Are humans responsible for climate change?

Are humans driving today's climate change? I'll pull the latest scientific consensus to answer.

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

1. Scientific consensus

Multiple independent efforts to quantify expert agreement show overwhelming consensus that recent warming is anthropogenic:

> Scientific consensus identifying humans as primarily responsible for climate change ... Today, 97% to 99.9% of climate scientists agree that climate change is happening and that human activity is the primary cause

Other analyses put the agreement similarly high:

> Multiple independent analyses ... put agreement that humans are causing recent warming at roughly 97% or higher, with ... consensus estimates above 99%

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

NASA summarizes the evidence as:

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

2. What the IPCC says

The Intergovernmental Panel on Climate Change (IPCC), which assesses over 14,000 peer-reviewed studies by 234 scientists from over 65 countries, has strengthened its conclusion in every assessment:

The report describes this as a statement of fact:

> "So it is a statement of fact, we cannot be any more certain; it is unequivocal and indisputable that humans are warming the planet"

AR6 estimates a likely human contribution of 0.8 to 1.3 degrees Celsius to global mean temperature since the late 1800s

3. How we know it is human, not natural

Climate scientists distinguish natural forcings from anthropogenic forcings:

> Natural climate forcings include changes in the sun's energy output, regular changes in Earth's orbital cycle, and large volcanic eruptions... Human-caused, or anthropogenic climate forcings include emissions of heat-trapping gases

Evidence shows natural factors cannot explain observed warming:

> While there are natural factors that affect the Earth's climate, the combined influence of volcanoes and changes in solar activity would have resulted in cooling rather than warming over the past 50 years.

> In general, climate changes prior to the Industrial Revolution in the 1700s can be explained by natural causes, such as changes in solar energy, volcanic eruptions, and natural changes in greenhouse gas ... Recent climate changes, however, cannot be explained by natural causes alone

And:

> Research indicates that natural causes do not explain most observed warming, especially warming since the mid-20th century. Rather, it is extremely likely that human activities have been the dominant cause of that warming

Volcanoes, often cited as a natural alternative, emit far less CO2:

> On average, volcanoes emit between 130 and 230 million tonnes of carbon dioxide per year. By burning fossil fuels, people release in excess of 100 times more, about 26 billion tonnes

4. Mechanism: Greenhouse gases and energy balance

Humans have artificially raised greenhouse gas concentrations:

> over the past 250 years, humans have been artificially raising the concentration of greenhouse gases in the atmosphere at an ever-increasing rate, mostly by burning fossil fuels... Since the Industrial Revolution began in about 1750, carbon dioxide levels have increased nearly 38 percent ... and methane levels have increased 148 percent

Direct satellite observations now confirm the theory:

> Climate modelling predicts that human activities are causing the release of greenhouse gases and aerosols that are affecting Earth's energy budget. Now, a NASA study has confirmed these predictions with direct observations for the first time: radiative forcings are increasing due to human actions

NASA describes this as direct evidence:

> "There is direct evidence that human activities are causing changes in the Earth's energy budget."

In summary, natural climate variability exists and drove changes in the distant past, but the rapid warming since the mid-20th century, the increase in ocean heat content, glacier retreat, and the increase in hot extremes are unequivocally linked to human emissions of CO2, methane, and other heat-trapping gases from burning fossil fuels and deforestation.