Climate sensitivity calculator

Enter a value for CO2 level, a value for climate sensitivity, and click "Submit".

The output shows how much the global temperature is expected to rise, compared to the preindustrial level of 1850.
The preindustrial CO2 level was 280 ppm.
The current CO2 level is 400 ppm.
The current global temperature increase since 1850 is approximately 1.0 degree Celsius.

Enter CO2 level: valid range: 200 to 2000 ppm.
Enter climate sensitivity: Valid range 0 to 7 Celsius, see explanation below.

What is climate sensitivity?

The Climate sensitivity is a measure of how much the average global temperatures are expected to rise if we have a doubling in the atmospheric CO2 content.

Although we know that the CO2 level has increased from 280 ppm to 400 ppm, and that global average temperature has increased by 1.0 Celsius in the same period, we don't know how exactly much of it that is due to CO2 increase.

We know from historical data that the global temperatures can change due to natural variations.

If some of the current temperature increase is due to natural variations, the climate sensitivity may be lower than expected.
However, natural variability may also have caused the current global temperature to be lower than what the climate effect of increased CO2 level otherwise would have brought. If that is the case, the climate sensitivity may be higher than expected.

The Intergovernmental Panel on Climate Change (IPCC) says in their fifth assessment report (AR5) that the equilibrium climate sensitivity is likely between 1.5 and 4.5 Celsius. Furthermore they specify that by "likely" they mean at least 66 percent likelihood.

AR5 also assess that the equilibrium climate sensitivity is by 95% likelihood within the interval 1 to 6 degrees Celsius. This means that it is a high degree of uncertainty of how much the temperature will increase because of CO2 emissions.
This has a huge impact on how high the CO2 level can be allowed to increase if we shall keep the temperature increase below the target of two degrees Celsius.

If the climate sensitivity is 6 Celsius, the CO2 level has to be held below 396 ppm
If the climate sensitivity is 3 Celsius, the CO2 level has to be held below 444 ppm
If the climate sensitivity is as low as 1 Celsius, the CO2 level can rise to 1120 ppm before the temperature rise 2 degrees Celsius.

Read more about climate sensitivity in AR5 Summary for policymakers page 16