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?

Summary

  • The Climate Action Tracker (CAT), the UNFCCC Synthesis Report and the UNEP 2015 Emissions Gap Report (EGR) (to which the CAT had an input) estimate global emission levels by 2025 and 2030 from Intended Nationally Determined Contributions (INDCs) submitted as of 1 October 2015, and compare these to levels required to hold warming below 2°C in the long term, and, in the case of UNEP and CAT, to below 1.5°C by 2100. The UNFCCC report does not assess the gap to achieve a 1.5°C warming limit.
  • The three analyses essentially come to very similar and comparable results for 2025 and 2030 global emissions projections based on INDCs submitted as of 1 October 2015, the emissions gap between these levels and what is needed for emissions pathways likely to hold warming below 2°C. While the UNEP report assessed the ‘likely’ probability level of 2°C by 2100, both UNFCCC and CAT assessed scenarios that exceed this probability level over the whole of the 21st century (UNFCCC: “over all times”).
  • Within uncertainties the CAT and UNEP 2015 EGR estimate similar levels of warming using very different methodologies. The UNEP 2015 Emissions Gap Report estimates the INDCs would put the world on track to a temperature rise of around 3°C by 2100. As previously reported the CAT estimated that the INDCs submitted as of 1 October 2015 (if fully implemented) will result in 21st century likely below 3°C with a central estimate of 2.7°C and a 90% chance of warming above 2°C.
  • Both CAT and the UNEP 2015 EGR estimate the gap between INDCs and emission levels for 1.5°C, finding the gaps in 2025 and 2030 somewhat larger than for 2°C. The principal divergence between 1.5°C and 2°C emission pathways emerges in the 2030-2050 period, during which time the scaling up of deep-reduction technologies and options must take place at a much larger scale and more rapidly to achieve 1.5°C.
  • For 2025, all three studies agree that the gap between INDCs submitted as 1 October 2015 and the likely below 2°C emission paths is substantial. The UNFCCC synthesis report shows that the INDC levels for 2025 are significantly above the least-cost emission pathways for likely below 2°C. The most optimistic estimates of INDC emission levels in 2025 are not far above maximum levels that might still lead to below 2°C, or below 1.5°C by 2100, pathways.
    • All three reports indicate that an increase in ambition for 2025 would be needed to close emissions gap safely for likely below 2°C pathways and to keep open the option of limiting warming below 1.5°C by 2100.
    • The CAT concludes that 2025 INDC levels are just above the current “edge of feasibility” estimates for limiting warming below 2°C, or below 1.5°C by 2100.
    • The CAT tries to address the question of whether it is possible to catch up if global emissions by 2025 are not further reduced from the presently estimated INDC levels, finding that this may be possible, but will require significantly faster rates of emission reduction and significantly higher cost than would otherwise be necessary.
  • By 2030, all studies agree the gap grows very rapidly, and becomes very large, prompting all three studies to bring into question the feasibility of holding warming below 2°C with a likelyprobability from the presently estimated 2030 INDC levels. The UNFCCC observes that “much greater emission reductions effort than those associated with the INDCs will be required in the period after 2025 and 2030 to hold the temperature rise below 2 °C above pre-industrial levels“.
    • The CAT concluded that there is major risk that if current INDCs are locked in for 2030 and not reviewed and strengthened every five years, starting in 2020, achievement of the likely below 2°C limit is fundamentally threatened, and the 1.5°C limit may be locked out
    • The UNFCCC conclusion that “...the possibility of keeping the temperature increase below 2°C still remains” from current INDC 2030 emission levels applies only to limiting warming below 2°C with a probability of around 50%.
  • The CAT finds that the UNEP EGR and UNFCCC Synthesis Report results lead to a conclusion that to hold warming below 2°C with a likely or greater probability, and to keep open limiting to below 1.5°C by 2100, INDCs for 2030 must be substantially stronger than those currently on the table.
  • The UNFCCC Synthesis Report and CAT recognise the importance of five-year cycles for improving INDCs, and all three studies emphasise the INDCs’ need to be seen as a platform for increasing ambition, including for 2025 and 2030.

Introduction

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.

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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.

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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

  • The UNFCCC report does not assess the gap to achieve the 1.5°C goal.
  • IPCC AR5 assessed 1.5°C scenarios in its reports and SPMs.
  • The UNEP Gap Report 2014 and 2015 includes those 1.5°C scenarios assessed in the IPCC AR5.
  • The UNEP Gap Report 2015 estimates the emissions levels by 2025 and 2030 required to hold warming below 1.5°C by 2100 and provides qualitative statements on additional requirements for 1.5°C in its published summary.
  • CAT estimates the gap between INDC levels and levels for 1.5°C, noting that:
    • The gaps in 2025 and 2030 are somewhat larger than for 2°C
    • The principal divergence between 1.5°C and 2°C emissions emerges in the 2030-2050 period, during which scaling up of deep-reduction technologies and options must take place at a larger scale and more rapidly to achieve 1.5°C.
    • In the emissions scenarios from the scientific literature, negative CO2 emissions for 1.5°C are no more extreme than what is ultimately needed for 2°C, but need to be achieved 5-10 years earlier

2. Rapid increase of gap in 2025-2030 period

  • All studies compare “central estimate” numbers (medians) of a wide range of 2°C pathways to INDC levels.
  • All studies agree that while the gap between INDC and 1.5/2°C levels is substantial in 2025, the gap grows very rapidly and becomes much larger by 2030
  • The very large gap by 2030 prompts all studies to bring into question any feasibility of holding warming below 1.5 and 2°C from 2030 INDC levels
  • In addition, the CAT evaluates explicitly what the maximum “allowed” levels are in 2025 and 2030 that is found in energy-economic pathways. In a sense this can be interpreted as the current understanding of the “edge of feasibility.”
  • An important conclusion is that while 2025 INDC levels are just outside of current “edge of feasibility” estimates for 1.5 and 2°C pathways, 2030 INDC levels are substantially above the highest feasibility estimates.
  • Critically global emissions are still rising by 2030, whereas these must be firmly on a downward trajectory by that time in feasible 1.5 and 2°C pathways.

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

  • All studies note that achieving 2°C from 2030 INDC levels will be extremely hard, if not impossible.
  • None of the energy-economic modelling scenarios assessed by the UNEP Gap Report allow the world to shift onto a likely below 2°C compatible pathway, based on current country 2030 commitments.
  • The UNFCCC Synthesis, unfortunately, is inconsistent in its assessment of 2030 emission levels:
    • Like the other studies the 2025 and 2030 emissions gaps are assessed with a focus on a ‘likely’ chance to hold warming below 2°C.
    • However for post-2030 feasibility from 2030 INDC levels, the UNFCCC uses emissions pathways that do not keep warming below 2°C with a likely (greater than 66% probability) but instead have about a coin-toss (50%) chance to hold warming below 2°C in the 2nd half of the 21st century..
    • Only a handful of scenarios in the AR5 still achieve 2°C with a likely chance based on current INDC emission levels in 2030. However, these rely on extreme high emissions of sulphur [2], at a level that can best be characterized as geo-engineering, and are still coupled with relatively high carbon emissions. This is arguably unrealistic and, even if they came to pass, would result in other severe environmental impacts such as high levels of ocean acidification.
    • As a consequence the UNFCCC Synthesis conclusion that “the possibility of keeping the temperature increase below 2°C still remains” applies only to about a coin-toss (50%) chance of holding warming below 2°C.
[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.

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