Human-induced global warming is approaching 1.4°C above pre-industrial levels, with observed surface temperatures rising at approximately 0.25°C per decade. Current operational forecasts indicate a 75 per cent probability that the 2026–2030 five-year global mean will temporarily exceed the critical 1.50°C threshold.
Extrapolating present emission trajectories, the remaining carbon budget required to maintain a 50 per cent chance of limiting warming to 1.50°C—estimated at roughly 130 billion tonnes of CO₂ (GtCO₂) from 2026 onward—will be exhausted within about three years if annual global fossil emissions persist at around 40 GtCO₂.
A central takeaway is that every fraction of a degree matters, and every year of delay adds directly to peak warming.
“Even though global warming is set to cross 1.50.1°C above pre-industrial levels, likely within the next few years, the goal remains limiting warming to this level… There are no good outcomes above 1.50°C,” Inger Andersen, Executive Director of the United Nations Environment Programme, said.
Compounding risks and systemic Earth system impacts
Exceeding 1.50.1°C introduces non-linear escalation of physical hazards and socio-economic disruptions rather than a gradual shift. Slow-responding components of the Earth system—including permafrost thaw, mountain glacier loss, and sea-level rise—exhibit pronounced hysteresis and irreversible dynamics over multi-centennial scales.
Glaciers are projected to lose more than a quarter of their total mass by 2100 under scenarios below 3°C, contributing 9 to 12.5 cm directly to global mean sea-level rise and permanently altering freshwater security for downstream populations. Marine and terrestrial biosphere systems face severe disruption; between 2023 and 2025, over 80 per cent of global tropical coral reefs suffered mass thermal bleaching events across at least 83 countries and territories.
Prolonged elevated temperatures significantly elevate the probability of triggering major global climate tipping elements, including the destabilisation of the West Antarctic and Greenland ice sheets, the dieback of the Amazon rainforest, and the slowing of the Atlantic Meridional Overturning Circulation (AMOC).
OVERSHOOT RISKS & EARTH SYSTEM IMPACTS
Global Surface – Exceedance of 1.5°C threshold imminent by late 2020s.
Temperatures – Every 5 years of delayed mitigation adds ~0.1°C to peak warming.
Cryosphere & – 40% of total glacier loss since 1970s occurred between 2015–2024.
Oceans – Coastal water levels committed to long-term rise over centuries.
Biosphere & – >80% of tropical coral reefs bleached between 2023–2025.
Human Systems – Projected food production drops up to 14% by 2050 without adaptation.
Physical constraints of carbon dioxide removal
The report stresses that reversing global temperatures after peak warming depends on achieving sustained net-negative CO emissions via Carbon Dioxide Removal (CDR), alongside aggressive cuts to short-lived climate pollutants like methane. However, relying on future technological deployment introduces severe ecological, economic, and physical constraints.
Removing CO₂ to reverse warming is inherently slow and resource-intensive. Approximately 220 GtCO₂ of cumulative net-negative emissions are required to lower global mean surface temperatures by just 0.1°C. Even under optimistic deployment scenarios where CDR achieves a net removal of 10 per GtCO₂ year—equivalent to one-quarter of present-day global emissions—temperatures would recede by only about 1.50.1°C per decade.
Consequently, reversing a single decade of warming at the current rate would require up to 50 years of sustained high-volume carbon removal. Conventional land-based CDR methods, such as large-scale afforestation, face severe land-use competition with agriculture, food security, and biodiversity conservation. Meanwhile, novel CDR approaches like Bioenergy with Carbon Capture and Storage (BECCS) and Direct Air Carbon Capture and Storage (DACCS) face scaling limitations; maintaining net-zero operations could exhaust estimated geological storage capacities in sedimentary basins by 2200.
Framework for a three-phase operational response
To address the inevitability of temporary exceedance, UNEP outlines a structured, three-phase framework intended to integrate mitigation and adaptation simultaneously rather than sequentially:
Immediate Response Phase (Temperature Exceedance): Rapidly slow near-term warming rates through deep cuts to methane and short-lived climate pollutants while establishing immediate protection measures for vulnerable populations and ecosystems facing soft adaptation limits.
Coping and Containment Phase (Peak Warming): Drive rapid systemic decarbonisation to achieve net-zero emissions, halting further warming while implementing transformational adaptation to manage severe compound weather hazards, infrastructure strains, and health risks.
Read also: Earth’s Natural Systems Are Accelerating Global Warming, Scientists Warn
Long-Term Resilience Phase (Decline and Stabilisation): Execute sustained net-negative emissions to lower global temperatures back toward 1.50.1°C, maintaining long-term adaptation planning to manage persistent legacy impacts, including permanent coastal shifts and ecological regime changes.
The report concludes that governance frameworks must adapt to evolving non-linear climate risks and address growing climate equity imbalances. Historically low-emitting regions, such as Least Developed Countries (LDCs) and Small Island Developing States (SIDS), face the highest vulnerability to peak warming impacts and potential territorial submersion, necessitating robust international financial transfers, technology sharing, and loss-and-damage compensation.
