Temporary Overshoot of Global Temperature Targets: A New Reality in Climate Science

The concept of temporarily exceeding global temperature targets—particularly the critical 1.5°C threshold established by the Paris Agreement—has transitioned from a theoretical modeling scenario to a tangible feature of contemporary climate pathways. A groundbreaking study published in Nature Climate Change, led by the Euro-Mediterranean Center for Climate Change (CMCC) in collaboration with 14 research institutions across 10 countries, traces this evolution over the past three decades.

What began as an exploratory tool for understanding ambitious climate goals has become, according to the research, an almost inevitable outcome in scenarios compatible with the Paris Agreement. The study reveals how the tension between increasingly ambitious temperature targets and the persistent growth of greenhouse gas emissions has transformed overshoot from a modeling curiosity into a structural characteristic of our climate future.

From Modeling Tool to Structural Reality

The research team examined how the concept of temperature overshoot has evolved since the early 1990s. Initially, overshoot scenarios were developed as thought experiments to understand what might happen if global temperatures temporarily exceeded specific thresholds before returning to safer levels through aggressive mitigation efforts.

However, as the Paris Agreement established more ambitious targets—particularly the 1.5°C goal alongside the “well below 2°C” objective—the modeling community found that scenarios consistent with these targets increasingly featured temporary overshoot periods. This shift reflects a sobering reality: the gap between where emissions are heading and where they need to be has grown so large that temporary exceedance of temperature thresholds has become the most plausible pathway to meeting long-term climate goals.

The Mathematics of Inevitability

The study’s analysis reveals that the probability of overshoot has increased dramatically since the Paris Agreement was signed in 2015. Under scenarios that give at least a 50% chance of limiting warming to 1.5°C by 2100, temporary exceedance of this threshold during the 21st century is now the norm rather than the exception.

This mathematical reality emerges from the fundamental challenge of balancing the carbon budget. With current emissions trajectories, the remaining carbon budget consistent with 1.5°C is so small that most plausible scenarios require a period of “borrowing” against future carbon removal capacity. This manifests as temporary temperature overshoot, followed by a return to safer levels through a combination of emissions reductions and carbon dioxide removal technologies.

The Tension Between Ambition and Reality

The research highlights a fundamental tension in climate policy: as our scientific understanding of climate risks has improved, and as political commitments have become more ambitious, the gap between these goals and achievable emissions pathways has widened. This creates what the authors describe as a “credibility gap” between stated ambitions and plausible implementation pathways.

The study finds that this tension has intensified over time. In the 1990s, when climate targets were less ambitious, overshoot scenarios were relatively rare in the literature. By the 2010s, following the Copenhagen Accord and the Paris Agreement, overshoot had become the dominant paradigm in climate modeling. Today, scenarios that avoid overshoot entirely require either unprecedented near-term emissions reductions or assumptions about future carbon removal technologies that may be unrealistic.

Implications for Climate Policy and Public Perception

The normalization of overshoot scenarios carries significant implications for climate policy and public communication. On one hand, overshoot scenarios demonstrate that ambitious targets remain achievable, albeit through pathways that temporarily exceed dangerous thresholds. This could be seen as maintaining hope for meeting Paris Agreement goals.

On the other hand, the study raises concerns about the psychological and political impacts of overshoot becoming normalized. If temporary exceedance of critical thresholds becomes accepted as inevitable, it could reduce the urgency of near-term emissions reductions. Additionally, the study notes that overshoot scenarios often rely heavily on future carbon dioxide removal technologies that remain unproven at scale, potentially creating a moral hazard where current inaction is justified by speculative future solutions.

The Role of Carbon Dioxide Removal

A central finding of the research concerns the role of carbon dioxide removal (CDR) technologies in overshoot scenarios. The study finds that virtually all overshoot pathways compatible with the Paris Agreement assume substantial deployment of CDR technologies, including afforestation, bioenergy with carbon capture and storage (BECCS), and direct air capture.

However, the scale of CDR deployment required in many overshoot scenarios—often hundreds of billions of tons of CO2 removal over the 21st century—exceeds current technological capabilities and raises questions about feasibility, sustainability, and social acceptance. The study emphasizes that while CDR may be necessary, it cannot substitute for immediate emissions reductions.

Regional and Temporal Variations

The research also examines how overshoot manifests differently across regions and time periods. Some regions, particularly the Arctic and small island developing states, may experience more severe and prolonged overshoot impacts due to regional amplification of global warming trends. The study finds that these regional variations could have profound implications for adaptation planning and climate justice considerations.

Temporally, the research suggests that the duration and severity of overshoot periods will significantly influence climate impacts. Shorter overshoot periods with smaller temperature excursions may have manageable impacts, while longer or more severe overshoot could trigger irreversible changes in ice sheets, ecosystems, and ocean circulation patterns.

Looking Forward: Research Priorities and Policy Needs

The study identifies several critical research priorities emerging from the normalization of overshoot scenarios. These include improved understanding of the relationship between temporary temperature exceedance and irreversible climate impacts, better quantification of the risks associated with large-scale carbon dioxide removal, and enhanced modeling of the socio-economic factors that influence the feasibility of overshoot pathways.

From a policy perspective, the research suggests that climate strategies need to account for the likelihood of overshoot while simultaneously working to minimize its duration and severity. This requires a dual approach: maintaining ambition for long-term temperature goals while recognizing that temporary exceedance may be unavoidable, and ensuring that overshoot scenarios remain as short and shallow as possible through accelerated emissions reductions.

The Path Ahead

As the world approaches the critical decade for climate action, the findings of this comprehensive study underscore the urgency of addressing the fundamental disconnect between climate ambitions and current emissions trajectories. While overshoot scenarios demonstrate that ambitious targets remain theoretically achievable, they also highlight the narrowing window for action and the increasing reliance on uncertain future technologies.

The research ultimately presents a nuanced picture: temporary overshoot of critical temperature thresholds is no longer a distant possibility but a likely feature of our climate future. However, the depth, duration, and ultimate consequences of this overshoot remain within human control through the choices made in the coming years. The challenge for policymakers, scientists, and society at large is to navigate this reality while maintaining the urgency and ambition necessary to minimize both the likelihood and impacts of temporary temperature exceedance.

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