An explorative evaluation of the climate debt

Résumé 0

The international process for tackling climate change endured several backslashes sincethe signing of the Paris Agreement in 2015. Issues around the respective responsibilitiesare not fully solved yet. The underlying question of how to share efforts in order to reacha Zero Net Emissions state remains largely unclear and the INDCs process has still todeliver a pathway for decarbonization.In the last years, the concept of global carbon budget has emerged as one of the mostdirect ways to materialize the constraint from the climate. It mainly relies on the idea thatonly a limited quantity of carbon dioxide can be released in the atmosphere if we want tostay below the 2°C temperature change threshold above pre-industrial levels and, ifpossible, below +1.5°C, as agreed at the Paris Conference in 2015. By comparing what isin our carbon budget to what is done to reduce the carbon footprint of societies, wecalculate a distance to the climate constraint. Expressed in euro this distance, called the“climate debt”, measure how much we avoid paying by delaying climate change mitigation. Using different rules for sharing the burden, acknowledging there is no negotiatednor consensual way to share it, we calculate this climate debt for main EU countries.The first step of the following work is to compute a carbon budget for both the EuropeanUnion and member countries mixing population based sharing (egalitarian) for EU andrest of world budget and emission based sharing (grandfathering) for EU countries. In asecond step, we determine how many years are left before these budgets are depleted atthe regional and national levels, which requires assumptions on the future emissionstrend. Combining these trends with assumptions on the abatement cost of remainingcarbon dioxide emissions after the depletion date allows us to evaluate the “climatedebt”. More precisely, the “climate debt” is the amount of money that will have to beinvested or paid by countries for them not to exceed their carbon budget.This work led us to three key policy insights. First, there are few years left for major European countries before exhausting their carbon budget under the +2°C target. As for the+1.5°C target, carbon budgets are exhausted for EU main countries, which are thusrunning excessive climate deficits. Secondly, the carbon debt should be considered asone of the major issues of the decades to come since in the baseline scenario it representsabout 50% of the EU GDP to stay below +2°C (120% for staying below +1.5°C). Thirdly,the results of the estimation of this carbon debt are subject to numerous moral, ethicaland technical assumptions that should motivate further and urgent investigations on thissubject, critical to climate change mitigation, from both state bodies and independentresearch institutes.