What do the CAT, UNFCCC Synthesis Report and the UNEP 2015 Emissions Gap report say about the prospects of limiting warming to below 2°C and 1.5°C from INDC levels for 2025 and 2030?

26th November 2015




Over the year 2015, more than 150 countries have submitted their offers for future greenhouse gas (GHG) reductions (Intended Nationally Determined Contributions, INDCs). A number of modelling groups have analysed the potential impact of these offers on GHG emissions projections.

This briefing compares the Climate Action Tracker’s results and approach to the most prominent assessments, the UNFCCC INDC synthesis report (UNFCCC, 2015), and the UNEP Emissions Gap Report 2015[1].

Differences in results

CAT, UNFCCC and UNEP essentially come to very similar and comparable results for global emissions in 2025 and 2030 (Figure 1). While the three studies took different approaches with regard to the number of INDCs analysed in detail, the accounting of emissions from countries with conditional INDCs as well as countries that have not submitted their INDCs (Table 1), the overall emissions level in 2030 ranged between 53 – 55 GtCO2e for CAT, 53 – 59 GtCO2e for UNFCCC, and 52 – 59 GtCO2e for UNEP reports, respectively. The emissions gaps from the 2°C pathway were also found to be within a similar range (Table 1). Note that the UNEP report assessed the ‘likely’ probability level of 2°C by 2100, while both UNFCCC and CAT assessed scenarios that exceed this probability level over the whole of the 21st century (UNFCCC: “over all times”).

CAT estimates for 2025 and 2030 under the INDCs are at the lower end of the UNFCCC and UNEP range. One main reason is probably that CAT carries out an up-to-date analysis of the current trends, including the policies that all major emitters have already put in place. These current policy projections are usually lower than older references used by others, because many countries are implementing polices, and because the uptake of renewables is much higher than previously estimated. The final emissions level of a country under its INDC is lower only if the INDC is more ambitious than the current policy projection. This may be an influential factor, especially for some major emitters.

Table 1: Emissions levels and emissions gap to 2°C in 2025 and 2030 and the temperature increases found by CAT, UNFCCC and UNEP Reports

With regard to temperature implications, only the CAT analysis provides estimates with the central estimate of 2.7°C, likely below 3° warming and 90% chance above 2°C from the October 1 INDCs. CAT is using a sophisticated approach, which includes selecting scenarios of similar effort after 2030 and using probabilistic climate model analysis to derive the resulting temperature increase.

The UNFCCC synthesis report does not include a temperature estimate. The press release accompanying the report included a figure of 2.7°C, but without reference to a source. We assume the source was the Climate Action Tracker.

At time of writing (6 November) the UNEP Emissions Gap Report 2015 has only its Executive Summary available and the temperature implications may be found in the main report expected to be published in the coming days. The report provides the temperature level that results from scenarios of the IPCC scenario database that have the same emissions level in 2030 as the INDCs. Taking into account the overall emission levels and the emissions gaps estimated for 2030, it is likely that the temperature increase estimates of the UNEP gap report fits in a similar range, given the uncertainties.

Table 2: Main methodological differences between CAT, UNFCCC synthesis and UNEP Emissions Gap report 2015

Implications of compatibility of INDCs with holding temperature increase below 1.5/2°C

All three studies estimate global emissions levels by 2025 and 2030 from INDCs, and compare these to levels required to hold warming below 2°C in the long term. There are important similarities as well as differences between the studies that relate to three broad topics.

1. Consideration of 1.5°C

2. Rapid increase of gap in 2025-2030 period

3. Feasibility to achieve below 2°C from 2030 INDC levels

[1] This briefing has been prepared based on the UNEP press release issued on 6 November.

[2] All IPCC AR5 scenarios with global emissions of around 55 Gt CO2-e or higher in 2030 that achieve 2°C with a ‘likely’ chance are produced by a single model (MERGE_ETL), which assumes in its scenarios that SOx emissions do not decrease with decreasing CO2 emissions from coal, currently the main (co-)emission source. These high SOx emissions have a cooling effect which results in less temperature rise by 2100. This is an unrealistic assumption for large deviations in emissions from the baseline, which is the case in 2/1.5°C consistent emissions pathways that see a phase-out of coal-fired power plans in the coming decades.