2.1 Observational constraints on the model

The physical model of SimClimat is based on physical equations. It differs from typical educational animations in which results are pre-recorded. All calculations are done once the simulation is launched, depending on the parameters chosen by the user. An infinity of simulations are possible.

However, SimClimat's physical model differs from true climate models (detailed in section 4) to the extent that many parameters in the equations have been adjusted so that the simulations yield realistic results. This parameter adjustment is necessary because the equations are very simplified. The equations are very simplified to limit the calculation time, in order to get simulation results in a few seconds.

The parameters have been adjusted to satisfy the following observational constraints:

• temperatures, $CO_{2}$ concentration, ice sheet latitude, sea level, and albedo for pre-industrial, present-day and last glacial maximum periods (Table 1);
• Extreme variations of orbital parameters induce temperature variations of the same order of magnitude as glacial-interglacial variations (10°C);
• Currently, water vapor and $CO_{2}$ respectively contribute to 60% and 40% of the natural greenhouse effect;
• The warming due to a doubling of $CO_{2}$ is 2.2°C when considering the effect of the water vapor but only of 1.2°C when neglecting this feedback ([Dufresne and Bony, 2008]).

Table 1: Table summarizing constraints for pre-industrial, present-day and last glacial maximum time periods.

Time period	Pre-industrial	Present-day	Last Glacial Maximum (-21 ka)
Temperature	14.5°C	15.5°C	10°C
$CO_{2}$	280 ppm	ppm	180 ppm
Sea level	-0.2 m	0 m	-130 m
Ice sheet latitude	-	60°	45°
Planetary albedo	-	0.33	-