The global effort to limit warming to 1.5°C above pre-industrial levels remains the cornerstone of international climate policy and is seen as both a legal and ethical imperative. However, the reality of emissions greenhouse gas emissions shows that this effort faces serious time constraints. Anthropogenic warming is currently around 1.4°C and average global temperatures are rising at a rate of around 0.25°C per decade. If this trend continues, we will exceed the 1.5°C limit within the next few years, with the World Meteorological Organization (WMO) estimating a probability of exceeding this limit between 2026 and 2030 of up to 75 %.

Current national climate plans and government pledges (NDCs) suffer from a significant emissions gap. Even in the most optimistic scenario – if all national plans were fully implemented and additional net-zero emissions targets were met – global warming is projected to peak at around 1.8°C. Under current policies, the median estimate of warming by 2100 is as high as 2.6°C.

Therefore, the main policy challenge shifts from simply avoiding exceeding the limit to directly navigating the era of so-called overshoot. This scenario involves four key stages: exceeding the limit (exceedance), peak and stabilization stage at maximum temperature (plateauing), decline phase a final stabilization below the 1.5°C limit.

Consequences of Overshooting: Why No Overshooting Is Safe

The idea that temporarily exceeding the 1.5°C limit is acceptable or safe is a dangerous fallacy; there are no favorable scenarios for a world with temperatures above this limit. Global risks and impacts do not increase linearly with increasing temperature, but exponentially, and tend to be interconnected and cascading.

The most dramatic changes will affect the Earth's cryosphere. Since the 1970s, more than 40 % of total glacier loss has occurred in the last decade, with 6 % of total volume lost in 2023 alone. If global warming reaches levels close to 3°C, mountain glaciers could lose more than a quarter of their mass by 2100, raising global ocean levels by 9 to 12.5 cm and sea levels by 12.5 cm, permanently altering the availability of freshwater for billions of people dependent on seasonal melting. In the Arctic and Antarctic, sea ice reached a historic low in 2025.

At the same time, warming above 1.5°C threatens to trigger irreversible tipping points in planetary systems. These include the collapse of the West Antarctic and Greenland ice sheets, the weakening or cessation of the Atlantic Meridional Circulation (AMOC), and the death of the Amazon rainforest due to drought and deforestation. These changes would forever alter global climate patterns.

Along with ecological collapse come threats to human society. Without effective adaptation, global food production is projected to decline by up to 14 % by 2050. Extreme heat will threaten the health of populations and the productivity of workers, especially in the informal sectors of developing countries. There are also threats of more frequent epidemics caused by changing pathogen ranges and more frequent transmission of diseases from animals to humans.

The road to recovery: The concept of "overshoot, peak and decline"„

Reversing global warming and successfully returning to below 1.5°C is theoretically possible, but it requires unprecedented efforts in two areas: achieving global net negative CO₂ emissions and deep reductions in emissions of other greenhouse gases, particularly methane.

Physically, temperatures will stabilize only when net global CO₂ emissions fall to zero. But to start reducing temperatures, we need to move to a point where humanity, faced with zero emissions, can actively remove more carbon dioxide from the atmosphere than it puts into it. To reduce the global average temperature by just 0.1°C, it is necessary to achieve approximately 220 billion tons (GtCO₂) net cumulative removal of carbon from the atmosphere. At current emissions, where humanity produces around 40 GtCO₂ per year (from fossil fuels and industry alone in 2024), we would exhaust the remaining carbon budget for 1.5°C in around three years.

Rapid reductions of short-lived pollutants such as methane, mainly from agriculture and waste management, are an extremely important complementary tool. Reducing residual methane emissions by an additional 60 to 70 million tonnes per year after peaking would have the same cooling effect on temperature over the next 50 to 100 years as removing an additional 220 GtCO₂ through technology.

Carbon Dioxide Removal (CDR) Options and Limits

All modelled scenarios that aim to return below 1.5°C will require Carbon Dioxide Removal (CDR) technologies and methods. CDR falls into two main categories:

1. Conventional methods: primarily afforestation, restoration of degraded ecosystems and soil carbon storage. These methods have enormous benefits for biodiversity and local communities, but they carry a high risk of reversal of storage (e.g. in the event of forest fires or drought) and are limited by land availability. At the current rate of afforestation (approximately 2.2 GtCO₂ per year), it would take 100 years to reduce temperatures by 0.1°C, even if fossil fuel emissions were completely zero.
2. New technological methods (novel CDR): these include bioenergy combined with carbon capture and storage (BECCS), direct air capture and geological storage (DACCS), biochar, and accelerated rock weathering. Although these methods offer more durable storage, they currently account for less than 0.1 % of conventional CDR.

However, the massive deployment of CDR has serious limits. Carbon storage in sedimentary basins is limited – the estimated global capacity is below 1500 GtCO₂. If emissions were to remain at 10 GtCO₂ per year after 2050, this capacity would be exhausted by 2200 just to maintain net zero emissions. Technologies such as DACCS are extremely energy-intensive and expensive (US$100–600 per tonne of CO₂), while BECCS requires millions of hectares of land, creating a direct conflict with food production and biodiversity conservation. Moreover, over-reliance on future CDR represents a serious moral hazard that shifts the burden to future generations and weakens the incentive to reduce emissions today.

Adaptation in the era of overshoot: A joint approach with mitigation

Mitigation and adaptation can no longer be seen in isolation; they are mutually supportive and interconnected pillars of a resilient society. Weak mitigation leads to more extreme climate damage, forcing countries to shift scarce funds from long-term development projects to reactive crisis management.

Previous adaptation has often been reactive, partial and incremental, which increases the risk of so-called maladaptation (incorrect adaptation that only shifts or increases vulnerability). In an era of temporary temperature extremes, it is essential transformational adaptation. It changes the fundamental attributes of the socio-ecological system, including technologies, economic structures, paradigms, values, and governance.

This process must take place in three interconnected phases:

• Immediate response phase: aimed at protecting the most vulnerable groups of the population and rapidly reducing emissions.
• Coping and containment phase: stabilizing warming, advancing deep decarbonization, and building infrastructure resilience beyond current limits.
• Long-term resilience phase: managing permanent legacy damage (e.g. rising sea levels), constantly re-evaluating planning baselines (re-baselining) and managing the gradual decline in temperatures.

Justice and climate debt

The concept of a temporary temperature exceedance poses fundamental questions of global justice, power, and political legitimacy for humanity. The climate crisis is impacting the world asymmetrically. The greatest burden is borne by those who have contributed the least to historical emissions – especially small island developing states (SIDS) and least developed countries. For SIDS such as Tuvalu and Kiribati, rising sea levels are not a distant future problem; their agricultural land and groundwater supplies are already facing salinization today.

When adaptation hits its hard limits, we cross the boundary of adaptation and enter the realm of Loss and Damage. The loss of territory, sovereignty or cultural heritage due to the flooding of islands is not reversible by a decrease in global temperatures. The creation and, in particular, the filling of the Loss and Damage Fund with real capital is therefore a key step that the international community must take before the temperature peak is reached.

Countries with the greatest historical responsibility and economic capacity must bear the greatest share of both mitigation and financing for global adaptation. Time is running out. While a return to below 1.5°C is scientifically conceivable, it is not guaranteed. The decisions we make today and in the coming years will determine whether we retain a chance to reverse warming and secure a habitable planet for future generations. JRi&CO2AI 

Source: A message UNEP  entitled Limiting Overshoot Spotlight Report