For years, the global climate debate has revolved around global warming—1.5 degrees Celsius or 2 degrees Celsius—and the year 2100. Beyond these warming limits, science warns that climate impacts may surpass the ability of natural and human systems to adapt. The implicit assumption was that 1.5 degrees Celsius or 2 degrees Celsius represented distant thresholds—serious, but manageable. New evidence shows that a 1.5 degree Celsius guardrail is no longer a distant target for 2100. It is unfolding within this decade. The framing of a distant goal now requires urgent recalibration.

Earth’s temperature has increased by about 0.35 degrees Celsius between 2015 and 2025, compared with 0.2 degrees Celsius per decade from 1970 to 2015. It is the fastest decadal warming rate since modern records began in 1880. 2024 was the hottest year on record at 1.55 degrees Celsius, above pre-industrial levels.

The planet is on track to reach critical global warming thresholds sooner than anticipated. Forecasts from the European Centre for Medium Range Weather Forecasts suggest that a moderate-to-strong El Niño in late 2026 could push global temperatures higher, potentially making 2027 one of the hottest years ever. The baseline warming from greenhouse gases continues to rise, and El Niño events operate on top of an already warmer climate, temporarily pushing global temperatures above 1.5 degrees Celsius. Two or three record hot years breaching this threshold in quick succession are more than symbolic. If a sustained global temperature rise of 1.5  degrees Celsius continues for a decade, global warming will no longer be episodic but persistent with potentially irreversible consequences.

The possibility of overshoot, in which global temperature temporarily exceeds a target before returning to it, is treated as manageable in climate-economic models. The assumption is that aggressive mitigation and rapid future carbon removal will restore temperatures to safer levels. But this rests on fragile foundations. The carbon budget left to keep warming below 1.5 degrees Celsius without overshoot is nearly exhausted. Large-scale deployment of negative emissions technologies (carbon dioxide removal, capture, utilisation, storage) remains uncertain. The effectiveness, risks and governance of climate geoengineering, including solar radiation modification, remain deeply uncertain and potentially perilous.

Most importantly, the Earth system may not respond linearly to temporary warming excursions and climate geoengineering interventions. Overshoot may trigger processes that are effectively irreversible on human timescales.

Instability in the South Asian monsoon could affect billions of people and food systems. Accelerated Himalayan glacier loss could threaten freshwater supplies across major Asian river basins. Even transient exceedance of 1.5 degrees Celsius may increase the probability of triggering such changes, yet robust quantification of ‘how much overshoot is too much, and for how long’ remains lacking.

The emerging ‘new state of climate’ is defined not only by temperature overshoot but also by potential intensification of cascading and compounding risks. We are already witnessing concurrent heatwaves, droughts and wildfires; floods and landslides; marine heatwaves devastating coral reefs; and glacier retreat increasing downstream flood hazards. Under overshoot scenarios, interacting hazards are likely to become more frequent, more intense and more complex.

Climate linkages between distant regions (teleconnections) may amplify impacts in unpredictable ways: Arctic warming influences mid-latitude extremes; changes in ocean circulation may alter monsoon dynamics; and forest dieback could accelerate atmospheric carbon accumulation. The result is a shift towards a more complex and dangerous risk regime in which multiple hazards overlap in time and space, straining both natural and socioeconomic resilience.

Despite decades of scientific progress, we still lack credible assessments of the likelihood and timing of abrupt tipping events under transient and sustained global or regional temperature overshoot. Earth system response to global net-zero emissions is not fully understood, particularly if overshoot occurs. It is uncertain whether the global temperature will decline symmetrically after peak warming or whether feedback will prolong elevated temperatures. Regional consequences, critical thresholds, teleconnections, cascading and compounding effects and adaptation limits under high-end warming scenarios are insufficiently quantified. Overshoot pathways are often presented as reversible, but the natural world may not be so accommodating.

Climate change is outrunning our mitigation efforts. While net zero pledges have expanded globally, current emission trajectories remain inconsistent with limiting warming to 1.5 degrees Celsius without significant overshoot. Still, fossil fuel dependence persists, and renewable energy deployment is accelerating. It has yet to displace emissions at the required scale.

Each year of delayed or insufficient mitigation increases the probability of deeper, longer overshoots, narrowing the margin for error. Adaptation has limits. Urban heat adaptation can reduce mortality, but extreme heat beyond physiological thresholds threatens public health and productivity. Agricultural systems can diversify and innovate, but multi-year droughts combined with extreme heat or extreme rainfalls may exceed resilience capacity. Overshoot heightens the risk that adaptation measures will be overwhelmed or rendered economically unviable, particularly in vulnerable regions.

Policymakers and researchers must focus on minimising both the magnitude and the duration of any temperature overshoot. This requires rapid, deep and sustained emission reductions, accelerated renewable energy transitions, and the protection and restoration of natural carbon sinks. Scientific research must intensify its focus on overshoot, tipping elements, early warning indicators and cascading risks. Enhanced observation systems for oceans, glaciers, forests and the atmosphere are essential. Modelling efforts must better integrate threshold behaviour, compound extremes and overshoot pathways.

Climate risk assessments should shift from equilibrium thinking to threshold-aware frameworks that explicitly account for abrupt and nonlinear change. Governance structures must also evolve accordingly. Climate risk stress testing should become standard for infrastructure planning and financial systems. Regional cooperation is needed, particularly in monsoon-dependent and glacier-fed regions where transboundary water and food security risks are escalating. Disaster risk reduction must be fully aligned with forward-looking, robust climate projections, including overshoot rather than historical baselines that no longer represent future reality.

Climate is entering a new state, characterised by systemic risk and narrowing margins for stability. The narrative that 1.5 degrees Celsius is a distant concern has collapsed. Temporary exceedance is becoming a lived experience of this decade. Whether it remains temporary or locks the planet into a more dangerous trajectory depends on decisions taken now. Overshoot is an imminent policy challenge. The window to limit its depth, duration and irreversible consequences is closing rapidly.