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Systems in depth

One section per system: its state at evidence close, its exposures and what the operational series will watch.

8 min read0 figures5 tables20 notesNR-STRATEGIC-PLANETARY-GLOBAL-2026-BASELINE

Contents
  1. ·Edition home
  2. ·Executive summary
  3. 1Pressure builds across the system
  4. 2Key findings
  5. 3Systems and sectors at baseline
  6. 4Risks and capability
  7. 5Ocean heat and reef loss that overlaps stress on the Atlantic circulation and the Amazon
  8. 6Readings from the other desks
  9. 7The 2027 agenda
  10. 8Systems in depth
    1. 8.1 Common causes
    2. 8.2 Domino effects
    3. 8.3 Inter-systemic feedbacks
    4. 8.4 Shared vulnerabilities
    5. 8.5 Thresholds and tipping
  11. AMethodology
  12. BData appendix
  13. CReferences and record
  14. ·Complete edition, for print

8.1Common causes

One cause can press on many boundaries at once. Fossil carbon warms the surface and acidifies the ocean, and land conversion presses on forests, water and species.

425.62ppm

global annual mean CO2, 202510

≈37.4GtCO2

fossil CO2 emissions, 2024 (preliminary)11

1.1%

projected rise in fossil CO2 emissions, 202512

Table 8.1Evidence at baseline
InstanceMechanism in actionEvidenceStatus
Fossil carbonCO2 rising each year; record fossil emissions projected for 2025101112Reported
Land conversionabout 75% of land significantly altered15Reported
Fertiliser and nutrientsnitrogen and phosphorus flows above their limits3Reported
Novel entitiesreleases rise faster than assessment capacity22Reported

Pathways in this mechanism

  • ENE → CLI emissions
  • FOO → BIO land and nutrients
  • MIN → BIO extraction

Evidence to bind in 2027

  • shares of each cause by boundary
  • control variable for novel entities

Related editions

  • GLB Global Systems
  • SR-02 Critical Infrastructure and Lifeline Systems
  • SR-06 Insurance, Protection Gaps and Insurability
  • SR-07 Food–Water–Energy Security
  • GS-07 Climate and Earth Systems
  • GS-11 Biodiversity and Ecosystems

8.2Domino effects

Crossing one threshold can raise the odds of crossing the next. The reassessment of climate tipping points states that crossing some of them can increase the likelihood of crossing others.

9core

tipping elements in the 2022 reassessment6

7regional

impact tipping elements in the 2022 reassessment6

10% to 47%

of Amazon forests exposed to compounding disturbances by 205019

Table 8.2Evidence at baseline
InstanceMechanism in actionEvidenceStatus
Ice sheet to ocean circulationGreenland melt would affect the Atlantic circulation6Reported
Reef loss to peoplenearly a billion people and a quarter of marine life depend on reefs7Reported
Forest to waterforest loss reduces moisture recycling1923Inferred
Tipping cascadesinteracting elements raise the risk of climate domino effects3435Inferred

Pathways in this mechanism

  • CLI → BIO
  • BIO → WAT → FOO
  • CLI → CLI ice and ocean

Evidence to bind in 2027

  • cascade strengths between elements
  • timing of knock-on effects

Related editions

  • GLB Global Systems
  • SR-02 Critical Infrastructure and Lifeline Systems
  • SR-06 Insurance, Protection Gaps and Insurability
  • SR-07 Food–Water–Energy Security
  • GS-07 Climate and Earth Systems
  • GS-11 Biodiversity and Ecosystems

8.3Inter-systemic feedbacks

The Earth system amplifies and dampens itself. Heat accumulates, seas rise faster, and natural sinks respond to the carbon and heat they absorb.

0.89W per m²

Earth energy imbalance, 2005 to 202413

4.1mm a year

sea-level rise rate, 2016 to 2025 (2.1 in 1993 to 2002)9

≈7%

more atmospheric moisture per degree C of warming28

Table 8.3Evidence at baseline
InstanceMechanism in actionEvidenceStatus
Heat uptakeenergy imbalance has risen in each 20-year period since 197513Reported
Sea levelrate of rise nearly doubled between 1993 to 2002 and 2016 to 20259Reported
Water cyclewarming adds moisture and intensifies the cycle28Reported
Ocean carbon uptakeabsorbed CO2 acidifies the surface ocean2Reported

Pathways in this mechanism

  • CLI → CLI energy imbalance
  • CLI → WAT water cycle
  • ENE → BIO acidification

Evidence to bind in 2027

  • feedback strengths at global scale
  • sink response under overshoot

Related editions

  • GLB Global Systems
  • SR-02 Critical Infrastructure and Lifeline Systems
  • SR-06 Insurance, Protection Gaps and Insurability
  • SR-07 Food–Water–Energy Security
  • GS-07 Climate and Earth Systems
  • GS-11 Biodiversity and Ecosystems

8.4Shared vulnerabilities

Different boundaries share the same weak points: warm-water reefs, large forests, ice sheets and the people who depend on them.

≈1billion

people who depend on warm-water reefs, nearly7

86%

of the world population with two or more safe and just boundaries exceeded5

85%

of the world population above the proposed just air pollution limit5

Table 8.4Evidence at baseline
InstanceMechanism in actionEvidenceStatus
Reefsthermal threshold passed; many people and species depend on them7Reported
Forestscompounding disturbance projected for large areas19Reported
Unequal exposuremultiple exceedances concentrate where many people live5Reported
Shared data gapsno agreed control variable for chemicals and plastics22Reported

Pathways in this mechanism

  • CLI → BIO reef loss
  • BIO → WAT forest loss
  • BIO → FIN lost services

Evidence to bind in 2027

  • regional exposure maps
  • dependence of livelihoods on specific systems

Related editions

  • GLB Global Systems
  • SR-02 Critical Infrastructure and Lifeline Systems
  • SR-06 Insurance, Protection Gaps and Insurability
  • SR-07 Food–Water–Energy Security
  • GS-07 Climate and Earth Systems
  • GS-11 Biodiversity and Ecosystems

8.5Thresholds and tipping

A system can absorb stress until a threshold is crossed. Boundaries mark where risk rises. Tipping points mark where change can become self-sustaining.

1.2degrees C

central threshold estimate, warm-water reefs7

≈1.5degrees C

central threshold estimate, Greenland and West Antarctic ice sheets6

2.84against 2.86

ocean aragonite saturation against its limit3

Table 8.5Evidence at baseline
InstanceMechanism in actionEvidenceStatus
Boundary limitsseven of nine control variables beyond their limits23Reported
Reef thresholdcentral estimate passed at about 1.4 degrees C of warming7Reported
Ice sheetscentral estimates near 1.5 degrees C with wide ranges6Reported
Atlantic circulationstudies disagree on whether it tips this century161718Reported

Pathways in this mechanism

  • CLI → CLI threshold crossing
  • BIO → BIO reef tipping
  • WAT → WAT circulation

Evidence to bind in 2027

  • threshold ranges at regional scale
  • a long record of circulation strength

Related editions

  • GLB Global Systems
  • SR-02 Critical Infrastructure and Lifeline Systems
  • SR-06 Insurance, Protection Gaps and Insurability
  • SR-07 Food–Water–Energy Security
  • GS-07 Climate and Earth Systems
  • GS-11 Biodiversity and Ecosystems

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

  1. 10NOAA Global Monitoring Laboratory (ed.), Global annual mean CO2 growth data (annual means 2020 to 2025; 425.62 ppm in 2025). NOAA, Boulder. Observation year 2025. Accessed 2026-11-03.back
  2. 11Global Carbon Project (ed.), Global Carbon Budget 2024, Earth System Science Data 17, 965, 2025 (fossil CO2 about 37.4 GtCO2 in 2024; 422.45 ppm projected; remaining 1.5 degrees C budget about 235 GtCO2 from 2025). Global Carbon Project. Observation year 2024. Accessed 2026-11-03.back
  3. 12Global Carbon Project (ed.), Global Carbon Budget 2025 (landing page: projected 1.1% rise in fossil CO2 emissions, a record high; headline tables not read). Observation year 2025. Accessed 2026-11-03.back
  4. 15IPBES (ed.), Global Assessment Report on Biodiversity and Ecosystem Services (media release of 6 May 2019: around one million species threatened; about 75% of land and 66% of marine environment significantly altered). IPBES Secretariat, Bonn. Observation year 2019. Accessed 2026-11-03.back
  5. 3Globaia (ed.), Planetary boundaries status dashboard (nine boundaries with control-variable values and limits; page last updated 15 June 2026; its summary text still says six while its table shows seven). Observation year 2025. Accessed 2026-11-03.back
  6. 22Outside the Safe Operating Space of the Planetary Boundary for Novel Entities, Environmental Science and Technology 56(3), 1510 to 1521, 2022 (abstract read). Observation year 2022. Accessed 2026-11-03.back
  7. 6Armstrong McKay, D.I., Staal, A., Abrams, J.F. et al., Exceeding 1.5°C global warming could trigger multiple climate tipping points, Science 377, eabn7950, 2022 (full text read; nine core and seven regional tipping elements). Observation year 2022. Accessed 2026-11-03.back
  8. 19Critical transitions in the Amazon forest system, Nature 626, 555 to 564, 2024 (authors not recorded here; abstract read: 10% to 47% of forests exposed to compounding disturbances by 2050). Observation year 2024. Accessed 2026-11-03.back
  9. 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
  10. 23Wang-Erlandsson, L. et al., A planetary boundary for green water, Nature Reviews Earth and Environment 3(6), 380 to 392, 2022 (bibliographic record read, no abstract; no figure taken from it). Observation year 2022. Accessed 2026-11-03.back
  11. 34UNVERIFIED, not opened: Wunderling, N. et al., Interacting tipping elements increase risk of climate domino effects under global warming, Earth System Dynamics 12, 601 to 619, 2021, cited from memory. Observation year 2021. Accessed 2026-11-03.back
  12. 35UNVERIFIED, not opened: Rocha, J.C., Peterson, G., Bodin, O. and Levin, S., Cascading regime shifts within and across scales, Science 362, 1379 to 1383, 2018, cited from memory. Observation year 2018. Accessed 2026-11-03.back
  13. 13Indicators of Global Climate Change 2024, Earth System Science Data 17, 2641, 2025 (2015 to 2024 average 1.24 degrees C; 2024 at 1.52; human-induced 1.36; energy imbalance 0.89 W per m² for 2005 to 2024). Observation year 2024. Accessed 2026-11-03.back
  14. 9WMO (ed.), State of the Climate 2025 Update for COP30 (January to August 2025 at 1.42 degrees C; CO2 423.9 ppm in 2024; sea-level rise 4.1 mm a year, 2016 to 2025). World Meteorological Organization, Geneva. Observation year 2025. Accessed 2026-11-03.back
  15. 28Global Commission on the Economics of Water (ed.), Turning the Tide: A Call to Collective Action, release page of 17 March 2023 (about 7% more atmospheric moisture per degree C of warming). Observation year 2023. Accessed 2026-11-03.back
  16. 2Sakschewski, B., Caesar, L., Rockström, J. et al., Planetary Health Check 2025: A Scientific Assessment of the State of the Planet (publication page; seven of nine boundaries breached). Planetary Boundaries Science, Potsdam. Observation year 2025. Accessed 2026-11-03.back
  17. 5Rockström, J. et al., Safe and just Earth system boundaries, Nature 619, 102 to 111, 2023 (seven of eight globally quantified boundaries exceeded; 52% of land and 86% of population with two or more exceeded). Observation year 2023. Accessed 2026-11-03.back
  18. 16Baker, J. et al., Continued Atlantic overturning circulation even under climate extremes, Nature 638, 987 to 994, 2025 (34 models; collapse this century judged unlikely; weakening still expected; abstract and Met Office release read). Observation year 2025. Accessed 2026-11-03.back
  19. 17van Westen, R.M., Kliphuis, M. and Dijkstra, H.A., Physics-based early warning signal shows that AMOC is on tipping course, Science Advances 10, eadk1189, 2024 (full text read). Observation year 2024. Accessed 2026-11-03.back
  20. 18Ditlevsen, P. and Ditlevsen, S., Warning of a forthcoming collapse of the Atlantic meridional overturning circulation, Nature Communications 14, 4254, 2023 (abstract read: collapse estimated around mid-century; a 2025 erratum is listed and was not read). Observation year 2023. Accessed 2026-11-03.back

Cite this chapter

Valadbaygi, S. (Ed.). (2026). Chapter 8: Systems in depth. In Strategic Systems Report 2026: Planetary Boundaries and Earth-System Tipping Risk (Baseline Edition 2026, Report No. NR-STRATEGIC-PLANETARY-GLOBAL-2026-BASELINE) [Draft under review]. The Global Centre for Risk and Innovation (GCRI).

Every citation form of the whole report, BibTeX and RIS included, is on the edition home. Cite this report

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