Are humans responsible for climate change?

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

Yes, according to the overwhelming scientific evidence and consensus, humans are responsible for modern climate change - specifically the rapid warming observed since the mid-20th century.

1. The scientific conclusion is unequivocal

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

NASA states:

> Scientific evidence continues to show that human activities (primarily the human burning of fossil fuels) have warmed Earth’s surface and its ocean basins

The Intergovernmental Panel on Climate Change (IPCC), 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

A direct IPCC quote states:

> It is unequivocal that human influence has warmed the atmosphere, ocean and land

And:

> Since systematic scientific assessments began in the 1970s, the influence of human activity on the warming of the climate system has evolved from theory to established fact

The IPCC also reported:

> there is 95 percent certainty that humans have caused most of the warming of the planet's surface that has occurred since the 1950s

2. How humans cause it

Scientists attribute the warming to the human expansion of the greenhouse effect:

> 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

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

Specific mechanisms:

•Burning of fossil fuels like coal and oil has increased atmospheric CO2. The industrial activities that our modern civilization depends upon have raised atmospheric carbon dioxide levels by nearly 50% since 1750. This increase is due to human activities, because scientists can see a distinctive isotopic fingerprint.

•To a lesser extent, clearing of land for agriculture, industry, and other human activities has increased concentrations of greenhouse gases

•Five key greenhouse gases are carbon dioxide, nitrous oxide, methane, chlorofluorocarbons, and water vapor, with human-made emissions trapping and slowing heat loss to space

3. 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

Evidence includes:

> 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

> 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

4. Overwhelming scientific consensus

> Nearly all actively publishing climate scientists say humans are causing climate change

> 97% to 99.9% of climate scientists agree that climate change is happening and that human activity is the primary cause

Multiple statements from scientific bodies endorse this:

•American Geophysical Union: "it is extremely likely that human activities, especially emissions of greenhouse gases, are the dominant cause of the observed warming since the mid-20th century."

•American Association for the Advancement of Science: "about 97% of climate scientists have concluded that human-caused climate change is happening"

•Statement from 18 Scientific Associations: "rigorous scientific research demonstrates that the greenhouse gases emitted by human activities are the primary driver."

•U.S. Global Change Research Program (13 U.S. government departments and agencies): "Earth’s climate is now changing faster than at any point in the history of modern civilization, primarily as a result of human activities."

In summary, natural climate variability exists, but the rapid, unprecedented warming since the industrial era is principally caused by human activities, especially burning fossil fuels and emitting greenhouse gases that trap heat in the atmosphere.

Are humans responsible for climate change?

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