Are we really on track to limit temperature rise below 2°C?

A recent Nature article by Malte Meinshausen et al.¹ received considerable attention in the media under the headline that current countries’ pledges to reduce greenhouse gas emissions may limit global temperature rise to just below 2°C.

The article confirmed earlier assessments from the International Energy Agency² and Climate Action Tracker³ that also indicated that under certain assumptions, current pledges could limit temperature rise below 2°C (but all would fail to limit temperature rise to the 1.5°C Paris Agreement target).

These, to a certain extent “optimistic”, assessments contrast with the statements from both the UN Climate Secretariat (UNFCCC⁴) and UN Environment (UNEP⁵) which at the time of the Glasgow Climate Summit of November 2021 warned that current pledges would lead us to temperatures (well) above 2.5°C.

I aim to explain where the differences in these numbers come from.

Assessments differ hugely in whether they look at countries’ 2030 targets and policies alone or also take into account post-2030 pledges and policies, including in particular net-zero pledges. In general, looking beyond 2030 gives more optimistic results. But it should be clear that looking beyond 2030 also substantially increases the level of uncertainty.
Whether the assumed temperature limit linked to the assessment of 2030 pledges and policies will actually be achieved depends on whether the pledges are actually implemented or not. And there are many reasons why this is far from certain, including the lack of integration of pledges into policies and measures, lack of financial means, the impact of Covid and/or the Russian invasion of Ukraine.

Assessing the impacts of pledges and action beyond 2030 is however even more uncertain as this depends on:

• whether pledges (both for 2030 and in the longer term) will actually be implemented;
• whether countries actually intend to sustain the pledged action after 2030; and
• whether countries are able to overachieve their 2030 targets in order to achieve their net-zero pledges.

In addition, several of the assessments on which these long-term pledges are based also include the potential impact of collective pledges, through the efforts of ICAO (on international aviation), IMO (on international shipping) or the Global Methane Pledge, for example. This adds another layer of uncertainty as there is a risk of double counting of national and collective action.

Just before the Glasgow Climate Summit of November 2021, three reports assessing 2030 climate pledges were published: the UNFCCC’s revised synthesis report of Nationally Determined Contributions under the Paris Agreement (October 2021); UNEP’s Emissions Gap Report 2021 (November 2021); and Climate Action Tracker’s Warming Projections Global Update (November 2021).

These three reports came to rather similar conclusions (temperature rise of 2.4°C to 2.7°C) and differ basically on:

• the type of pledges included in the assessment; and
• the baseline for comparison of estimated 2030 emissions.

The UNFCCC report assesses all national contributions (NDCs) that countries submitted to the UN by October 2021. The UNEP report assesses all the above pledges, as well as pledges that countries announced before COP26 but did not submit (in time) for the UNFCCC report, which includes pledges from China, Korea and Japan. The CAT report assesses all of the above as well as the impact of existing policy scenarios for those countries where projected emissions based on existing policies are lower than countries’ pledged emissions limitations. Table 1 below provides an overview of the results of these assessments.

Table 1: Comparing estimated emissions in 2030 from different assessments (in GtCO₂-e).           

The three reports also use different numbers for the level of global emissions in 2030 that would be compatible with the objective to limit temperature rise to 1.5°C, and take different approaches to the level of likelihood of achieving the 1.5°C target, as indicated in Table 2 below.

Table 2: Comparing the baselines used to estimate temperature projections

When applying UNEP’s approach to the different assessments the picture of how the different approaches lead to different results is quite clear, as shown in Figure 1.

Figure 1: Temperature projections for different assessments of countries’ NDCs, pledges and policies.

The long-term assessment made by Meinshausen et al. is based on three elements:

• 2030 pledges (as well as existing policies and measures scenarios – whichever is the lowest);
• long-term targets incl. net-zero pledges;
• extrapolation of 2030 and long-term pledges beyond 2030/2050 using Integrated Assessment Models;
• collective action on international aviation and shipping.

They conclude that full implementation of all pledges and continuation of policies and measures would limit temperature rise by the end of the century to 1.9°–2°C.

In its Announced Pledges Scenario the IEA also includes an assessment of the potential impact of the Global Methane Pledge and concludes that temperature rise could be limited to 1.8°C by the end of the century.

Climate Action Tracker uses a very similar approach and concludes in its optimistic scenario that we could be on track to a 1.8°C temperature rise.

Whichever assessment is used we are facing an implementation gap.

It is vitally important to understand that all the above assessments face the same challenge, which is the so-called implementation gap. The following four key messages from the UNEP Emissions Gap Report make it very clear that we face a number of challenges:

1. New mitigation pledges for 2030 show some progress, but their aggregate effect on global emissions is insufficient;
2. The emissions gap remains large: compared to previous unconditional NDCs, the new pledges for 2030 reduce projected 2030 emissions by only 7.5 per cent, whereas 30 per cent is needed for 2°C and 55 per cent is needed for 1.5°C;
3. As a group, G20 members are not on track to achieve either their original or new 2030 pledges. Ten G20 members are on track to achieve their previous NDCs, while seven are off track;
4. Few of the G20 members’ NDC targets put emissions on a clear path towards net-zero pledges. There is an urgent need to back these pledges up with near-term targets and actions that give confidence that net-zero emissions can ultimately be achieved and the remaining carbon budget kept.

Wendel Trio

1 Meinshausen, M. et al. (2022). Realization of Paris Agreement pledges may limit warming just below 2°C. In: Nature. 13 April 2022. www.nature.com/articles/s41586-022-04553-z. xxx
2 IEA (2021). Announced Pledges Scenario. November 2021. www.iea.org/reports/world-energy-model/announced-pledges-scenario-aps
3 CAT (2021). Glasgow’s 2030 credibility gap: net zero’s lip service to climate action. Warming Projections Global Update. November 2021. climateactiontracker.org/publications/glasgows-2030-credibility-gap-net-zeros-lip-service-to-climate-action
4 UNFCCC (2021). Nationally determined contributions under the Paris Agreement. Revised synthesis report by the secretariat. 25 October 2021. unfccc.int/documents/307628
5 UNEP (2021). The Heat Is On. A world of climate promises not yet delivered. Emissions Gap Report 2021. October 2021. www.unep.org/resources/emissions-gap-report-2021
6 Conditional pledges refer to pledges made by (developing) countries which are (in part) dependent on receiving financial and/or other support from developed countries for their implementation