1.5°C Pathway

A 1.5°C pathway is a modelled trajectory of global greenhouse gas (GHG) emissions consistent with holding the long-term increase in global mean surface temperature to 1.5°C above pre-industrial levels. The concept became central to climate diplomacy after the Paris Agreement (2015), whose Article 2 commits parties to holding warming "well below 2°C" while "pursuing efforts" to limit it to 1.5°C.

The IPCC's Special Report on Global Warming of 1.5°C (SR1.5, 2018) translated this political target into quantitative benchmarks. To stay within 1.5°C with limited or no overshoot, the report found that global net anthropogenic CO2 emissions must fall by roughly 45% from 2010 levels by 2030 and reach net zero around 2050. Methane and other non-CO2 forcers must also be reduced sharply. The IPCC's Sixth Assessment Report (AR6, 2021–2022) reaffirmed these orders of magnitude and emphasised that remaining carbon budgets are small — on the order of a few hundred gigatonnes of CO2.

Pathways consistent with 1.5°C typically share several features:

• Rapid decarbonisation of electricity, with large-scale deployment of renewables.
• Electrification of transport, buildings, and industry.
• Reductions in energy demand and improvements in efficiency.
• Some reliance on carbon dioxide removal (CDR), including afforestation, BECCS, or direct air capture, to offset residual emissions.
• Steep cuts in methane from agriculture, waste, and fossil fuel operations.

The UNEP Emissions Gap Report has repeatedly found that current Nationally Determined Contributions (NDCs) under the Paris Agreement are insufficient to put the world on a 1.5°C pathway, creating what negotiators call the "emissions gap." At COP26 in Glasgow (2021), parties agreed to "keep 1.5 alive" as a guiding political phrase, and the Glasgow Climate Pact requested strengthened 2030 targets. Debate continues over the feasibility of limited-overshoot pathways and the ethical implications of relying heavily on future CDR.