**2.1 Global warming vs. atmospheric CO2**

One of the key results in [10], reminded below, will be of great use in modelling with time the global warming. Based on the physics law of conservation of energy, this result states that the rise in global average temperature above the pre-industrial record is growing with the ratio *r* of CO2 concentration to the pre-industrial level. It can be seen as a generalization of the well-investigated climate response to doubling CO2 concentration [5, 18, 19].

$$
\Delta T(r) \approx \beta \frac{r-1}{r-k} \qquad (\beta \approx 5.84, k \approx -0.85) \tag{1}
$$
