UNEP “Limiting Overshoot” Report

Why in News?

The United Nations Environment Programme (UNEP) has released a report titled “Limiting Overshoot: Navigating Exceedance of 1.5°C and Pathways Towards Return.” The report states that a temporary breach of the 1.5°C global-warming threshold under the Paris Agreement is increasingly inevitable in the near term.

The report proposes an “overshoot, peak and decline” framework to limit peak warming and enable a multi-decadal return towards safer planetary boundaries.

Key Findings

Imminent Breach of 1.5°C

Human-induced global warming has reached approximately 1.4°C above pre-industrial levels, increasing at around 0.25°C per decade. Operational decadal forecasts indicate a 75% probability that the five-year mean temperature will exceed 1.5°C during 2026–2030.

Remaining Carbon Budget

To retain a 50% chance of limiting warming to 1.5°C, the remaining carbon budget is estimated at around 130 billion tonnes of CO₂ from 2026 onwards. At current emissions of approximately 40 billion tonnes of CO₂ annually, this budget could be exhausted in about three years.

Cost of Delay

Every additional five years of sustained high emissions could add approximately 0.1°C to peak warming. Emissions since 2015 have already increased the minimum achievable peak warming by approximately 0.2°C.

Emissions and Implementation Gap

Under current policies, median projected global warming could reach 2.6°C by 2100, with a range of 1.9°C–3.6°C. Even if all current NDCs and long-term Net-Zero targets are fully implemented, central peak warming is projected at 1.8°C.

Why Methane Reduction is Important

• The report identifies methane mitigation as an important near-term climate action. Methane currently contributes around 0.5°C to global warming.

• Because methane has a relatively short atmospheric lifetime, reducing methane emissions can slow the rate of warming more rapidly than equivalent CO₂ reductions. While reducing oil and gas leaks is relatively feasible, reducing methane from agriculture and waste remains more challenging.

• The Global Methane Pledge, launched at COP26 by the European Union and the United States, has been joined by more than 155 countries and aims to reduce anthropogenic methane emissions by at least 30% from 2020 levels by 2030.

“Overshoot, Peak and Decline” Pathway

• The proposed framework shifts climate strategy from merely trying to prevent a 1.5°C breach towards actively managing the consequences of an overshoot.

• Overshoot: Global warming exceeds the 1.5°C threshold but has not yet reached its peak.

• Peak/Plateau: Warming reaches its maximum level above 1.5°C and begins to stabilize.

• Decline: Global temperatures gradually decline from the peak as a result of global net-negative emissions.

• Stabilization: Temperatures eventually return to or below the 1.5°C target and stabilize at that level.

Consequences of Climate Overshoot

Climate overshoot could produce long-lasting and potentially irreversible impacts.

Cryosphere: Glaciers outside Greenland and Antarctica could lose 25–40% or more of their mass by 2100, contributing approximately 9–15.4 cm to sea-level rise.

Sea-Level Rise: Sea levels will continue rising for centuries to millennia because of deep-ocean warming and ice-sheet inertia. Every 100 years above 1.5°C could commit the world to approximately 40 cm of additional median sea-level rise by 2300.

Oceans: Ocean acidification and deoxygenation can persist for centuries because recovery of deep-ocean circulation and chemistry is extremely slow.

Food Security: Global food production could decline by up to 14% by 2050 without effective adaptation.

Earth-System Tipping Points

The report highlights risks to major Earth-system components, including weakening of the Atlantic Meridional Overturning Circulation (AMOC), potential transformation of the Amazon rainforest from a carbon sink to a carbon source, and irreversible retreat of parts of the West Antarctic Ice Sheet.

UNEP Recommendations

• The report calls for rapid and deep reductions in CO₂ and methane emissions, expansion of renewable energy, responsible deployment of carbon dioxide removal (CDR), stronger Loss and Damage finance, protection of natural ecosystems and stronger climate-resilience measures.

• It recommends increasing renewables to 60–70% of global electricity generation by 2030, supported by grid expansion, energy storage and demand flexibility.

• The report also emphasizes that carbon dioxide removal should complement, not replace, aggressive emission reductions, with appropriate governance to manage environmental and land-use risks.