What If Gone

Species → Human Species

Human Species

Homo sapiens

8,300,000,000 individuals (global population)
Extinction risk Not Evaluated
Climate changeCarbon
Human Species (Homo sapiens)
Photo: NASA/DMSP (Marc Imhoff, Christopher Elvidge), Wikimedia Commons (Public domain)

What if it disappeared?

Impact Major
A few weeks (lockdowns)

A brief, worldwide slowdown in human activity — the spring 2020 lockdowns — was enough to cut global CO2 emissions by 17% at the peak of the drop, and to directly measure behavioral changes in dozens of wild species, from elusive wildlife reappearing in cities to different vocalizations in urban birds.

Documented
Detail

Le Quéré, C., Jackson, R.B., Jones, M.W. et al. (2020). Temporary reduction in daily global CO2 emissions during the COVID-19 forced confinement. Nature Climate Change, 10, 647–653.

The term "anthropause," coined by a team of researchers in 2020 (Rutz et al., Nature Ecology & Evolution) to describe precisely this measurable slowdown in human activity, made the journal's September 2020 cover. The measured emissions drop is the largest ever recorded in peacetime — and it fully rebounded as activity resumed in late April 2020, direct proof that the effect tracks ongoing human activity rather than a structural shift.

A few years to a decade

Deprived of maintenance, human infrastructure would start falling apart almost immediately: the power grid would go dark within days, basement and subway pumps would stop running and flooding would follow, then freeze-thaw cycles would crack pavement and the first trees would break through abandoned parking lots within a decade.

Extrapolated
Detail

Extrapolation à partir des taux connus de corrosion, de dégradation des matériaux et de cycles gel-dégel documentés en ingénierie civile — aucune expérience de retrait humain à l'échelle d'une ville entière n'a évidemment été menée.

This scenario, popularized by Alan Weisman's book The World Without Us (2007) and the documentary series Life After People, draws on real material-degradation data (steel rust, wood rot, asphalt freeze-thaw) rather than direct observation of an entire abandoned city. The closest real partial case is Pripyat, the city evacuated in 1986 near Chernobyl, whose decay over nearly four decades confirms the scenario's general direction — without covering every climate or every scale of city.

What's missing to confirm it: No entire city has been observed over decades following a total, simultaneous human abandonment across varied climates; partial cases (Pripyat, deserted neighborhoods of Detroit) illustrate the mechanism without confirming it at global scale.

30-plus years

The one real, large-scale case of prolonged human withdrawal already exists: in the Chernobyl Exclusion Zone, abandoned by 116,000 people in 1986, large mammals (elk, roe deer, red deer, wild boar) reach densities comparable to nearby uncontaminated nature reserves, and wolves are more than seven times as abundant.

Documented
Detail

Deryabina, T.G., Kuchmel, S.V., Nagorskaya, L.L. et al. (2015). Long-term census data reveal abundant wildlife populations at Chernobyl. Current Biology, 25(19), R824–R826.

The study draws on aerial censuses and track surveys spanning decades, compared against four uncontaminated nature reserves in the region. The finding isn't that radiation is harmless — it has measurable effects on some organisms — but that the removal of hunting, farming, forestry, and roads outweighs residual contamination as a pressure on wildlife. It is the closest real-world case to a full human-withdrawal experiment at the scale of an entire landscape.

A century and beyond

Over a century, most cities would revert to forest and the bulk of infrastructure would disappear; but some traces would persist for millennia — the magnetic signature of steel rebar in concrete, plastics, and nuclear waste that will remain hazardous for tens of thousands of years.

Extrapolated
Detail

Synthèses d'ingénierie et de vulgarisation scientifique (Weisman 2007 ; BBC Science Focus ; Popular Science) croisant des données de corrosion, de décomposition des polymères et de radioactivité résiduelle — pas une étude unique et continue sur un siècle, qui par nature n'existe pas encore.

The return of atmospheric carbon to pre-industrial levels would itself take centuries to millennia according to existing climate models, long after the buildings themselves are gone — two very different clocks running in parallel, one for the built environment and one for the climate.

What's missing to confirm it: No complete century-long trajectory has ever been observed anywhere: every source combines partial estimates (corrosion, polymers, climate) that have never been tracked together at a single site abandoned for that long.

Documentation

Last verified: August 14, 2026