Introduction

The Paris Agreement established the global objective of limiting warming to well below 2 °C above pre‑industrial levels, while pursuing efforts to restrict the temperature increase to 1.5 °C. The 1.5 °C threshold remains central to climate policy because surpassing it significantly heightens the risk of irreversible ecosystem loss, extreme weather intensification, sea‑level rise, and large‑scale human displacement.

A key concept underpinning this goal is the remaining carbon budget—the total amount of carbon dioxide that can still be emitted while maintaining a given probability of staying below 1.5 °C. Because CO₂ accumulates in the atmosphere over centuries, this budget is finite and rapidly shrinking. By early 2026, scientific assessments show that the remaining budget has become critically small, placing the world on the brink of exhausting its allowance within only a few years. Understanding the dynamics of this budget and the implications of its depletion is essential for shaping effective climate action in the years ahead.

The Scientific Basis of the Carbon Budget

The carbon budget is derived from the relationship between cumulative CO₂ emissions and global temperature rise. Since CO₂ is long‑lived, the total amount emitted over time is the primary driver of long‑term warming. Climate models and observational data allow scientists to estimate how much additional CO₂ can be released while still keeping warming below 1.5 °C with varying levels of probability.

By 2020, the remaining budget for a 50% chance of staying below 1.5 °C was estimated at roughly 500 GtCO₂, with a significantly smaller allowance for higher confidence levels. However, global emissions remained high throughout the early 2020s, averaging around 40 GtCO₂ per year. As a result, the remaining budget has declined sharply.

By January 2026, updated assessments indicate that the remaining carbon budget for a 50% chance of limiting warming to 1.5 °C is approximately 130 GtCO₂. At current emission rates, this budget is expected to be fully exhausted in just over three years. This means that even under optimistic mitigation scenarios, the world is extremely close to surpassing the 1.5 °C threshold.

Current Trajectory and Rate of Depletion

The rapid depletion of the carbon budget reflects the continued global dependence on fossil fuels for electricity generation, transport, industry, and heating. Although renewable energy capacity has expanded significantly, global emissions have not yet entered the steep and sustained decline required to preserve the remaining budget.

Following the temporary emission reductions during the COVID‑19 pandemic, global fossil fuel use rebounded strongly. Emissions in 2024 and 2025 reached record highs, driven by increased energy demand, industrial recovery, and continued investment in oil and gas infrastructure.

Every ton of CO₂ emitted today directly reduces the remaining budget. Large‑scale fossil fuel projects approved in recent years effectively consume multiple years of the remaining allowance in a single decision. If emissions continue at their current pace, the remaining budget will be exhausted before the end of the decade. If emissions increase further, exhaustion will occur even sooner.

This trajectory underscores a stark reality: incremental policy adjustments are no longer sufficient. Only rapid, transformative decarbonization-across all sectors and regions-can alter the current path and preserve any remaining chance of limiting warming to 1.5 °C.

Implications of Overshooting the 1.5 °C Threshold

The exhaustion of the remaining carbon budget does not imply that global warming halts the moment the final allowable ton of CO₂ is emitted. Instead, it marks the point at which the likelihood of surpassing the 1.5 °C limit during the 21st century becomes extremely high. This leads to what is known as an overshoot scenario, in which global temperatures temporarily rise above 1.5 °C-potentially reaching 1.6 °C or 1.7 °C-before stabilising or gradually declining if global emissions eventually fall to net‑zero and atmospheric CO₂ is actively reduced.

The consequences of such an overshoot are profound. Scientific modelling consistently shows that climate risks increase sharply and non‑linearly beyond 1.5 °C. Approaching 2 °C significantly heightens the probability of crossing major tipping points, including destabilisation of the West Antarctic Ice Sheet, accelerated loss of Arctic summer sea ice, and large‑scale dieback of the Amazon rainforest. Even a temporary rise above 1.5 °C can lock in long‑term impacts, such as higher sea levels driven by thermal expansion and irreversible ice melt-processes that unfold over centuries and cannot be reversed simply by later cooling.

Short‑term overshoot also disrupts global weather patterns. Regions dependent on stable rainfall may experience prolonged droughts, while others face intensified monsoon seasons or more frequent extreme storms. These disruptions carry immediate humanitarian, agricultural, and economic consequences. The central message embedded in the 1.5 °C target is that every fraction of a degree matters, and overshoot amplifies risks that compound across ecosystems, societies, and generations.

The Role of Carbon Dioxide Removal (CDR) in Budget Management

As the remaining carbon budget shrinks, Carbon Dioxide Removal (CDR) becomes increasingly prominent in discussions about achieving or restoring alignment with the 1.5 °C pathway. CDR encompasses a spectrum of natural and technological approaches designed to extract CO₂ from the atmosphere and store it securely over long timescales. These include afforestation, soil carbon enhancement, mineral weathering, bioenergy with carbon capture and storage (BECCS), and direct air capture with geological storage.

However, the growing reliance on CDR introduces significant uncertainties. Most large‑scale CDR technologies remain expensive, energy‑intensive, and unproven at the scale required to meaningfully counterbalance global emissions. Land‑intensive approaches such as BECCS risk competing with food production and biodiversity conservation. Over‑reliance on future CDR capacity effectively delays necessary mitigation today, creating a dangerous assumption that future technologies will compensate for present inaction.

If CDR deployment fails to expand at the required pace, or if its real‑world performance falls short of expectations, the world will face higher levels of warming with limited options for correction. For this reason, CDR must be treated as a complement to rapid emissions reductions, not a substitute. The remaining carbon budget should be prioritised for direct mitigation, reserving CDR primarily for neutralising residual emissions from sectors where decarbonisation is technically or economically challenging.

Policy Responses to Budget Constraints

The rapid depletion of the carbon budget demands a shift from aspirational climate commitments to binding, enforceable policies that deliver immediate and sustained emissions reductions. Achieving this requires a comprehensive transformation of energy systems, industrial processes, transport networks, and land‑use practices.

Governments must strengthen their national climate commitments to align with a 1.5 °C‑compatible trajectory, which requires global emissions to peak immediately and decline steeply throughout the 2020s. This involves accelerating the deployment of renewable energy, phasing out coal and limiting new oil and gas development, and implementing stringent efficiency standards across buildings, vehicles, and industry.

Carbon pricing—through taxes or cap‑and‑trade systems-remains a critical tool for embedding the true cost of emissions into economic decision‑making. Investment in electric mobility, grid modernisation, and large‑scale energy storage is essential to support the transition. Equally important is ensuring a just transition, providing support, retraining, and economic diversification for workers and communities historically dependent on fossil fuel industries.

Delays in policy implementation dramatically reduce the remaining budget and force more abrupt and disruptive transitions later. The political challenge lies in overcoming entrenched interests, aligning short‑term economic incentives with long‑term climate stability, and ensuring that the benefits of decarbonisation are shared equitably.

Conclusion

The near‑exhaustion of the carbon budget for limiting warming to 1.5 °C stands as one of the defining scientific realities of early 2026. The shrinking atmospheric allowance leaves no space for gradualism or incremental progress. Every ton of CO₂ emitted today narrows the pathway for future generations and increases the likelihood of irreversible climate impacts.

While carbon dioxide removal may play a role in correcting overshoot, it cannot justify continued high emissions in the present. Respecting the 1.5 °C limit requires immediate global cooperation to halt fossil fuel expansion, accelerate the decarbonisation of energy systems, and implement policies that reflect the urgency of the moment.

Bibliography

Anderson, Kevin & Broderick, John. Navigating the Climate Crisis: Honesty, Responsibility and Action.

Archer, David. The Long Thaw: How Humans Are Changing the Next 100,000 Years of Earth’s Climate.

Geden, Oliver & Schenuit, Felix. Carbon Dioxide Removal: Governance, Policy, and Ethics.

Hansen, James. Storms of My Grandchildren: The Truth About the Coming Climate Catastrophe.

Hickel, Jason. Less Is More: How Degrowth Will Save the World.

Klein, Naomi. This Changes Everything: Capitalism vs. the Climate.

Lenton, Timothy & Latour, Bruno. Earth System Boundaries: Tipping Points and Planetary Futures.

Mann, Michael E. The New Climate War: The Fight to Take Back Our Planet.

Rockström, Johan & Klum, Mattias. Big World, Small Planet: Abundance Within Planetary Boundaries.

Steffen, Will & Richardson, Katherine. Earth System Science: A Very Short Introduction.

Wallace-Wells, David. The Uninhabitable Earth: Life After Warming.

Wong, Phoebe & Matthews, Damon. Carbon Budgets and Climate Futures: Understanding the Path to 1.5°C.

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