Are humans responsible for climate change?

Humans and climate change — I'll pull the latest scientific consensus on our role and the evidence behind it.

Yes, according to the overwhelming scientific evidence and consensus, humans are responsible for modern climate change — as the principal cause.

Scientific consensus is unequivocal

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

•There is a nearly unanimous scientific consensus that the climate is warming and that this is caused by human activities.

•As of 2019, agreement in recent literature reached over 99%.

•Nearly all actively publishing climate scientists (97–100%) 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.

The Intergovernmental Panel on Climate Change (IPCC), the UN body involving hundreds of scientists from countries worldwide, has strengthened its conclusions over time:

•In its Sixth Assessment Report (2021), its primary conclusion was that "[i]t is unequivocal that human influence has warmed the atmosphere, ocean, and land."

•The same report was described as stating that “it is unequivocal that human influence has warmed the atmosphere, ocean and land.”

•In its Sixth Assessment Report, the Intergovernmental Panel on Climate Change, composed of scientific experts from countries all over the world, concluded that it is unequivocal that the increase of CO2, methane, and nitrous oxide in the atmosphere over the industrial era is the result of human activities and that human influence is the principal driver of many changes observed across the atmosphere, ocean, cryosphere and biosphere.

> Scientists have known for some time, from multiple lines of evidence, that humans are changing Earth’s climate, primarily through greenhouse gas emissions.

How humans are causing it

Scientists attribute the global warming trend observed since the mid-20th century to the human expansion of the "greenhouse effect" — warming that results when the atmosphere traps heat radiating from Earth toward space.

•Increases in emissions of greenhouse gases such as carbon dioxide and methane due to human activity trap heat in the atmosphere, capturing outgoing radiation that would otherwise escape into space.

•Over the last century, burning of fossil fuels like coal and oil has increased the concentration of atmospheric carbon dioxide (CO2).

•The industrial activities that our modern civilization depends upon have raised atmospheric carbon dioxide levels by nearly 50% since 1750

Five key greenhouse gases are carbon dioxide, nitrous oxide, methane, chlorofluorocarbons, and water vapor. Of these, carbon dioxide, methane, nitrous oxide and chlorofluorocarbons are directly increased by human activities such as burning fossil fuels, deforestation, agriculture, landfills, livestock, and industrial production.

What about natural factors?

Natural factors do affect climate — such as changes in solar activity, volcanic eruptions, and internal variability like El Niño — but they cannot explain recent warming:

•Since 1750, the average amount of energy from the Sun either remained constant or decreased slightly

•Climate models that include solar irradiance changes can’t reproduce the observed temperature trend over the past century or more without including a rise in greenhouse gases.

•Although Earth’s temperature fluctuates naturally, human influence on climate has eclipsed the magnitude of natural temperature changes over the past 120 years.

•Natural influences on temperature—El Niño, solar variability, and volcanic aerosols—have varied approximately plus and minus 0.2° C (0.4° F), (averaging to about zero), while human influences have contributed roughly 0.8° C (1° F) of warming since 1889.

Quantitative attribution studies find humans responsible for essentially all of the observed warming since the mid-20th century:

•The IPCC’s implied best guess was that humans were responsible for around 110% of observed warming (ranging from 72% to 146%), with natural factors in isolation leading to a slight cooling over the past 50 years.

In short, the climate has changed naturally in the distant past, but the rapid warming since the industrial era — and especially since the 1950s — is dominated by human-caused greenhouse gas emissions.

Citations (2)

1nasa.govGovernment
Climate Change - NASA Science
Backs: “Scientific consensus is unequivocal. There is unequivocal evidence that Earth is warming at an unprecedented rate.”
2nasa.govGovernment
Causes - NASA Science
Backs: “The same report was described as stating that “it is unequivocal that human influence has warmed the atmosphere, ocean and land.”. In its Sixth Assessment Report, the Intergovernmental Panel on Climate Change, composed of scientific experts from countries all over the world, concluded that it is unequivocal that the…”