Questionable at best: why links between mitigation by single actors and global temperature goals must be made more robust

ABSTRACT

In the academic and grey literature, near- and mid-term mitigation trajectories by single actors (countries, firms, cities or regions) are often labelled with terms including long-term temperature goals (e.g. 1.5°C scenario). Yet direct links between single actors’ mitigation efforts in the near- to mid-term and global temperature goals in the long-term are neither consistent nor defensible without making important additional assumptions about space, time and equity. We argue that such labelling should be avoided. If labelling has to be used, these assumptions should be transparently stated, to bridge spatial and temporal scales, and to make explicit ethical judgments about the distribution of mitigation efforts.

KEYWORDS:

• Global temperature goal
• labelling mitigation actions
• downscaling global emission pathways
• spatial scales
• timescales
• equity

Disclosure statement

No potential conflict of interest was reported by the author(s).

Notes

1 Following IPCC AR6 WGIII, we use near-term for up to 2030 and mid-term for up to 2050.

2 Historical emissions may be counted from 1850 or 1900, roughly approximating emissions since the industrial revolution. Taking an earlier starting point may have symbolic value. However,

62% of total cumulative CO₂ emissions from 1850 to 2019 occurred since 1970 (1500±140 GtCO₂), about 42% since 1990 (1000±90 GtCO₂), and about 17% since 2010 (410±30 GtCO₂). For comparison, the remaining warming to 1.5°C with a 67% (50%) probability is about 400(500)±220 GtCO₂. (Dakhal et al., 2022)

We do not specify a single year for ‘present’ since each scenario has a different base year.

3 For the same reason, we would refrain from labeling emission levels of single countries in 2030 as 1.5°C consistent (as in Rajamani et al., 2021), even though in this case, the basis in international environment law for using the equity principles they use is very clear and applied in quantative analysis.

4 This recommendation is less applicable for actors with very small share of total emissions (e.g., individual cities, individual firms, etc.) since 'assuming one represents 0.015% of a global TCB' would not be a very useful qualifier. Furthermore, emissions of sub-national actors are part of a country’s emissions. We recommend that sub-national actors with very small shares of TCB refrain from labeling their mitigation pathways with long-term temperature goals.