Ocean heat and reef loss that overlaps stress on the Atlantic circulation and the Amazon
A conditional statement under stated assumptions, never a prediction.
Contents
- ·Edition home
- ·Executive summary
- 1Pressure builds across the system
- 2Key findings
- 3Systems and sectors at baseline
- 4Risks and capability
- 5Ocean heat and reef loss that overlaps stress on the Atlantic circulation and the Amazon
- 6Readings from the other desks
- 7The 2027 agenda
- 8Systems in depth
- AMethodology
- BData appendix
- CReferences and record
- ·Complete edition, for print
5.1Assumptions
Scenario SCN-SR09-CMP-01: what is assumed, and what is held constant.
- Baseline
- the 2026 reference state in this edition
- Drivers
- continued warming near 1.5 degrees C with a strong marine heatwave and a severe Amazon drought in the same decade
- Analogues
- reef mortality, 2025 report7; marine heatwave of 202345
- Interventions
- none modelled: the specification describes the unmitigated case
- Run state
- narrative specification; quantified run scheduled for 2027
5.2The cascade, step by step
- 1
CLI → BIO
ocean heat drives widespread reef bleaching and mortality
2025
- 2
CLI → CLI
a weaker Atlantic circulation shifts rainfall and temperature in Europe, Africa and South America
2023 · 2025
- 3
BIO → WAT
drought and fire raise forest disturbance and reduce moisture recycling
2024
- 4
WAT → FOO
harvests fall where rain shifts and water stress rises
2025
- 5
BIO → FIN
fisheries, tourism and coastal protection lose value
2025
- 6
FIN → CLI
losses strain budgets for adaptation and mitigation
2025
5.3The scenario as a table of steps
How the shock in scenario SCN-SR09-CMP-01 would travel through Planetary Boundaries and Earth-System Tipping Risk’s coupled systems, step by step, under the assumptions the edition states.
| Step | What happens | Source |
|---|---|---|
| 01 Climate to biodiversity | Ocean heat drives widespread reef bleaching and mortality. Analogue or source: 2025. | Edition SR-09, scenario SCN-SR09-CMP-01, step 1 |
| 02 Climate to climate | A weaker Atlantic circulation shifts rainfall and temperature in Europe, Africa and South America. Analogue or source: 2023 · 2025. | Edition SR-09, scenario SCN-SR09-CMP-01, step 2 |
| 03 Biodiversity to water | Drought and fire raise forest disturbance and reduce moisture recycling. Analogue or source: 2024. | Edition SR-09, scenario SCN-SR09-CMP-01, step 3 |
| 04 Water to food | Harvests fall where rain shifts and water stress rises. Analogue or source: 2025. | Edition SR-09, scenario SCN-SR09-CMP-01, step 4 |
| 05 Biodiversity to finance | Fisheries, tourism and coastal protection lose value. Analogue or source: 2025. | Edition SR-09, scenario SCN-SR09-CMP-01, step 5 |
| 06 Finance to climate | Losses strain budgets for adaptation and mitigation. Analogue or source: 2025. | Edition SR-09, scenario SCN-SR09-CMP-01, step 6 |
A teaching model of a conditional scenario under the edition’s stated assumptions: not a forecast, not a prediction and not a warning. Sources: Planetary Boundaries and Earth-System Tipping Risk 2026, scenario SCN-SR09-CMP-01 (2026); Planetary Boundaries and Earth-System Tipping Risk 2026, references (NR-CIT-1) (2026).
Notes
Numbers are the edition’s reference numbers, so a note reads the same in every chapter. The full list, with every source and its licence, is in Annex C. Annex C, references
- 7Lenton, T.M. et al. (eds.), Global Tipping Points Report 2025 (release page read, not the full report; 10 October 2025; coral reef threshold central estimate 1.2 degrees C, range 1 to 1.5). University of Exeter, Exeter. Observation year 2025. Accessed 2026-11-03.back
- 45Drivers of the extreme North Atlantic marine heatwave during 2023, Nature 642(8068), 636 to 643, 2025 (authors not recorded here; bibliographic record and abstract read; no figure used). Observation year 2023. Accessed 2026-11-03.back