A 2025 study finds that a year above 1.5°C likely signals a permanent breach of the Paris Agreement threshold, urging urgent climate action.
The Paris Agreement aims to limit global warming to well below 2°C, ideally 1.5°C above pre-industrial levels, measured as a 20-year average temperature threshold. However, in 2024, Earth exceeded 1.5°C for an entire calendar year for the first time. This study investigates whether this single-year exceedance signals that we are already within the 20-year period where the 1.5°C target will be permanently breached.
Using observational datasets and CMIP6 climate model simulations, the researchers assess the relationship between short-term warming events and the long-term Paris Agreement threshold, providing critical insights for climate policy and risk management.
Key Findings: What Does a Year Above 1.5°C Mean?
2024: The First Year Above 1.5°C
Global mean surface air temperature in 2024 was 1.55°C above pre-industrial levels, surpassing the Paris threshold for the first time.
This follows the 1.43°C warming recorded in 2023, which was partially driven by El Niño and anthropogenic climate change.
Paris Agreement Threshold: 20-Year Average vs. Single Years
The Paris Agreement defines 1.5°C as a long-term 20-year warming level, rather than individual years above the threshold.
However, historical data shows that once a single year surpasses a warming threshold (e.g., 0.6°C, 0.7°C, 1.0°C), it typically falls within the first 20-year period exceeding that level.
Statistical Likelihood of Entering the 1.5°C Era
99% probability: If emissions continue at current rates (SSP2-4.5 scenario), 2024 is part of the first 20-year period exceeding 1.5°C.
75% probability: Even under the most ambitious low-emission scenario (SSP1-1.9), the world is still likely to cross the 1.5°C boundary permanently in the coming years.
These results suggest that the world has likely entered the 20-year period during which the Paris Agreement’s 1.5°C goal is exceeded.
Drivers of the 2024 Temperature Surge
Anthropogenic Warming
Human-driven emissions have already caused 1.31°C (1.1–1.7°C) of warming.
Decades of rising greenhouse gases are the primary force behind recent record-breaking temperatures.
El Niño and Natural Variability
The 2023–2024 El Niño contributed an estimated 0.07°C to global temperatures.
However, natural variability alone cannot explain the record heat of 2024—underlying climate change is amplifying extreme events.
Additional Forcing Factors
Reduced aerosols from shipping regulations (2020) have decreased global cloud cover, allowing more sunlight to reach Earth’s surface.
The 2022 Hunga Tonga eruption injected large amounts of water vapor into the stratosphere, further amplifying warming.
These external influences may have accelerated the breach of 1.5°C, but they do not alter the long-term warming trajectory caused by greenhouse gases.
What Happens Next? Long-Term Risks and Climate Policy
Impacts of Entering the 1.5°C Warming Period
If the world has indeed entered a sustained period above 1.5°C, it means that:
Increased climate extremes: More frequent heatwaves, wildfires, and floods.
Accelerating ice melt: Increased risks of irreversible ice sheet loss and sea level rise.
Stronger climate feedbacks: Permafrost thawing and forest diebacks could amplify warming beyond human control.
Mitigation Strategies: Can We Stay Below 1.5°C?
Stringent emission reductions could still delay or limit the time spent above 1.5°C.
Reducing warming rates from the current 0.026°C/year to 0.005°C/year would halve the probability of a long-term breach.
Rapid deployment of carbon dioxide removal (CDR) technologies is essential to bring temperatures back below 1.5°C if exceeded.
Conclusion: A Call for Immediate Climate Action
This study provides strong evidence that a single year above 1.5°C is a warning sign of permanent exceedance. The likelihood that Earth has already entered the 1.5°C era is overwhelmingly high, unless urgent global climate action is taken.
A year above 1.5°C is not the time for despair—it is a call to action. Governments must act immediately to reduce emissions, implement adaptation measures, and prepare for the escalating risks of a hotter world.
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