Fact brief – Does increasing CO2 have a noticeable effect?

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Posted on 14 October 2025 by Sue Bin Park

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Does increasing CO₂ have a noticeable effect?

The warming effect of increasing atmospheric CO₂ is well-established physics, confirmed by direct observation.

Experiments in the 1800s by Fourier, Foote, and Tyndall demonstrated how CO₂ absorbs infrared radiation — the heat Earth emits back toward space — and re-radiates some downward, keeping the planet warmer. In 1896, Arrhenius calculated that doubling CO₂ would raise global temperatures by 5-6°C (9-10.8°F) . Modern estimates hover around 3°C (5.4°F), with an upper range near 4.5°C (8.1°F).

Today, satellite and surface instruments detect less heat escaping to space and more returning to Earth at CO₂’s specific wavelengths, exactly as predicted. Global average temperature is now about 1.28°C (2.3°F) above the preindustrial average, matching an increase from 280 ppm to 420 ppm.

While water vapor is the most abundant greenhouse gas, it cannot increase until temperatures do.

Far from negligible, human-made CO₂ is the main factor controlling Earth’s temperature today.

Go to full rebuttal on Skeptical Science or to the fact brief on Gigafact^[4][5]

This fact brief is responsive to quotes such as this one^[6].

Sources

JSTOR Daily How 19th-Century Scientists Predicted Global Warming^[7]

Endeavour CO2, the greenhouse effect and global warming: from the pioneering work of Arrhenius and Callendar to today’s Earth System Models^[8]

Carbon Brief Explainer: How scientists estimate ‘climate sensitivity’^[9]

NASA Global Temperature^[10]

NOAA Climate change: atmospheric carbon dioxide^[11]

Environmental Defense Fund 9 ways we know humans caused climate change^[12]

EPA Causes of Climate Change^[13]

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About fact briefs published on Gigafact

Fact briefs are short, credibly sourced summaries that offer “yes/no” answers in response to claims found online. They rely on publicly available, often primary source data and documents. Fact briefs are created by contributors to Gigafact^[15] — a nonprofit project looking to expand participation in fact-checking and protect the democratic process. See all of our published fact briefs here^[16].