Toute l'actualitéPublished on 2 September 2026, the United Nations Environment Programme (UNEP) report Limiting Overshoot examines the consequences of the expected overshoot of 1.5°C and the conditions under which temperatures could eventually return below this threshold. It underscores the urgency of cutting emissions to net zero—an essential milestone before sustained net-negative emissions can enable temperatures to decline—while simultaneously strengthening adaptation. For companies and investors engaged in Nature-based Solutions, the report highlights ecosystem resilience as a prerequisite for their long-term contribution to climate action. Drawing on these findings, Reforest’Action more broadly advocates for Nature-based Solutions to be designed, assessed and financed with the long-term durability of their climate, ecological and social benefits firmly in mind.
1.5°C: Limiting the Magnitude and Duration of Overshoot
UNEP finds that efforts to reduce greenhouse gas emissions have not been sufficient to avoid global warming exceeding 1.5°C above pre-industrial levels, with this overshoot now expected within the next few years. This is no longer simply a matter of individual years temporarily exceeding 1.5°C: long-term global warming, measured over multiple decades, is now expected to cross this threshold.
The objective of limiting global warming to 1.5°C nevertheless remains critical. Every fraction of a degree avoided and every year by which overshoot is shortened can reduce impacts on biodiversity and ecosystems, infrastructure and human societies. Nor would a subsequent decline in global warming erase all the damage incurred: some biodiversity losses and ecosystem transformations would be irreversible, while sea-level rise would continue over the long term.
The report therefore proposes viewing the crossing of 1.5°C as a trajectory that could unfold over several decades: exceedance, peak warming, followed potentially by temperature decline and stabilization. The magnitude of the peak and the length of exposure to higher temperatures will determine the severity of the impacts. The prospect of returning below 1.5°C, meanwhile, remains deeply uncertain. The report estimates that around 220 GtCO₂ of cumulative net-negative emissions would be required to lower global temperatures by approximately 0.1°C. Even if net-negative emissions reached 10 GtCO₂ per year, cooling would amount to only around 0.05°C per decade. In other words, the warming accumulated over one decade at the current rate could take several decades to reverse, even under highly ambitious assumptions for carbon dioxide removal. UNEP therefore reiterates that carbon dioxide removal must complement deep emissions reductions, not substitute for them.
In this context, mitigation and adaptation must advance together. Limiting warming reduces future risks but does not eliminate the need for adaptation; strengthening resilience, in turn, helps preserve the conditions required to sustain climate action.
This interdependence should also inform the companies financing Nature-based Solutions. Whether they contribute directly to ecosystem restoration or support certified carbon projects, the same question arises: how should these projects be designed, financed and supported so that the intended benefits can materialize and endure in a changing climate?
Safeguarding the Contribution of Ecosystems in a Changing Climate
UNEP notes that the most ambitious scenarios envisage substantial volumes of net-negative emissions in the second half of the century, even as global warming may weaken natural carbon sinks. The ecosystems relied upon to mitigate climate change and support territorial adaptation are themselves vulnerable to its impacts: drought, heat stress, wildfires and pests can reduce their capacity to absorb carbon and trigger the release of previously stored carbon.
The issue extends beyond carbon. The report also highlights that some ecosystem-based adaptation measures could reach their limits beyond 1.5°C. Shifting climatic conditions suitable for individual species may drive their redistribution and reshape ecological communities, requiring existing protection frameworks to be reconsidered and ecological connectivity across landscapes to be strengthened. The ability of Nature-based Solutions to deliver durable outcomes therefore depends on the resilience of the ecosystems on which they rely.
Project Robustness Starts with Ecological Relevance
A sequestration potential, a habitat restoration objective or an ambition to protect water resources must be assessed in light of the territory in which the project is embedded, the risks that could compromise delivery, and the measures in place to address them. For a project developer, this means identifying which ecosystems should be protected or restored, anticipating climatic and hydrological constraints, and accounting for local land uses. The project response should emerge from this diagnosis rather than from an acreage or sequestration target defined independently of the territory.
From this perspective, biodiversity and water-resource conservation, as well as socioeconomic impacts for communities, should not be viewed solely as co-benefits associated with a carbon sequestration project. These different dimensions can constitute the primary purpose of a contribution and be recognized and valued in their own right.
The same attention to project context must extend to governance. UNEP emphasizes that equity is integral to the feasibility and legitimacy of climate pathways. At project level, participation in decision-making, the protection of rights and benefit-sharing should therefore be embedded from the outset.
Project design consequently requires clarity on the impacts being pursued, an understanding of how they interact, and safeguards to ensure that pursuing one objective does not undermine other ecosystem functions.
Taking a Long-Term View of Financing
Time is a critical dimension of ecosystem-based adaptation. Many measures require long lead times to reach maturity, even as exposure to climate hazards increases. Delaying their implementation reduces both their effectiveness and their feasibility. Financing decisions must therefore enable sufficiently early action while reflecting the specific time horizon of each project.
For companies financing these projects, this means looking beyond the initial intervention. Maintenance, management, results monitoring and any necessary adjustments must be anticipated from the design stage, together with the resources and responsibilities associated with them. They are part of the conditions required both to deliver the intended benefits and to sustain them over time.
This long-term perspective must also be accompanied by rigorous impact measurement. Each project should be monitored against its own objectives, distinguishing activities undertaken from effects actually observed. For carbon, this means, in particular, differentiating projected removals from those actually achieved and verified. For ecological restoration, monitoring may focus on changes in habitats, ecological functions or ecosystem services, using appropriate indicators. Different project purposes therefore call for tailored monitoring approaches, underpinned by the same requirement for transparency.
Finally, a long-term perspective requires projects to be designed with the capacity to adjust. Who monitors evolving risks? Who can decide that practices need to change? What resources can be mobilized if conditions diverge from initial assumptions? In this respect, UNEP stresses the need to connect observation, learning and the revision of decisions so that action can evolve alongside changing knowledge and conditions. The objective is not to demand risk-free projects, but projects in which risks are made explicit and actively managed.
UNEP’s report highlights both the lasting consequences of overshooting 1.5°C and the profound uncertainty surrounding any eventual return below this threshold. Yet the decisions taken today remain decisive in limiting the magnitude and duration of overshoot and reducing the resulting damage. Rapid emissions reductions, the protection of natural carbon stocks, the responsible development of carbon dioxide removal capacity and stronger adaptation remain complementary levers. For actors involved in Nature-based Solutions, the challenge is to fully embed ecosystem resilience into project design, financing and monitoring. Accounting for the risks to which ecosystems are themselves exposed is essential to preserving their capacity to make a lasting contribution to both mitigation and adaptation.