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Human-caused climate change
since c. 1850; fastest since the 1970s· Extinction or crisis· Earth, climate & extinctions
Well establishedStrong fossil, genetic or geological evidence.
Warming of Earth since about 1850, caused mainly by carbon dioxide and methane released by human activity.
See it on the Life map →What happened
Burning coal, oil and gas, plus clearing forests and raising livestock, has raised carbon dioxide from about 280 parts per million before 1850 to over 420 today, the highest in at least 800,000 years. Earth has warmed about 1.3°C on average, and 2024 was the first calendar year above 1.5°C. Seas are rising and about 30% more acidic. Species are shifting toward the poles and uphill, and coral reefs suffer repeated mass bleaching.
Why it matters
It changes conditions faster than many species can move or adapt, worsening the extinction crisis, and it is a live version of past carbon-release crises.
The evidence (fossils, genes, rocks)
Thermometer records since about 1850, satellites, ocean floats and ice cores; the physics of heat-trapping gases has been known since John Tyndall's 1859 experiments. The UN climate panel (IPCC) calls human influence 'unequivocal'.
Still debated
How sensitive climate is to carbon dioxide (likely about 2.5–4°C per doubling), how ice sheets and ocean currents will respond, and how fast ecosystems can adapt.
Connections (5)
▸Siberian Traps eruptions is an ancient analogue for Human-caused climate changeStrong evidence
The connection
The Siberian eruptions released enormous amounts of carbon dioxide and methane, much of it baked out of buried coal and limestone. The world warmed, oceans acidified and lost oxygen, and the Great Dying followed. Today's emissions may be as fast or faster each year, though far smaller in total so far, making the eruptions a warning case.
When and how
Siberia, about 252 million years ago, over roughly a million years; the comparison comes from geochemists studying Permian rocks in China, Italy and elsewhere.
How sure are we?
Carbon-isotope shifts, warming recorded in oxygen isotopes of fossil conodont teeth, and acidification signals in boron isotopes all line up with precisely dated eruptions.
Debates and open questions
How fast the carbon came out in the deadliest pulses compared with today's rate, and whether modern emissions could trigger similar feedbacks.
▸PETM: a sudden hothouse is a past model for Human-caused climate changeStrong evidence
The connection
About 56 million years ago, thousands of billions of tonnes of carbon entered air and oceans within a few thousand years, warming the planet roughly 5–8°C and acidifying seas. Scientists use it to gauge how Earth responds to a carbon pulse. Today's emissions are roughly ten times faster, though the total released so far is smaller.
When and how
Discovered in 1991 by James Kennett and Lowell Stott in deep-sea cores from off Antarctica; since studied in ocean cores and rocks such as Wyoming's Bighorn Basin.
How sure are we?
A sharp drop in carbon-13 in shells and soils marks the carbon release; oxygen isotopes record warming; dissolved seafloor carbonate shows acidification.
Debates and open questions
Where the carbon came from (volcanic heating of buried sediments, methane ice, thawing permafrost) and exactly how its pace compares with today's.
▸Cattle & farm animals domesticated add methane to Human-caused climate changeWell established
The connection
Cattle, sheep and goats are ruminants: microbes in their multi-chambered stomachs break down grass and release methane, which the animals belch. Over 20 years methane traps about 80 times as much heat as carbon dioxide, though it breaks down within about a decade. Livestock produce roughly a third of human-caused methane; clearing forest for pasture adds carbon dioxide.
When and how
Worldwide, rising with herd numbers, now about 1.5 billion cattle; global atmospheric methane measured systematically since the 1980s.
The evidence
Measurements of animals' breath and of farms, plus atmospheric records showing methane at about 2.6 times preindustrial levels; isotopes help separate livestock from other sources.
Debates and open questions
How much of methane's recent rapid rise comes from livestock versus wetlands, rice paddies and fossil-fuel leaks; feed additives that cut emissions are being tested.
▸Industrial Revolution & fossil fuels caused Human-caused climate changeWell established
The connection
Burning fossil fuels returns long-buried carbon to the air as carbon dioxide. Since about 1850 humans have added roughly 2.5 trillion tonnes of CO2, mostly from coal, oil and gas, with forest clearing adding the rest. That has raised concentrations about 50% and trapped extra heat, warming Earth about 1.3°C so far.
When and how
Worldwide since about 1850, accelerating after 1950; Britain led early emissions, the United States has the largest cumulative total, and China now emits the most each year.
The evidence
Carbon isotopes in the air show the extra CO2 is fossil carbon, low in carbon-14 and carbon-13; emissions inventories match the measured rise.
Debates and open questions
There is little scientific dispute that it caused the warming; open questions are future emissions, how sensitive climate is, and how fast feedbacks such as permafrost thaw will act.
▸Human-caused climate change worsens A sixth mass extinction?Strong evidence
The connection
Climate change adds to habitat loss, hunting and invasive species. Warming pushes species toward the poles and uphill; those with nowhere to go, such as mountaintop and polar species, are squeezed. Reef corals bleach in marine heatwaves. The Bramble Cay melomys, a small Australian rodent, is considered the first mammal extinction caused mainly by climate change.
When and how
Worldwide; the Bramble Cay melomys, in Australia's Torres Strait, was confirmed extinct in 2016; global coral bleaching events struck in 1998, 2010, 2014–17 and 2023–25.
How sure are we?
Field studies document thousands of species shifting ranges; repeated reef bleaching tracks measured heatwaves; rising sea and storm surges wiped out the melomys's tiny island habitat.
Debates and open questions
How many species warming will eliminate; the IPCC puts about 3–14% of land species at very high risk at 1.5°C, rising steeply with further warming.