The concepts of equity and justice

Flow-Based Approaches

These are approaches that allocate targets to countries based on the annual flow of emissions (as opposed to the cumulative stock of emissions). Two prominent types of flow based approaches are:

1. 2.1

   Contract and Convergence Approach

2. 2.2

   Burden Sharing Approach

Each of these approaches is discussed below:

Contract and Convergence Approach

The contract and convergence (C&C) approach to mitigation is one of the oldest methods within this set of approaches. In this approach, equity is operationalised by considering the equality of per capita emission flows. What this means is that developed nations must reduce, and developing nations can increase their per capita emissions flows, and thus converge to a common target at a predetermined year. Some variants of this method utilise a country’s per capita GDP or other economic criteria to determine the reduction rates in the annual emission flows. Such flow-based understanding is common and seen within Nationally Determined Contributions (NDCs) of developed countries, targets in the Kyoto Protocol, among others. But as easy as they are to formulate or implement, these approaches have 3 fundamental problems:

• They do not include historical emissions and by their own definition consider themselves to be ‘forward looking’ in nature.
• The flow trajectories have implied cumulative emissions associated with them which are ignored. This may mean that flow-based targets of the developed nations allow them to capture more carbon space into the future even though they have exceeded their fair share in the past. This is unfair to historically low emitting nations.
• There are versions of C&C which have an arbitrary clause that developing nations cannot exceed the emissions of developed countries. This limit on developing country emissions may severely restrict them from utilizing resources for their development.

Burden Sharing Approach

The burden sharing or ‘Bending the curve’ approach considers the mitigation burden to be the effort required to move from a flow-based baseline emissions trajectory to a stabilization trajectory. The baseline scenarios are typically constructed using results from Integrated Assessment Models. The steps to distribute the mitigation burden are varied.

One approach that comes closest to including equity is the Greenhouse Development Rights approach or its newer version, the Equity Reference Framework. This allocates emissions rights to countries based on the proportion of the country’s population living below the poverty line. CBDR is implemented by allocating a share of the burden, i.e., the difference between the business-as-usual trajectory and the stabilisation trajectory, to countries, based on a formula. This formula includes both responsibility (in terms of cumulative emissions from a base year, or per capita emissions) and capability (i.e., per capita GDP, non-income HDI).

The advantages of this approach include:

• The explicit acknowledgment of both responsibility and capability, the two key elements of Article 3.1 of the Convention.
• It uses cumulative historical emissions as an indicator of responsibility, but the actual calculations of mitigation burden are emissions flow based. This makes it amenable to the five-year review process that is part of the Paris Agreement’s Article 14 on the Global Stock Take.
• It factors in equity without having to invoke ‘entitlements’ which makes it potentially acceptable to all parties, especially the developed countries.

The drawbacks of this approach are the following:

• The mitigation burden is the difference between the global stabilization trajectory and the baseline trajectory for each region. For every temperature target there is a range of associated cumulative emissions and so multiple stabilisation trajectories are possible for the same value of the carbon budget. However, only one such trajectory is chosen in this approach. This choice influences the estimation of mitigation burdens. Further, baseline trajectories are highly speculative. For instance, they are constructed based on assumptions that do not include current trajectories (encompassing stated mitigation policies of nations). Additionally, for developing countries with rapidly changing economic structures there is a much higher chance that any given baseline will not hold for the long term. This implies that mitigation burdens that are calculated using both these two key criteria are highly uncertain.
• Mitigation burden is calculated progressively. So, any economic growth will automatically lead to an increase in the share of the mitigation burden that a country has to undertake. In this approach ‘fair share’ is not the ‘fair share of the carbon space’, but a ‘fair share of the mitigation burden’. So progressive estimation of the burden means that with economic growth the share of the carbon space for the country changes, and hence any steps taken by the country to improve their circumstances will be penalized with a higher mitigation burden. This is the cost of not considering an explicit allocation of entitlements.

Cumulative Emissions Based Approaches

As the name suggests, cumulative emissions based approaches account for cumulative emissions and historical emissions. The carbon budget approach is an example of cumulative emissions. In this approach, the total global carbon budget is first calculated for a given temperature target. The estimation of the total carbon budget for a given temperature rise for a given probability includes the sum of the past and future emissions. The past emissions are considered to be emissions that occurred between 1850 and 2019. Future emissions refer to what is left to be emitted from the current year till net zero emissions are achieved. After accounting for emissions that have already taken place, it divides the remaining carbon budget available for the future based on some criteria.

There are different ways to divide the remaining carbon budget. One way is to first define entitlements of all nations using the total carbon budget from 1850 till net zero emissions are achieved, and distribute this space equally among nations based on some equity parameters, e.g., per capita share of the total. Given the entitlements of each nation, the nations which have exceeded their share must find ways to remove carbon and nations which have been low emitters can use their share to develop. Another way to divide the carbon space would be to completely ignore past emissions and only decide entitlements based on equitable distribution of future emissions. This would be akin to negating all historical responsibility of past emitters. Yet another method is to combine these approaches and include historical responsibility to estimate entitlements to only the remaining carbon space.

The entitlement of a nation in this approach is the quantum of emissions it can emit till it reaches net-zero emissions. This means that there are multiple possible pathways to reach zero emissions while limiting the total cumulative emissions. This is especially useful for developing nations as they may choose when and how to reduce their emissions.

The advantages of this approach include:

• The mitigation burden estimates, i.e., that the remaining carbon budget, is independent of baseline trajectories of speculative nature.
• There is no requirement of one emissions trajectory as there are many possible emissions trajectories that result in the same cumulative emissions for a particular value of the carbon budget.
• The upfront estimation of the entitlements removes the issue of penalising developing countries for improving their national circumstances.

A criticism of the carbon budgets approach is that monitoring cumulative emissions is more difficult than monitoring annual emission flows. But as multiple possible emissions trajectories can be constructed for any given budget allocation, this issue can be addressed by mapping the actual emissions against a set of trajectories compatible with the budget to determine whether the country is on track to remain within its allocated share.