2°C more. How bad is it ?
There is also a difference between land and ocean. The average increase of +2°C hides a stronger increase (around +3°C) on land.
The Humidex is the scale that combines temperature and humidity to describe conditions that are difficult for humans to live with.
These three articles discuss the effect of temperature change on human populations:
- Global risk of deadly heat, in Nature Climate Change. 2017.
- The emergence of heat and humidity too severe for human tolerance, in Sciences Advances. 2020.
- Future of the human climate niche, in PNAS. 2020
20,000 years ago, the Earth experienced its last ice age. The ice caps that covered Scandinavia melted and raised sea levels by 125 meters, making England an island, and above all, Europe a habitable zone.
It is estimated that these climatic, and therefore agricultural, conditions increased the population from 300,000 people 30,000 years ago to 150,000 people, 20,000 years ago. Before rising to 420,000, when conditions became milder 10,000 years later.
It is this same reason that explains why every tenth of a degree counts. Because each additional tenth of a degree will see its consequences much stronger than the previous tenth.
We say here that the effects are not linear, that there is no proportionality, since a given increase in temperature does not imply the same effects, whether it starts at 15°C, 18°C or 31°C.
Also, past variations have first seen the temperature rise (or fall) and then be followed by CO2, unlike the current period for which it is CO2 that is responsible for temperature variations.
Thus, it is impossible to deduce anything from past variations and changes, except that they have all been at the origin of brutal changes and have profoundly modified the conditions of life on Earth.