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.