion that all our work incor­po­ra­ted the concept of the Anthro­po­cene ! We have seen the major impact of human­kind on eco­sys­tems since the first agri­cul­tu­ral socie­ties. Many geo­lo­gists also reco­gnise the exis­tence of the Anthropocene.

Without dis­pu­ting the fact that rapid and far-rea­ching cli­mate changes may have occur­red in the past, the Anthro­po­cene marks a sud­den change in the cli­mate pat­tern. Whe­reas for a mil­lion years, cli­ma­tic oscil­la­tions were main­ly dri­ven by the Earth’s orbi­tal fac­tors, now it is the rate of human green­house gas emis­sions that is cau­sing the cli­mate to warm up by a simi­lar amount.

False : The International Committee for Stratigraphy has rejected the adoption of the Anthropocene as a geological epoch.

Jan Pio­trows­ki. There is no jus­ti­fi­ca­tion for ending the Holo­cene. The end of the last Ice Age – rough­ly coin­ci­ding with the begin­ning of the Holo­cene – was mar­ked by envi­ron­men­tal changes that were signi­fi­cant­ly grea­ter than those that would have mar­ked the begin­ning of the Anthro­po­cene. For example, the tem­pe­ra­ture rose by 1°C per decade in Wales 15,000 years ago ; 11,700 years ago in Green­land, a war­ming of 7°C occur­red in just 50 years ; and 14,000 years ago, the docu­men­ted rise in sea level in Bar­ba­dos was 40 mm/year. These rates of change are grea­ter than those our pla­net has expe­rien­ced since 1950.

Unclear : There are other alternatives for characterising humanity’s footprint on the planet.

JP. The only valid alter­na­tive to the Anthro­po­cene is to des­cribe it not as an epoch but as an event. Events are ele­ments that are well esta­bli­shed in stra­ti­gra­phy : we find, for example, the Great Oxi­da­tion 2.4 bil­lion years ago, or the Ordo­vi­cian bio­lo­gi­cal explo­sion 500 mil­lion years ago. An event can be dia­chro­nic, as is the case with the Anthro­po­cene. [Edi­tor’s note : The Anthro­po­cene wor­king group says it has consi­de­red this pos­si­bi­li­ty in detail, and concludes that it is incom­pa­tible with the stra­ti­gra­phic data⁴.]

True : Scientists have defined a marker for the start of the Anthropocene.

MM. A wor­king group dedi­ca­ted to the Anthro­po­cene was set up in 2009 at the request of the Inter­na­tio­nal Union of Geo­lo­gi­cal Sciences. In 2019, this group pro­po­sed adop­ting the term Anthro­po­cene. In 2023, it even defi­ned a gol­den spike in the sedi­ments of Lake Craw­ford, in Cana­da. Here, and across the globe, there has been a rapid increase in the concen­tra­tions of two iso­topes of plu­to­nium, cor­res­pon­ding to the first nuclear tests on land. The begin­ning of the Anthro­po­cene would thus be defi­ned in 1952. Apart from the nuclear mar­ker, many other indi­ca­tors show an abrupt change at this time : green­house gas levels rising, bio­di­ver­si­ty fal­ling, pol­lu­tion piling up, man-made waste (such as plas­tic) accumulating.

Some have cri­ti­ci­sed the choice of Lake Craw­ford to define the gol­den spike mar­king the begin­ning of the Anthro­po­cene, main­ly because of its lack of acces­si­bi­li­ty. But what about the site offi­cial­ly cho­sen for the Gol­den Spike at the start of the Holo­cene ? It’s a bore­hole in the Green­land ice cap, which is in dan­ger of disap­pea­ring because of glo­bal warming…

False : It is not possible to precisely define the beginning of the Anthropocene.

JP. There are geo­lo­gi­cal traces of human pre­sence well before the pro­po­sed start of the Anthro­po­cene (begin­ning of agri­cul­ture, set­tle­ment of the Ame­ri­cas, indus­trial revo­lu­tion, etc.). Among the argu­ments against reco­gni­sing the Anthro­po­cene as a geo­lo­gi­cal epoch, seve­ral concern the begin­ning of the Anthro­po­cene. It can­not be pre­ci­se­ly defi­ned because it began at dif­ferent times and in dif­ferent places on Earth. What’s more, the pro­po­sed date (1952) makes no sense, as humanity’s impact on the Earth goes back much fur­ther than that. This would make the Second World War pre-Anthro­po­cene ! Final­ly, the pro­po­sed gol­den spike – Lake Craw­ford – does not meet the stan­dards of the geo­lo­gi­cal time­line : it is not very acces­sible and geo­lo­gi­cal­ly unstable.

EE. It’s poten­tial­ly pos­sible to pre­ci­se­ly define a date and mar­ker for the Anthro­po­cene, but there’s no obvious scien­ti­fic point to it, espe­cial­ly if it’s recent. There are bet­ter ways of unders­tan­ding the Anthro­po­cene as an ongoing pro­cess and event, rather than an abrupt glo­bal change that occur­red in 1952.

Uncertain : Conflicting positions remain, not always based on scientific evidence.

MM. The deci­sion by the Inter­na­tio­nal Com­mis­sion on Stra­ti­gra­phy to refuse to reco­gnise the Anthro­po­cene may seem sur­pri­sing. In fact, in 2023, the dedi­ca­ted wor­king group had recom­men­ded the adop­tion of the Anthro­po­cene and pro­po­sed a gol­den spike.

But I unders­tand the geo­lo­gists’ mis­gi­vings. First, it should be remem­be­red that the Anthro­po­cene epoch was pro­po­sed in 2000 by Paul Josef Crut­zen. This che­mist, who works on stra­tos­phe­ric ozone, is reco­gni­sed by the inter­na­tio­nal scien­ti­fic com­mu­ni­ty and has been awar­ded the Nobel Prize for Che­mis­try. But he is not a geo­lo­gist. The fact that a che­mist is pro­po­sing to revi­sit the geo­lo­gi­cal time­line can be a source of dif­fi­cul­ty. Final­ly, geo­lo­gi­cal time­lines are very long, often mil­lions of years. The change of scale here is radi­cal, with the Anthro­po­cene star­ting in 1952, i.e. only 72 years ago !

True : The term unites many scientists.

MM. The inter­na­tio­nal scien­ti­fic com­mu­ni­ty sei­zed on the term as soon as it was pro­po­sed. There are dedi­ca­ted jour­nals, and major scien­ti­fic jour­nals such as Nature and The Holo­cene have devo­ted spe­cial issues to the Anthro­po­cene. The term brings toge­ther scien­tists from the natu­ral and human sciences, and it is a ban­ner that car­ries weight with the autho­ri­ties that govern us, and we will conti­nue to use it. In my view, refu­sing offi­cial recog­ni­tion sends out a nega­tive signal to scien­tists, but above all to poli­ti­cal and eco­no­mic lea­ders and to public opi­nion. I fear that it will serve as an ali­bi for inac­tion in the face of cli­mate change. It’s a real source of confu­sion, which is to be deplored.

EE. I think that scien­tists will conti­nue to dis­cuss the mea­ning of the “human era” using the term Anthro­po­cene, and pro­ba­bly others. Human socie­ties are not the first or only glo­bal change to the pla­net cau­sed by orga­nisms, but it is the most recent and is dif­ferent from pre­vious ones in many ways. There is no need to for­mal­ly define the Anthro­po­cene epoch for the dis­cus­sion to continue.

Uncertain : Debate is part of the scientific method, and this decision is not final.

MM. Des­pite the deci­sion of the Inter­na­tio­nal Com­mis­sion on Stra­ti­gra­phy, the debate conti­nues. As scien­tists, we are used to seeing nar­ra­tives and inter­pre­ta­tions evolve as the data pro­gresses, and I think that as the eco­lo­gi­cal cri­sis inten­si­fies, the break mar­ked by the Anthro­po­cene will become more and more obvious.

JP. There’s nothing wrong with using the Anthro­po­cene as a scien­ti­fic term, but it should be cal­led an event rather than an epoch. If the Anthro­po­cene star­ted only 70 years ago, then its future impact is based on pre­dic­tions and not on avai­lable geo­lo­gi­cal data. Conse­quent­ly, its sta­tus should be confir­med by future gene­ra­tions of geologists.

Anaïs Marechal