FACT BRIEF

Is there empirical evidence for human-caused global warming?

Thursday, July 8, 2021

By John Cook

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YES

The greenhouse effect—that atmospheric gases such as carbon dioxide warm the planet by trapping and reradiating heat—was first demonstrated using experiments in 1859. Without greenhouse gases, Earth would be nearly 60 degrees Fahrenheit (33°C) cooler.

After remaining relatively stable for 800,000 years, atmospheric CO2 spiked since the Industrial Revolution to 416 parts per million as of February 2021— a nearly 50% increase from preindustrial times.

We know this increase is from burning fossil fuels. Fossil fuel carbon does not contain the carbon 14 isotope. The recent relative decrease in atmospheric carbon 14 betrays a fossil fuel “fingerprint” in the CO2 spike.

At the same time, heat energy radiating out to space has decreased while heat energy reradiating downward to Earth—specifically, heat energy at the same wavelength that CO2 is known to trap—has increased, implying a strengthening anthropogenic greenhouse effect.

See a full discussion of this at Skeptical Science

This fact brief is responsive to conversations such as this one.

Sources

American Institute of Physics The carbon dioxide greenhouse effect

NASA Vital Signs: Carbon dioxide measurements

Reuters CO2 levels to breach 50% rise from pre-industrial era in 2021 - Met Office

National Oceanic and Atmospheric Administration The Basics: Isotopic Fingerprints

NASA Earth Observatory: Climate and Earth’s energy budget

Columbia Climate School How exactly does carbon dioxide cause global warming?

ABOUT THE CONTRIBUTOR

Skeptical Science

Skeptical Science is a non-profit science education organization. Our goal is to remove a roadblock to climate action by building public resilience against climate misinformation. We achieve this by publishing debunking of climate myths as well as providing resources for educators, communicators, scientists, and the general public. Skeptical Science was founded and is led by John Cook, a Senior Research Fellow with the Melbourne Centre for Behaviour Change at the University of Melbourne.

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