How Increased CO2 Warms the Earth-Two Contexts for the Greenhouse Gas Effect

The widespread explanations of the greenhouse effect taught to millions of schoolchildren are misleading. The objective of this work is to clarify how increasing CO2 produces warming in current times. It is found that there are two contexts for the greenhouse gas effect. In one context, the fundamental greenhouse gas effect, one imagines a dry Earth starting with no water or CO2 and adding water and CO2. This leads to the familiar “thermal blanket” that strongly inhibits IR transmission from the Earth to the atmosphere. The Earth is much warmer with H2O and CO2. In the other context, the current greenhouse gas effect, CO2 is added to the current atmosphere. The thermal blanket on IR radiation hardly changes. But the surface loses energy primarily by evaporation and thermals. Increased CO2 in the upper atmosphere carries IR radiation to higher altitudes. The Earth radiates to space at higher altitudes where it is cooler, and the Earth is less able to shed energy. The Earth warms to restore the energy balance. The “thermal blanket” is mainly irrelevant to the current greenhouse gas effect. It is concluded that almost all discussions of the greenhouse effect are based on the fundamental greenhouse gas effect, which is a hypothetical construct, while the current greenhouse gas effect is what is happening now in the real world. Adding CO2 does not add much to a “thermal blanket” but instead, drives emission from the Earth to higher, cooler altitudes.