Climate science has calculated that from 1 January 2020, there is “room” for 300 billion tonnes more CO2 in the atmosphere . This is called the CO2 budget.
In addition, there is also “space” for a quantity of other greenhouse gases corresponding to approx. 88 billion tonnes of CO2 equivalents  (CO2e).
The sum of the two, which can be called the total greenhouse gas budget, was therefore 388 billion tonnes CO2e applicable from 2020.
Distribution of greenhouse gas budget – by population
The global greenhouse gas budget must somehow be distributed to the various countries and the EU.
Several principles of distribution exist. Here the distribution is based on a principle in which all people on earth have the right to an equal share of the present total greenhouse gas budget.
The EU-population thus amounts to approx. 5.8 % of the World’s population.
The EU27 can then be allocated 5.8% of the World’s greenhouse gas budget, which corresponds to approx. 22,447 million tonnes CO2e per January 1, 2020.
Emissions for 2020 have not yet been finally calculated, but in 2019 it was 3.6 billion tonnes CO2e .
If you continue with the same level of emissions as in 2019, the greenhouse gas budget will have been used up already in the year 2026.
One must put together the annual reductions in a way so that the greenhouse gas budget is not exceeded. This can be done in many ways, which is also called reduction paths.
One way is to reduce CO2e emissions by a fixed amount each year.
Choosing this way, it is necessary to reduce by 275 million tonnes of CO2e every single year from 2021 until and including the year 2032, when the greenhouse gas budget has largely been used.
From the year 2033, CO2e emissions must be zero.
Reduction path and ongoing evaluation
In the figure below, the reduction path described previously is illustrated
It is important to evaluate on an ongoing basis whether the planned reductions are achieved.
If the necessary reduction of 275 million tonnes CO2e in 2021 is not achieved, then we must increase the reductions in the coming years so that the greenhouse gas budget is not exceeded.
The reduction path and the remaining greenhouse gas budget must thus be revised at least once a year to reflect the real situation.
Percentage targets are a wrong measure
In the climate issue, success criteria are not determined by percentage targets for reductions in arbitrary years, but by the total emissions of greenhouse gases in a given time interval.
Therefore, the principled method of letting percentage targets be success criteria is wrong.
“Fit for 55” has used a percentage target of 55% reduction compared to 1990. The percentage target is completely misleading and in no way ensures coherence between the necessary action required by climate science and the results achieved.
Unfortunately, this incorrect method is also used in most other contexts, e.g., in climate acts and in municipal climate plans.
One has failed catastrophically if e.g., succeeding in achieving a CO2e reduction of 55% in 2030 (compared to a reference year) or net emissions in 2050, but that on the way more greenhouse gases have been emitted than there was room for in the budget.
The greenhouse gas budget is the right measure
In other words, the success criteria for climate efforts must be based on whether the road or path you take towards a given year complies with the greenhouse gas budget.
We must not make the mistake of setting static targets for a greenhouse gas reduction of x% in specific years. Instead, we must keep the necessary climate efforts up against dynamic greenhouse gas budgets, where the budget is continuously adjusted according to how much we emit and what the latest climate science dictates.
In the table below, the greenhouse gas budget is calculated on 1/1 and 31/12 for each year in the period 2020-2035 for the previously mentioned reduction path, where emissions are reduced by a fixed amount of 275 million. tonnes CO2e each year.
The greenhouse gas budget for EU27 was approx. 22.5 billion tonnes CO2e per January 1, 2020.
In 2019, EU27 emitted just over 3.6 billion tonnes CO2e, and if continuing with the same level of emissions as in 2019, the greenhouse gas budget will have been used up already by the year 2026.
In the climate issue, success criteria are not determined by percentage targets for reductions in arbitrary years, but by the total emissions of greenhouse gases in a given time interval
The success criteria for climate efforts must be based on whether the road or path you take towards a given year complies with the greenhouse gas budget.
There are several options for planning a reduction path so that the greenhouse gas budget is not exceeded.
This article describes a path where CO2e emissions are reduced by a fixed amount each year.
For that reduction path, it is necessary to reduce by 275 million tonnes of CO2e every year from 2021 until the year 2032, when the greenhouse gas budget is largely exhausted.
From the year 2033 CO2e emissions must be zero.
 IPCC, 2021: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson-Delmotte, V., P. Zhai, A. Pirani, S. L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M. I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J. B. R. Matthews, T. K. Maycock, T. Waterfield, O. Yelekçi, R. Yu and B. Zhou (eds.)]. Cambridge University Press. In Press.
https://www.ipcc.ch/report/ar6/wg1/#FullReport. Budget with an 83 % probability for staying below a global average temperature increase of 1.5°C.
 In a scenario, where other grenhouse gasses (e.g., methane) represent the same share of total greenhouse gases throughout the period. Increasing the share of other greenhouse gases reduces the CO2-budget and vice versa.