New Research Says Doubling CO2 Leads To A ‘Sometimes’ Negative Greenhouse Effect

“Negative TOA [top of atmosphere] forcing of CO2 increase also happens outside of Antarctica. The Arctic sometimes exhibits strong negative CO2 forcing. This phenomenon even occurs in the tropics and mid-latitudes…” – Chen et al., 2024

It has previously been reported that as CO2 increases from 380 ppm to 1000 ppm, the CO2 greenhouse effect is negative (-2.9 W/m²) over Antarctica, or that CO2 “increases radiative cooling” there (Schmithüsen et al., 2015).

Also, the CO2 greenhouse effect is as “comparatively weak” (hovering around 0 W/m²) over Greenland as it is over Antarctica, but it is not negative there, as it is “invariably” above 0 W/m² in the Arctic. In other words, there is no such thing as a CO2-enhanced “polar amplification” at locations where it is commonly claimed CO2 is causing catastrophic ice melt.

Image Source: Schmithüsen et al., 2015

But new research (Chen et al., 2024) indicates when CO2 increases from 380 to 760 ppm the negative (below 0 W/m²) greenhouse effect of CO2 can not only be found over Antarctica, but “sometimes” in the Arctic (Greenland especially), the tropics, and mid-latitudes as well.

The bar graphs and colorized chart in the paper show that as CO2 doubles (760 ppm) it only produces a radiative forcing differential ranging between -1.5 W/m² to about +3 W/m².

In contrast, the authors identify cloud radiative forcing (CRE, cloud radiative effect) contributing ~120 W/m² (50-190 W/m²) to greenhouse effect enhancement. In other words, the greenhouse effect of clouds is two orders of magnitude larger than from the greenhouse effect from doubled CO2.

This is consistent with the assessment that CO2 must be increased 100-fold (to ~40,000 ppm) to begin to revival the greenhouse effect of clouds (Ramanathan et al., 1989). Given analyses like these, it is rather puzzling that it is believed CO2 is the climate driver.

Image Source: Ramanathan et al., 1989