2°C: the history of a policy-science nexus

Un article consacré à l'émergence puis l'avènement du concept de « 2°C » comme objectif de limite de l'augmentation des températures d'ici 2100 dans les négociations internationales.

Parmi les questions abordées par cet article figurent l'origine d'un concept au carrefour de la science et de la décision politique, son impact en termes d'ambitions des politiques climatiques, et sa capacité d'influence sur le déroulement des négociations internationales sur le changement climatique.

Points clés [en anglais] :

NO CLEAR ORIGIN FOR THE 2°C TARGET
An analysis of the first appearance of the objective to limit temperature rise to 2°C shows that it has no clear origin and that its adoption is due neither to compelling scientific evidence nor to the negotiators’ informed choice based on scientific date. Before the UNFCCC negotiations seized on this value, 2°C was already used as a marker to concurrently address scientific, economic and political apprehensions about climate change.

The 2°C as A SCIENCE-POLICY INTERFACE
The growing presence of the 2°C target resulted from the joint efforts of the scientific and political spheres to give structure to the debate, each enriching and exchanging with the other. This progression gave the 2°C target a meaning that varied according to the different contexts in which it was used. It thus became the interface between mitigation and adaptation, between scientific and political discourses and between the interests of the Parties.

ADOPTION OF THE 2°C: A WEAKENING OF AMBITIONS?
Discussions on the long-term objective sifted through several formulations for targets. Among these, the stabilisation level for greenhouse gas concentrations was used as a benchmark for quite some time. Prior to Copenhagen, the debate focused on the choice of a set of parameters seen as being mechanically interlinked in order to bring actions into line. However, the Parties were only able to agree on the 2°C, which was not only the most readable formulation but also the vaguest and the least directly binding.

A RAPPELLING ROPE FOR THE NEGOTIATIONS
The 2°C value has a precise scientific definition that makes it suitable for use as a rappelling rope and the measure of a level of ambition, with certain implications in terms of actions. It brings the global, long-term dimension of climate change down to a scale that is readable for policymakers, at the same time retaining the flexibility needed to integrate both scientific and political uncertainties. It is no longer simply a scientific indicator that been translated into policy terms, but a fully political target whose scope will be guaranteed by scientific evaluation.