UNEP Sets Out Overshoot Pathway as Global Warming Limit Breach Becomes Inevitable

Global Warming Limit Latest News

• The United Nations Environment Programme has, for the first time, set out a detailed “overshoot, peak, and decline” pathway, warning that a breach of the 1.5°C global warming limit is now unavoidable.

Background: The 1.5°C Goal

• The Paris Agreement of 2015 set the central goal of limiting the rise in average global temperatures to 1.5°C above pre-industrial levels, with a broader ceiling of well below 2°C.
• The 1.5°C figure was not arbitrary. Scientific assessments have repeatedly shown that beyond this threshold, the risks of severe heatwaves, coral reef collapse, ice sheet destabilisation and food system disruption rise sharply.
• The diplomatic groundwork for accepting that this limit may be breached was laid at COP30, held in 2025 in Belém, Brazil. 
• The consensus decision there, described as the “Global Mutirão” or collective effort, became the first COP text to concede that a temporary overshoot of 1.5°C was likely, given how rapidly the remaining carbon budget was being consumed.

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The UNEP Report

• The report, titled Limiting Overshoot, states that global warming will cross 1.5°C “in the next few years”.
• Its projections are sobering. Even in a scenario where every country delivers on its national climate plan and net-zero target, peak warming would reach 1.8°C. 
• Based on current policies, the world is heading towards a rise of about 2.6°C by 2100, within a range of 1.9°C to 3.6°C.

What the Pathway Involves

• The pathway projects a trajectory in which the world overshoots the 1.5°C target, then seeks to:
  • Hold peak temperatures after the overshoot as low as possible
  • Bring warming back down below 1.5°C by 2100
• This represents a significant shift in framing. Climate policy has until now been organised around avoiding the breach. The new approach accepts the breach as a given and focuses on minimising its magnitude and duration.
• The UN Secretary-General, commenting on the report, noted that recent scorching heat, raging wildfires and deadly floods are a warning of what lies ahead, and that the overshoot must be made “as small and short as possible.”

The Compounding Costs of Overshoot

• The report warns that time spent above 1.5°C carries compounding costs rather than merely temporary discomfort. Specific consequences identified include:
  • Faster sea-level rise
  • Coral reef collapse
  • Glacier loss exceeding a quarter of global mass by 2100
  • Declines of up to 14% in global food production by 2050 without effective adaptation
  • Rising odds of irreversible tipping points
• The tipping points flagged are the West Antarctic and Greenland ice sheets, the Atlantic Meridional Overturning Circulation, and the Amazon. Crossing these thresholds would trigger changes that no adaptation initiative could undo.

Delay Becomes Progressively Costlier

• One of the report’s most important findings concerns the asymmetry between emitting and removing carbon.
• Every five years of continued high emissions adds roughly 0.1°C to peak warming.
• Reversing that same 0.1°C afterwards, however, means pulling about 220 billion tonnes of carbon dioxide back out of the atmosphere, over and above whatever is still being emitted at the time.
• In other words, it becomes progressively harder to roll back the effects of each tonne of carbon released. Delay does not simply postpone action; it multiplies the effort required later.

The New Emphasis on Methane

• In a first for the UN, the report places significant stress on methane.
• Methane contributes about 0.5°C of warming. Because it is a short-lived but highly potent greenhouse gas, cutting methane emissions is described as the most effective way to slow warming in the near term.
• This matters for the overshoot strategy specifically. Reducing carbon dioxide is essential for long-term temperature stabilisation, but methane reduction can lower the peak, which is precisely what the overshoot pathway seeks to minimise.

The Role of Carbon Removal

• The report makes clear that emission cuts alone will no longer suffice.
• Bringing temperatures back below 1.5°C after an overshoot requires actively removing carbon from the atmosphere. 
• As noted by COP30 leadership, this means a steep scaling up of nature-based removals, particularly large reforestation programmes.
• This creates a substantial practical challenge. Carbon removal at the scale implied- hundreds of billions of tonnes- has never been attempted, and nature-based methods require vast land areas, long timeframes and sustained protection against reversal through fire, drought or land-use change.

Implications for Global Climate Policy

• The report signals three shifts in how climate action is likely to be discussed.
• First, the focus moves from avoidance to damage limitation. The question is no longer whether 1.5°C will be crossed but by how much and for how long.
• Second, near-term measures gain priority. With peak warming as the key variable, actions that deliver quick temperature benefits, especially methane cuts, become more valuable relative to slower long-term measures.
• Third, carbon removal moves from the margins to the centre of climate strategy, raising difficult questions about land use, cost, verification and equity.

Source: TH