Are humans responsible for climate change?

Humans and climate change — I'll gather the latest scientific consensus to answer that.

Yes, according to the overwhelming scientific evidence and consensus, humans are the principal cause of the current, rapid climate change.

Scientific Consensus

There is unequivocal evidence that Earth is warming at an unprecedented rate. Human activity is the principal cause.

•Nearly all actively publishing climate scientists say humans are causing climate change.

•The vast majority of actively publishing climate scientists – 97 percent – agree that humans are causing global warming and climate change.

•A 2019 review of scientific papers found the consensus on the cause of climate change to be at 100%, and a 2021 study concluded that over 99% of scientific papers agree on the human cause of climate change.

•More than 99.9% of peer-reviewed scientific papers agree that climate change is mainly caused by humans, according to a new survey of 88,125 climate-related studies.

What the IPCC Concludes

The Intergovernmental Panel on Climate Change (IPCC) was formed to provide internationally coordinated scientific assessments of climate change.

Successive IPCC reports have strengthened the language on human responsibility:

•The IPCC report says there is 95 percent certainty that humans have caused most of the warming of the planet's surface that has occurred since the 1950s — up from 90 percent certainty in the last assessment report, which came out in 2007.

•Among the central findings of the AR6 WGI was the following: "It is unequivocal that human influence has warmed the atmosphere, ocean, and land."

•The IPCC AR6 concludes that it is unequivocal that humans have caused the earth’s climate to warm, with a likely human contribution of 0.8 to 1.3 degrees Celsius to global mean temperature since the late 1800s.

How Humans Cause Warming

Yes, by increasing the abundance of greenhouse gases in the atmosphere, human activities are amplifying Earth’s natural greenhouse effect. Virtually all climate scientists agree that this increase in heat-trapping gases is the main reason for the 1.8°F (1.0°C) rise in global average temperature since the late nineteenth century.

Carbon dioxide, methane, nitrous oxide, ozone, and various chlorofluorocarbons are all human-emitted heat-trapping gases. Among these, carbon dioxide is of greatest concern to scientists because it exerts a larger overall warming influence than the other gases combined.

The mechanism is:

> Observed increases in well-mixed greenhouse gas (GHG) concentrations since around 1750 are unequivocally caused by human activities.

At present, humans are putting an estimated 9.5 billion metric tons of carbon into the atmosphere each year by burning fossil fuels, and another 1.5 billion through deforestation and other land cover changes. Burning fossil fuels like coal and oil puts more carbon dioxide into our atmosphere, causing the atmosphere to trap more heat.

Human vs. Natural Drivers

Natural climate variability and natural drivers (changes in solar activity, volcanic eruptions, and internal variability) exist, but their contribution to recent warming is small:

•It is likely that well-mixed GHGs contributed a warming of 1.0°C to 2.0°C, other human drivers (principally aerosols) contributed a cooling of 0.0°C to 0.8°C, natural drivers changed global surface temperature by –0.1°C to +0.1°C, and internal variability changed it by –0.2°C to +0.2°C.

•Human-caused drivers of both warming and cooling are the largest of these drivers, with the warming effect of human-emitted well-mixed GHGs being the largest of all.

In other words, without human influence, natural factors alone would have caused slight cooling or little change over the past 50 years, while human greenhouse gas emissions account for 100% or more of the observed warming when offset by human aerosol cooling.

Climate has changed naturally in the geologic past due to orbital changes, solar variation, and volcanism, but the current widespread and rapid changes in the atmosphere, ocean, cryosphere and biosphere since about 1750 are assessed as unequivocally human-driven.

Citations (4)

1nasa.govGovernment
Climate Change - NASA Science
Backs: “Scientific Consensus. There is unequivocal evidence that Earth is warming at an unprecedented rate.”
2congress.govGovernment
Intergovernmental Panel on Climate Change: Sixth Assessment Report
Backs: “More than 99.9% of peer-reviewed scientific papers agree that climate change is mainly caused by humans, according to a new survey of 88,125 climate-related studies. What the IPCC Concludes. The Intergovernmental Panel on Climate Change (IPCC) was formed to provide internationally coordinated scientific assessments of…”
3nasa.govGovernment
New U.N. report: Humans responsible for climate change - NASA Science
Backs: “The Intergovernmental Panel on Climate Change (IPCC) was formed to provide internationally coordinated scientific assessments of climate change. Successive IPCC reports have strengthened the language on human responsibility: The IPCC report says there is 95 percent certainty that humans have caused most of the warming…”
4climate.govGovernment
Are humans causing or contributing to global warming?
Backs: “Yes, by increasing the abundance of greenhouse gases in the atmosphere, human activities are amplifying Earth’s natural greenhouse effect. Virtually all climate scientists agree that this increase in heat-trapping gases is the main reason for the 1.8°F (1.0°C) rise in global average temperature since the late…”