Explainer: What the new CMIP7 emissions scenarios say about future warming

# What CMIP7 changes and why it matters Every six to seven years, climate modelling groups run coordinated simulations to test how the climate might respond to different human choices. CMIP7 provides the next standard set of future emissions pathways that global models will use for the IPCC's seventh assessment cycle.

New naming and framing of scenarios

A narrower range of warming outcomes

The seven new scenarios give 2100 warming between 1.6°C and 3.3°C above pre-industrial levels. By contrast, the SSPs used in AR6 implied a 2100 range of roughly 1.5°C to 4.7°C. This is the first time in four modelling generations that the top of the scenario range has fallen noticeably.

The medium scenario — intended to represent current policies — reaches about 2.9°C by 2100, crosses 2°C around mid-century, and approaches 3°C by about 2110. There is a one-in-four chance that this medium pathway exceeds 4°C by 2150.

Why the top end moved down

High-end future emissions were revised down substantially because a 21st century dominated by coal is now judged implausible. The new high scenario produces about half the cumulative CO2 of the highest scenarios used in the three previous IPCC cycles, which previously produced around 4.6–4.9°C by 2100.

Lower-end scenarios shifted up

The very-low scenarios are modestly higher than the lowest SSPs. CMIP7's very-low pathway peaks near 1.8°C mid-century and declines to around 1.5°C by 2100. The authors note that fully avoiding any overshoot of 1.5°C now looks unlikely.

Dependence on carbon dioxide removal

Socioeconomic updates

CMIP7 also updates underlying socioeconomic assumptions. For example, in the medium pathway global population peaks around 10.1 billion around 2080, and income per person in 2100 is estimated 10–25% lower than in the original SSP projections.

What to expect next

Model centres are beginning to run full Earth-system simulations using these scenarios. The emissions trajectories already clarify the narrower range of futures that will feed into the IPCC's AR7. They change the baseline framing for policy-relevant outcomes and alter the mix of mitigation and removal required to meet temperature goals.

# Bottom line CMIP7 offers a tighter, updated set of emissions pathways. They lower the highest realistic warming outcomes, raise the lowest slightly, and show that scenarios keeping warming near 1.5°C will need substantial carbon removal and different socioeconomic assumptions than earlier scenario sets.