The figures of the negotiations: 2 °C

In July, during the Major Economies Forum (MEF) at the L’Aquila Summit, the Heads of State from the 17 highest emitting countries agreed to make the target of limiting global warming to +2 °C the beacon for international emissions reduction efforts. There are, in principle, several indicators that could serve as long-term markers: an impact level, a rise in temperatures, a GHG concentration, a level of cumulative emissions (over a period), or a reduction in emissions (by a certain date in relation to another). So why was this particular indicator chosen and, in particular, why was 2 °C chosen? And what are the questions that this choice raises today in international negotiations?

When its second report was published, the IPCC was criticised because its presentation of the risks linked to climate change was deemed unclear. For its third report, the IPCC therefore established a battery of global – and thus unavoidably simplified – indicators of the risks associated with global warming: risks for unique ecosystems, risks of extreme climate events, risks of climate discontinuities, the distribution of impacts and the aggregation of impacts. At 2 °C, most of the indicators showed a moderate risk, and at 3 °C a high risk. The fourth IPCC report upwardly revised all of these risks, and at 2 °C, almost all of these indicators now show a high risk.

Certain countries, including the Member States of the European Union, and environmental pressure groups therefore chose to make this target of limiting global warming to +2 °C the beacon for international emissions reduction efforts. This was a specific choice. They refused to follow the cost-benefit approach, which in theory makes it possible to determine the emissions reduction level that equalises the marginal cost of damage and of emissions reductions. Instead, they chose to build a political consensus on a temperature rise above which the risk of damage is considered intolerable. The Heads of State that met at the MEF summit finally gave their support to this position, after intense negotiations. The emerging countries in particular eventually exchanged short-term individual commitments for this long-term global target.

Based on this objective of limiting global warming to +2 °C, even if the correspondence is not exact, a remaining carbon budget is calculated for the 2009-2050 period. Given the failure of policies in developed countries since the UNFCCC negotiations in Rio in 1992, the mathematics have become implacable. This carbon budget constrains developed countries. According to the figures, they must make rapid and massive reductions in their emissions in order to ensure a 25 to 40% cut by 2020 and an 80% cut by 2050 in relation to 1990. But it also constrains emerging countries, which must rapidly decouple their economic growth from that of their emissions in order to halve these by 2050 in relation to 1990.

For all concerned, there are considerable constraints, and without necessarily being impossible to overcome, they nevertheless raise some serious problems. Moreover, scientific findings are increasingly pessimistic as to the chances of limiting global warming to +2 °C. Because of this, some are tempted to reconsider this target. Now is not the time to ease the pressure.

The MEF summit has set a positive trend in motion. The target of limiting global warming to 2 °C is for the time being the only truly political point of reference in the negotiations. It could potentially succeed in raising the level of collective ambition. And if this long-term objective is reconsidered, there will undoubtedly be a slackening of efforts in the short term. However, the absolutely crucial factor is the level of emissions reductions in 2030. Rather than focusing only on 2020 and 2050, negotiators should in fact make 2030 the main point of negotiation. At this date, contrary to 2020, emissions reductions may be significant, and if the level of effort is high enough, then the field of possibilities will be opened up for 2050.