1.5°C Warming Breach Now Seen as Unavoidable: the Overshoot, Peak, and Decline Pathway
Global average temperature crossed the 1.5°C threshold above pre-industrial levels for a full calendar year in 2024, a benchmark set by the Paris Agreement
The United Nations Environment Programme has assessed that a further, sustained breach of the 1.5°C limit in the coming years is now effectively unavoidable under current emission trajectories
Analysis frames the response not as preventing the breach but as managing an "overshoot, peak, and decline" pathway — temporarily exceeding 1.5°C, minimising and shortening the peak, and later pulling temperatures back down through deep decarbonisation and carbon removal
Under presently implemented policies, global warming is projected to reach around 2.6°C by 2100, well above the Paris Agreement's goals
Paris Agreement Temperature Goal and the 1.5°C Threshold
Article 2 of the Paris Agreement (adopted at COP21, 2015) commits parties to hold the increase in global average temperature to "well below 2°C above pre-industrial levels" while "pursuing efforts" to limit the increase to 1.5°C, recognising this would significantly reduce climate risks. The 1.5°C figure is measured as a long-term, multi-decade average rather than any single year's temperature.
The single-year breach in 2024 is an early signal, not final confirmation, that the Paris Agreement's aspirational 1.5°C goal is being missed on the sustained-average basis the treaty actually measures.
IPCC Carbon Budget and Overshoot Pathways
The IPCC's Sixth Assessment Report (AR6, 2021-2023) quantifies the "remaining carbon budget" — the amount of additional CO2 that can be emitted globally while retaining a given probability of staying within a temperature limit. Pathways that temporarily exceed 1.5°C before returning below it through negative-emissions technologies are termed "overshoot" scenarios.
The "overshoot, peak, and decline" framing described in the article mirrors precisely the IPCC's own overshoot-pathway language — accepting a temporary breach while emphasising the need to minimise its magnitude and duration through the same carbon-budget mathematics AR6 uses.
UNEP Emissions Gap Reports and the Policy-Ambition Shortfall
UNEP's annual Emissions Gap Report tracks the difference between countries' current climate pledges (NDCs), the emission cuts actually delivered by existing policies, and the reductions needed to meet the Paris Agreement's goals. It is the standard reference for how far off-track the world remains from 1.5°C and 2°C pathways.
Key Details
- UNEP reports have consistently found that emissions under current policies put the world on track for warming well above 2°C by 2100 (recent estimates cluster around 2.6-2.8°C)
- The "emissions gap" is defined as the difference between projected 2030 emissions under current pledges and the level required for 1.5°C/2°C-consistent pathways
- UNEP's reports distinguish "unconditional" NDCs (pledged without external support) from "conditional" NDCs (contingent on finance/technology transfer), with conditional pledges narrowing the gap further if fully implemented
The article's cited 2.6°C-by-2100 projection under current policies is consistent with UNEP Emissions Gap Report findings, reinforcing that the policy-ambition shortfall — not just physical climate inertia — is what makes an overshoot of 1.5°C effectively locked in.
- 2024: first calendar year with global average temperature exceeding 1.5°C above pre-industrial levels
- Paris Agreement (COP21, 2015): Article 2 sets the "well below 2°C, pursue 1.5°C" goal, entered into force November 2016
- IPCC AR6 remaining carbon budget (Jan 2020): 340-400 GtCO2 for 67% chance of 1.5°C; ~250 GtCO2 for 50% chance as of 2023
- No/limited-overshoot pathways require ~45% cut in global net CO2 emissions from 2010 levels by 2030; net-zero CO2 around 2050
- Current-policy warming projection by 2100: approximately 2.6°C
- India's NDC (2022): 45% emissions-intensity reduction by 2030 (vs 2005); 50% non-fossil power capacity by 2030