# Contents

## Idea

A plan from the German German Advisory Council on Global Change (WBGU). Right now this page is just clips from the “Summary for policy makers” in the report. This picture shows the idea and one example where the countries have been grouped into three aggregate per capita per year $CO_2$ emissions :

## Details

### Problem

From the executive summary:

The vast majority of scientists now agree that if global warming exceeds a mean temperature of 2 °C it will lead to dangerous, irreversible and practically uncontrollable consequences for both nature and mankind.

### Approach

From the executive summary:

The budget approach advocated by the WBGU will enable not only the reduction targets of the industrialised countries up to 2020 to be based upon a systematic foundation, but also the increasing decarbonization commitments that will have to be achieved by the newly industrializing and developing countries. This can lead to the growth of common understanding among all signatory states concerning the medium- and long-term actions necessary in order to implement the UNFCCC. The climate policy solution proposed by WBGU also has other merits: it creates a considerable degree of inter-temporal and inter-regional flexibility.

The solution makes it possible to dispose largely without restrictions over national greenhouse gas budgets during the long budget time period, based on a small number of rules that ensure compliance with the national and global decarbonization targets up to the middle of the 21st century. The intensive trading of emission allowances between all countries should be explicitly possible. This flexibility and the taking into account of

historical responsibilities give rise to various ways of financing mitigation and adaptation measures and promoting the transfer of technology between the industrialized and the developing countries.

### Mathematics

Box five in the report:

The key parameter is the global CO2 emissions budget from fossil sources $C_glob(p)$, i.e. the maximum emission from fossil sources which may be released/produced within a specific period $T1$ to $T2$ if the 2 °C guard rail is tobe obeyed with probability $p$. Once $p$ has been defined (based on precautionary factors), then $C_glob(p)$ can be determined from model studies within the bounds of specific uncertainties (Meinshausen et al., 2009). The global emission pathway $E_glob(t)$ must be compatible with this constraint, i.e. it must fulfil the following equation.

Of course, ‘under-utilization’ of the resource ‘atmosphere’ is also conceivable, but it can be assumed that, in reality, the leeway for global emissions will be fully exhausted. It is important to bear in mind that equation 1 only fixes the area below the global emissions curve but otherwise allows full freedom to determine the reduction schedule.

$\int_{T1}^{T2}E_glob(t)dt=C_glob(p)(1)$

The national emissions budget $C_nat$ is the total amount of $CO_2$ that a specific country is allowed to emit in the time period $T1-T2$. It is calculated as a proportion of the global emissions budget $C_glob(p)$, based on the relative demographic weight of the given country in the demographic reference year $T_M$. The coefficient is therefore the quotient from the national population figure $M_nat(T_M)$ at time $T_M$ and total world population $M_glob(T_M)$ at the same point in time.

A country’s emission pathway $E_nat(t)$ must thus bemanaged in such a way that it matches the allocated budget:

Equation 2 can be regarded, to some extent, as the global ‘climate formula’ within the budget approach’s philosophy.

$\int_{T1}^{T2}E_nat(t)dt=C_nat(p)=C_glob(p)\frac{M_nat(t_m)}{M_glob(t_m)}(2)$

## References

• Solving the climate dilemma: a budget approach available here on WBGU

category: plans