All the previous climate changes show how sensitive climate is to increases in atmospheric CO2. In fact they prove that humans can significantly influence climate by industrial CO2 emissions.
Increase in atmospheric greenhouse gases means that the Earth re-radiates less energy into the space than it receives from the Sun. That leads to the Earth’s energy imbalance, which we measure as the so called radiative forcing, expressed as W/m2.
How many degrees will the global temperature change at a specific change in radiative forcing? That depends on the planet’s climate sensitivity, defined as the change in temperature in response to doubled concentration of CO2 in the atmosphere after the radiative balance is restored, which may well take centuries. Multiple studies using various methods suggest the value is 2-4.5°C, with the most probable being the proximity of 3°C.
Isn’t it ironic that when sceptics refer to past climate changes, they in fact deliver evidence on how sensitive climate is and that positive feedback kicks in in climate change.
High climate sensitivity means that increasing concentration of atmospheric CO2 contributes to climate warming. Today it is the humans who increase the concentration of CO2.
