How Should the World Respond to an Unavoidable Climate Overshoot?

The United Nations Environment Programme’s (UNEP) recent observations have warned that global warming is set to breach 1.5°C within the next few years, making an overshoot unavoidable. UNEP’s proposed “overshoot, peak, and decline” pathway underscores the linkage between emerging risks and the corrective action needed to limit their depth and duration.

Irreversibility and Tipping Points

  • Crossing thresholds like ice-sheet collapse, AMOC disruption, and Amazon dieback creates risks that cannot be reversed on human timescales, undermining the assumption that overshoot is a temporary, correctable phase.
  • This demands front-loaded mitigation: only rapid, sustained emission cuts towards net-zero can minimise peak temperature and shorten exceedance duration, reducing the probability of triggering such thresholds.

Compounding, Non-Linear Impacts

  • Risks to food security, water systems, and coastal settlements do not scale linearly with temperature; each phase of overshoot inherits the legacies of those preceding it, complicating sequenced responses.
  • This calls for integrated mitigation-adaptation planning, prioritising interventions with dual co-benefits, such as passive cooling, so adaptation becomes transformational rather than a residual reaction to accumulating impacts.

The Equity Deficit

  • Historical emitters bear the least immediate exposure, while vulnerable nations, particularly SIDS, face disproportionate, potentially existential impacts.
  • Addressing this requires differentiated, inclusive responsibility, with high-emitting nations acting hardest and fastest, and disproportionately affected countries embedded in global decision-making on loss and damage.

Limits of Technological Fixes

  • Even optimistic Carbon Dioxide Removal (CDR) scaling is unlikely to lower temperatures by more than a few tenths of a degree, while carrying governance and equity risks.
  • This underscores the need for governed supplementation, where CDR strictly complements emission cuts under robust oversight, never substituting for mitigation.

Summing Up
Since overshoot cannot be treated as reversible by default, aligning each structural risk with its calibrated, equity-centred response remains the only credible pathway back towards climate stability.