Are humans responsible for climate change?

Answering whether humans drive climate change — I'll gather the latest scientific consensus and evidence to explain.

Yes - according to the overwhelming scientific evidence, humans are the dominant cause of the rapid climate warming observed since the mid-20th century, though natural climate variability also exists.

What the major scientific assessments conclude

•The Intergovernmental Panel on Climate Change (IPCC), the global body that synthesizes peer-reviewed climate science, states in its Sixth Assessment Report (AR6, 2021):

> It is unequivocal that human influence has warmed the atmosphere, ocean and land. Widespread and rapid changes in the atmosphere, ocean, cryosphere and biosphere have occurred

•The report adds:

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

•In its Sixth Assessment Report, the IPCC 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

•Every major U.S. and international scientific academy, the IPCC, NASA and leading research organizations state that humans—primarily burning oil, gas and coal—are the dominant cause of recent warming

Why scientists attribute recent warming to humans

1.The greenhouse effect has been expanded by human emissions. 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

The greenhouse effect is essential to life on Earth, but human-made emissions in the atmosphere are trapping and slowing heat loss to space

Five key greenhouse gases are carbon dioxide, nitrous oxide, methane, chlorofluorocarbons, and water vapor

2.Concentrations have risen sharply due to human activity. Over the last century, burning of fossil fuels like coal and oil has increased the concentration of atmospheric carbon dioxide

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

3.Quantified human contribution to warming: The likely range of total human-caused global surface temperature increase from 1850–1900 to 2010–2019 is 0.8°C to 1.3°C, with a best estimate of 1.07°C. 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

This shows natural drivers (solar and volcanic activity) and internal variability are too small to explain observed warming.

4.Natural causes cannot explain current warming.

While the Sun has played a role in past climate changes, the evidence shows the current warming cannot be explained by the Sun

Specifically:

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

•If a more active Sun caused the warming, scientists would expect warmer temperatures in all layers of the atmosphere. Instead, they have observed a cooling in the upper atmosphere and a warming at the surface and lower parts of the atmosphere

•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

Scientific consensus

> Yes, the vast majority of actively publishing climate scientists – 97 percent – agree that humans are causing global warming and climate change

Multiple studies published in peer-reviewed journals show that 97 percent or more of actively publishing climate scientists agree: Climate-warming trends over the past century are extremely likely due to human activities. More recent literature surveys examining tens of thousands of papers report agreement levels from ~97% to greater than 99% among publishing climate scientists.

In short: Climate has changed naturally throughout Earth's history due to orbital, solar and volcanic factors, but the current rapid warming, ocean heating, ice loss, sea-level rise and increase in extreme heat events since about 1950 is unequivocally dominated by human emissions of CO2, methane, nitrous oxide and other greenhouse gases.

Citations (2)

1ipcc.chGovernment
Summary for Policymakers
Backs: “It is unequivocal that human influence has warmed the atmosphere, ocean and land. Widespread and rapid changes in the atmosphere, ocean, cryosphere and biosphere have occurred. The report adds: Observed increases in well-mixed greenhouse gas (GHG) concentrations since around 1750 are unequivocally caused by human…”
2nasa.govGovernment
Causes - NASA Science
Backs: “Observed increases in well-mixed greenhouse gas (GHG) concentrations since around 1750 are unequivocally caused by human activities. In its Sixth Assessment Report, the IPCC 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…”