This figure was calculated by researchers from the University of Geneva on behalf of the Swiss Federal Office for the Environment (FOEN) in 2015 and based on the total Swiss budget for CO₂. This was then equally divided among all Swiss residents up until 2100.
Since this budget has already been exceeded for several years, this means that the CO₂ budget for the future is effectively even lower. Basically this means: The later the target of net zero emissions is reached, the higher the negative emissions will need to be later (see: What does “zero net emission” mean?).
The budget approach shows how compensation mechanisms work as a bridging technology: If you offset a flight, these emissions do not disappear, but emissions are prevented to the same extent elsewhere. The balance sheet remains balanced and so does the budget. However, it is the goal of myclimate that this voluntary offsetting becomes superfluous: Through clean technological innovation and a binding pricing of CO2 emissions in every product and service.
Source: Dao, et al. (2015)