Navigating the Overshoot: Insights on exceeding global warming thresholds

The ambition to limit global warming to 1.5°C, as established under the Paris Agreement, has long served as a cornerstone of international climate policy. Yet, as greenhouse gas (GHG) emissions continue to rise and climate impacts intensify, the probability of temporarily exceeding this threshold, commonly referred to as temperature overshoot, is becoming increasingly likely.

According to the Intergovernmental Panel on Climate Change (IPCC), even under low emissions scenarios, there is at least a 50% likelihood that global temperatures will breach 1.5°C in the near future. This shifting climate reality underscores the urgent need to assess the risks, societal implications, and pathways to potentially return to safer temperature levels. In response, the CMCC Foundation has led the development of an innovative Overshoot Platform, supported by an international network of scientists and policy experts, offering critical insights into this complex challenge.

The concept of “overshoot” describes scenarios in which global temperatures temporarily exceed the 1.5°C threshold before declining again due to mitigation efforts such as carbon dioxide removal (CDR). Three principal warming pathways are considered: stabilisation below 1.5°C, overshoot followed by decline, and permanent stabilisation above 1.5°C.

Each pathway poses different risks to ecosystems, economies, and societies. In overshoot scenarios, even short-term increases in warming could push vulnerable systems beyond tipping points, leading to irreversible damage. Coral reefs, polar ice sheets, and tropical rainforests are particularly at risk of collapse, with cascading global effects.

CMCC’s recent review paper, Overshoot: A Conceptual Review of Exceeding and Returning to Global Warming of 1.5°C, provides a comprehensive analysis of overshoot dynamics. The research assesses climate risks, global emissions pathways, adaptation challenges, and the policy decisions that will define our ability to respond to this future.

A key finding in the CMCC’s research is the asymmetry between warming and cooling in the Earth system. While global surface temperatures may decline following net-negative emissions, other components, such as sea-level rise and permafrost thaw, may not recover on comparable timescales. Some processes are irreversible over centuries, highlighting the lasting consequences of even temporary overshoot.

Projects like RESCUE delve into these delayed Earth system responses, quantifying the increased probability of tipping points and irreversible change under delayed mitigation trajectories. Similarly, CMCC’s C-BLUES and CONCERTO projects investigate how carbon ecosystems, such as forests and soils, can buffer climate hazards. CONCERTO, in particular, focuses on developing an integrated framework to monitor and model terrestrial carbon cycle dynamics, a vital step for improving Earth system model projections.

The CMCC’s Overshoot Platform illustrates how climate risks evolve across three warming scenarios, revealing the compounding role of hazard, exposure, vulnerability, and response capacity. In an overshoot world, heightened weather extremes exacerbate systemic risks.

These findings reaffirm the need for multidisciplinary approaches that align climate science, socio-economic pathways, and ecosystem modelling. CMCC’s NEWPATHWAYS project exemplifies this approach by co-designing decarbonisation strategies with stakeholders, aiming to balance mitigation urgency with adaptation capacity and equity considerations.

Reversing warming trends requires achieving net-zero emissions rapidly, targeting short-lived climate pollutants such as methane, and deploying scalable CDR technologies. CMCC’s UPTAKE project examines the feasibility of such technological deployment, alongside the governance structures needed for equitable fossil fuel phase-out. Meanwhile, OceanICU explores the role of marine ecosystems in carbon absorption and their interactions with human pressures.

Despite these efforts, the path forward is fraught with challenges - technical, social, and economic. Overshoot pathways are not purely scientific questions; they are shaped by political will, public engagement, and international cooperation.

The window to avoid irreversible impacts is narrowing. Navigating an overshoot future demands accelerated mitigation, equitable adaptation strategies, and cross-disciplinary collaboration. CMCC’s work, through both scientific research and digital platforms, equips decision-makers with the tools to understand, communicate, and act upon this pressing global challenge.

CONCERTO contributes to this mission by enhancing our understanding of land carbon dynamics and improving the integration of carbon cycle feedbacks in climate models. In an overshoot world, such insights are vital to ensuring a sustainable, just, and resilient future.