2.4 Coupling the radiative equilibrium model with the other components

To calculate $T_{eq}$, we need the albedo $A$ and the greenhouse effect $G$. It is from these variables that the radiative model is coupled to the atmospheric composition, to the carbon cycle and to the ice sheets. All these coupled components are represented in figure 10.

Figure 10: Diagram illustrating how the different variables are computed in the model. In red: external forcing on the climate system. In blue: state variables.

2.4.1 Greenhouse effect

The greenhouse effect $G$ is decomposed into two components: the greenhouse effect associated with $CO_{2}$ ( $G_{CO_{2}}^{serre}$) and that associated with water vapor ( $G_{H_{2}O}^{serre}$) (section 5.2.1).

• The greenhouse effect associated with the water vapor is calculated according to the water vapor concentration $R_{H_{2}O}$ (section 5.2.3), which is calculated as a function of temperature (section 5.2.4).
• The greenhouse effect associated with $CO_{2}$ is calculated as a function of $CO_{2}$ concentration (section 5.2.2). This concentration is calculated from $CO_{2}$ sources and sinks (anthropogenic emissions, volcanism, continental alteration, biological storage, storage by the ocean) (section 5.3). The $CO_{2}$ solubility in the ocean is a function of temperature (5.3.2).

2.4.2 Albedo

Albedo $A$ is calculated as a function of ice sheet extent $phi_{g}$ (section 5.4.1). This extent is calculated as a function of temperature and of the insolation at 65°N $I$ (section  5.4.2). This insolation is determined by astronomical and orbital parameters.

2.4.3 Sea level

Sea levels depend both on temperature, through thermal expansion, and on ice sheet extent, which controls the available liquid water (section 5.5).