Global temperatures are now widely expected to temporarily exceed the Paris Agreement’s 1.5 °C warming limit, even under the most aggressive emissions-reduction scenarios. That prospect, known as “overshoot,” is reshaping how scientists model climate risk and how policymakers assign responsibility for excess warming. Yet the operational prescription has not changed: reaching net zero carbon dioxide emissions by the early 2050s remains the single most effective tool for limiting long-term damage.
Overshoot Is Now the Expected Outcome
The IPCC’s AR6 Working Group III assessment made the situation plain: even with rapid cuts, it is almost inevitable the world will temporarily exceed 1.5 °C. Stabilization, the panel concluded, requires net zero CO2, with pathways consistent with 1.5 °C reaching that milestone by the early 2050s. The framing matters because it distinguishes between a permanent breach and a temporary one. In the temporary version, temperatures peak above the threshold and then decline as carbon dioxide removal draws down atmospheric concentrations. In the permanent version, the world simply blows past the target with no return path. Recent work in the Proceedings of the National Academy of Sciences further clarifies this distinction, defining overshoot as a temporary exceedance and examining how different emissions pathways alter the likelihood and duration of that temporary exceedance.
The IEA’s Net Zero Emissions by 2050 Scenario, or NZE, charts one of the tighter overshoot trajectories. Its modeling includes explicit treatment of peak warming and overshoot, built around rapid clean energy deployment, electrification, and efficiency gains, and is laid out in detail in the agency’s net zero scenario documentation. A companion dataset comparing the NZE pathway against IPCC AR6 1.5 °C scenario categories (C1 and C2) shows how peak temperature rise and years of overshoot differ depending on the speed of action. The gap between a five-year overshoot and a multi-decade one is not academic; it determines how many irreversible thresholds the climate system crosses along the way, and how much cumulative harm is inflicted on vulnerable communities and ecosystems before any eventual cooling.
Why the Duration of Overshoot Matters More Than the Peak
Most company and government net zero pledges fixate on the target year, typically 2050, with far less attention paid to the emissions trajectory between now and then. A Scientific Reports analysis found that most such commitments emphasize the year net zero is reached rather than the path taken to get there, including whether methane abatement is postponed, showing that delayed mitigation can significantly increase cumulative warming. That distinction carries real consequences: a slow start followed by a steep late decline produces more cumulative emissions than steady reductions from today, even if both routes arrive at the same endpoint. Because the climate system responds to the total amount of greenhouse gases emitted, not just the final emissions level, the overshoot in temperature and time is larger when cuts are backloaded.
The physical risks compound with each fraction of a degree. Research published in Nature Communications found that every 0.1 °C of additional overshoot above 1.5 °C increases the risks associated with tipping elements and concluded that greenhouse gas emissions need to reach net zero as early as possible to minimize those dangers. The OECD has similarly warned that overshooting 1.5 °C may push the earth over several tipping points, leading to irreversible and severe changes in the climate system, including destabilization of ice sheets and shifts in ocean circulation, as outlined in its work on climate mitigation. Ice sheet collapse, permafrost thaw, and disrupted circulation patterns do not reverse on human timescales, which means the length of time the world spends above 1.5 °C can lock in damage that persists for centuries even after temperatures fall back. In this light, the duration of overshoot becomes a core justice issue: longer overshoot periods expose younger generations and low-income regions to compounding, and often irreversible, harms.
The Danger of Banking on Future Carbon Removal
Overshoot scenarios all depend, to varying degrees, on carbon dioxide removal (CDR) to pull temperatures back down after they peak. The IPCC’s AR6 Synthesis Report spells out CDR’s two roles: counterbalancing residual emissions that are hard to eliminate entirely, and achieving net negative emissions to reverse overshoot. High-overshoot pathways demand significantly more CDR than limited-overshoot ones, with the IPCC quantifying the differences in cumulative net negative emissions required by 2100 across scenario categories. These modeled quantities reach into the hundreds of billions of tonnes of CO2, far beyond the capacity of current technologies such as bioenergy with carbon capture and storage or direct air capture, which today operate only at pilot or early commercial scales.
A peer-reviewed Commentary in Nature raises a pointed objection to the comfort many draw from such models. The authors argue that overshoot framing can encourage delay or excessive confidence in future carbon removal, examining how pathway ensembles treat the relationship between residual emissions reductions, non-CO2 mitigation, and total CDR needs, and they warn that this reliance risks turning CDR into a form of dangerous procrastination. A related access portal underscores how the same analysis questions whether policymakers are underestimating the political and technical barriers to scaling CDR, with the underlying study emphasizing that no removal technology currently operates anywhere near the levels assumed in many overshoot pathways. Betting on a future drawdown that may never materialize while slowing near-term emissions cuts is a form of climate risk that models can accommodate on paper but that the atmosphere cannot forgive in practice.
Who Owes What When Temperatures Overshoot?
As overshoot shifts from a worst-case to a central expectation, questions of responsibility and liability move to the forefront. If wealthy, high-emitting countries and corporations continue to delay deep cuts while relying on speculative future CDR, they effectively commit others to living through the heightened risks of an overheated world. This raises thorny issues for international climate negotiations: how to allocate the costs of adaptation, loss and damage, and potential large-scale removal efforts in a way that reflects historical emissions and capacity to pay. The more prolonged the overshoot, the higher those costs become, and the more acute the moral hazard if actors that benefited most from fossil fuel use attempt to offload the consequences onto future generations or less-developed nations.
Designing fair climate policy in an overshoot world therefore requires more than setting a distant net zero date. It demands explicit limits on acceptable overshoot and clear plans for staying within them, backed by near-term milestones for emissions cuts across all major sectors. It also calls for robust governance of CDR, ensuring that any large-scale deployment does not undermine food security, biodiversity, or local communities. Most of all, it requires reframing net zero as a floor rather than a ceiling for ambition: the sooner global emissions fall, and the shorter and shallower any overshoot, the more room remains to preserve critical ecosystems, protect vulnerable populations, and keep open the possibility of a climate future that is challenging but still manageable.
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*This article was researched with the help of AI, with human editors creating the final content.
