Choosing a Stabilization Target for Co2

The choice of stabilization target for CO2 concentration depends on the following: what is considered to be ‘dangerous anthropogenic interference with the climate system’; the forcings that might arise from non-CO2 gases; and the climate sensitivity. These three factors are specified here probabilistically, as probability density functions (pdfs), and combined to produce a pdf for the CO2 concentration target. There is a probability of 17% that the stabilization target should be less than the present level, and the median target is 536 ppm. The effects of reducing the emissions of non-CO2 gases and/or implementing adaptation strategies are considered probabilistically and shown to alter these figures significantly.