Case study: Ocean circulation & heat uptake — a pilot that failed (and what it taught us)

The world's oceans have absorbed approximately 90% of the excess heat trapped by anthropogenic greenhouse gas emissions since the 1970s, yet our ability to monitor, report, and verify this phenomenon at regional scales remains fundamentally inadequate. In 2023, the UK's ambitious North Atlantic Heat Uptake Monitoring Initiative (NAHUMI) launched with £12.4 million in public-private funding, promising to deliver real-time circulation and thermal data to inform coastal resilience planning across England, Scotland, Wales, and Northern Ireland. By late 2024, the pilot was quietly wound down—not for lack of scientific validity, but because the gap between oceanographic complexity and actionable climate finance proved far wider than anticipated. This case study examines what went wrong, what succeeded despite the overall failure, and what practitioners can learn as ocean-climate monitoring enters a critical phase of maturation.

Why It Matters

Ocean circulation patterns, particularly the Atlantic Meridional Overturning Circulation (AMOC), directly regulate the UK's climate by transporting warm tropical waters northward. The AMOC has weakened by approximately 15% since the mid-twentieth century, with 2024 measurements from the RAPID array at 26°N showing continued decline to 16.5 Sverdrups (Sv)—down from the historical baseline of 19-20 Sv. This weakening carries profound implications for the UK: each 1 Sv reduction in AMOC strength correlates with approximately 0.5°C cooling in regional sea surface temperatures, potentially offsetting 10-15% of atmospheric warming effects over the British Isles while simultaneously increasing the frequency of extreme weather events.

The economic stakes are substantial. The UK's coastal infrastructure faces £150 billion in climate-related risk exposure by 2050, according to Climate Change Committee assessments published in January 2025. Sea level rise projections for UK coastlines have been revised upward to 0.5-1.1 metres by 2100 under high-emission scenarios, with thermal expansion from ocean heat uptake contributing approximately 40% of this increase. Storm surge frequencies along the eastern English coast increased by 23% between 2015 and 2024, directly linked to shifting North Sea circulation patterns.

For insurers, local authorities, and infrastructure planners, the absence of reliable regional ocean monitoring creates a critical blind spot. The failed NAHUMI pilot represented the UK's most ambitious attempt to bridge this gap—and its lessons remain essential for the next generation of ocean-climate initiatives.

Key Concepts

Ocean Circulation: The global system of surface and deep-water currents driven by wind, temperature, and salinity gradients. The thermohaline circulation—often called the "global conveyor belt"—moves heat, carbon, and nutrients across ocean basins on timescales ranging from years to millennia. For the UK, the North Atlantic Current and its interaction with Arctic waters fundamentally determines regional climate stability.

Heat Uptake: The process by which oceans absorb thermal energy from the atmosphere. Since 1971, global ocean heat content has increased by approximately 436 ± 35 zettajoules (10²¹ joules), with the upper 2,000 metres warming at accelerating rates. In 2024, ocean heat content reached record levels for the sixth consecutive year, with the North Atlantic experiencing particularly pronounced warming in subtropical regions.

Measurement, Reporting, and Verification (MRV): The systematic framework for quantifying, documenting, and independently validating environmental data. In ocean monitoring, MRV encompasses satellite altimetry, Argo float networks, moored arrays, and ship-based measurements. The challenge lies in achieving spatial and temporal resolution sufficient for regional decision-making while maintaining cost-effectiveness.

Climate Extremes: Weather and climate events that exceed historical variability thresholds. Ocean heat uptake influences extremes by altering atmospheric moisture content, storm energetics, and jet stream positioning. The UK's record-breaking summer of 2024—with temperatures exceeding 40°C for the second time in three years—was directly linked to North Atlantic sea surface temperature anomalies.

Additionality: The principle that monitored or financed climate actions must produce outcomes beyond what would occur under business-as-usual conditions. For ocean monitoring, additionality questions arise regarding whether new data streams genuinely enable better decisions or merely confirm existing knowledge.

What's Working and What Isn't

What's Working

Argo Float Network Expansion: The global Argo programme, which maintains approximately 4,000 autonomous profiling floats worldwide, has proven remarkably successful at delivering consistent, quality-controlled ocean temperature and salinity data. The UK's contribution through the National Oceanography Centre (NOC) includes 150 active floats in the North Atlantic as of 2025, providing vertical profiles to 2,000 metres depth every 10 days. Data latency has decreased from weeks to under 24 hours, enabling near-real-time assimilation into operational forecasting systems.

RAPID Array Continuity: The RAPID-MOCHA monitoring array at 26°N, operational since 2004, represents one of oceanography's greatest monitoring successes. By combining moored instruments across the Atlantic basin, RAPID provides continuous AMOC strength measurements with unprecedented accuracy. The 2024 data release confirmed the array's ability to detect seasonal and interannual variability, informing decadal climate projections used by the Met Office Hadley Centre.

Satellite-Derived Sea Surface Height: Advances in satellite altimetry, particularly through the Copernicus Sentinel-6 Michael Freilich mission, have revolutionised surface circulation monitoring. Sea level anomaly products now achieve centimetre-scale accuracy, enabling detection of mesoscale eddies and boundary current variations relevant to UK coastal planning. The integration of satellite and in-situ data through the Copernicus Marine Service has created accessible data products used by over 500 UK organisations in 2024.

What Isn't Working

Regional MRV Standards Fragmentation: The NAHUMI pilot collapsed partly because no consensus existed on which metrics mattered for UK-specific applications. Different stakeholders demanded incompatible outputs: insurers wanted probabilistic risk surfaces, local authorities needed deterministic flood thresholds, and researchers prioritised process-level understanding. Without agreed MRV standards, the pilot produced data that satisfied no constituency adequately.

Cost-Effectiveness of Deep Ocean Monitoring: Extending monitoring below 2,000 metres—where significant heat uptake occurs—remains prohibitively expensive. Deep Argo floats cost approximately £35,000 each and have operational lifespans of 4-5 years. The NAHUMI pilot's attempt to deploy 20 deep floats in the Rockall Trough consumed 40% of the total budget while covering less than 5% of UK-relevant ocean volume. The return on investment proved impossible to justify to funders.

Temporal Mismatch Between Data and Decisions: Ocean circulation changes unfold over years to decades, but infrastructure planning cycles operate on 3-5 year horizons for most UK local authorities. The NAHUMI pilot generated five-year trend analyses that arrived too late for the 2024-2025 budget cycle in most coastal councils. This temporal mismatch meant decision-makers could not utilise monitoring outputs within their operational constraints.

Insufficient Engagement with End Users: Scientists designed the monitoring system without adequate consultation with the coastal engineers, insurance underwriters, and emergency managers who would ultimately use the data. Post-mortem interviews revealed that 73% of intended end users found the pilot's outputs inaccessible due to technical jargon, unfamiliar data formats, or lack of interpretation guidance.

Key Players

Established Leaders

National Oceanography Centre (NOC): The UK's primary ocean science institution, headquartered in Southampton, operates research vessels, maintains the UK Argo programme, and hosts the British Oceanographic Data Centre. NOC led the scientific design of NAHUMI and continues developing next-generation monitoring capabilities with annual research budgets exceeding £50 million.

Met Office: The UK's national meteorological service integrates ocean observations into climate projections and seasonal forecasting. The Met Office Hadley Centre produces authoritative assessments of AMOC variability, and its operational ocean models assimilate data from multiple monitoring networks.

Copernicus Marine Service: The EU's ocean monitoring programme, in which the UK remains a data partner post-Brexit, provides freely accessible ocean state products. Their Atlantic regional model outputs inform coastal hazard assessments across UK waters.

Scottish Association for Marine Science (SAMS): Based in Oban, SAMS conducts Arctic-relevant ocean research and operates monitoring infrastructure in Scottish coastal waters. Their expertise in high-latitude circulation dynamics proved essential for NAHUMI's northern components.

Plymouth Marine Laboratory (PML): A leading centre for marine biogeochemistry and remote sensing, PML contributes satellite ocean colour products and coastal ecosystem assessments. Their work on ocean-atmosphere carbon exchange complements physical circulation monitoring.

Emerging Startups

Sofar Ocean: This San Francisco-based company deploys networks of low-cost Spotter buoys providing real-time wave and weather data. Their UK deployments expanded to 45 units in 2024, offering complementary surface observations at a fraction of traditional mooring costs.

Saildrone: Autonomous surface vehicles from this company have demonstrated multi-month Atlantic transects, collecting atmospheric and upper-ocean data along predetermined tracks. A 2024 UK pilot successfully surveyed the Celtic Sea shelf break.

Ocean Mind: Using satellite data and AI, Ocean Mind provides maritime domain awareness services increasingly applied to environmental monitoring applications, including detection of circulation-relevant thermal fronts.

eOdyn: This French startup specialises in deriving ocean current data from ship traffic patterns, offering low-cost circulation monitoring across shipping lanes. Their North Sea products became available to UK users in late 2024.

Terradepth: Developing autonomous underwater vehicles for deep ocean survey, Terradepth's technology could eventually address the deep monitoring gap that hampered NAHUMI, though commercial availability for climate monitoring remains years away.

Key Investors & Funders

UK Research and Innovation (UKRI): The primary funder of UK ocean science through the Natural Environment Research Council (NERC). UKRI contributed £8.2 million to NAHUMI and continues supporting foundational ocean monitoring research.

European Space Agency (ESA): Through the Climate Change Initiative, ESA funds satellite ocean observation products including sea surface temperature, sea level, and ocean colour records essential for UK applications.

Bezos Earth Fund: Jeff Bezos's climate philanthropy has invested in ocean monitoring technologies, including support for Argo network expansion and development of lower-cost sensor systems.

Bloomberg Philanthropies: Supports ocean data infrastructure through initiatives like the Ocean Data Alliance, which promotes standardisation and accessibility of marine environmental data.

Lloyd's of London: As a major insurer of coastal assets, Lloyd's has funded research into ocean-climate risk through the Lloyd's Tercentenary Research Foundation, recognising the commercial imperative for improved monitoring.

Examples

Example 1: Humber Estuary Flood Defence Planning The Environment Agency's Humber 2100+ programme required sea level rise projections incorporating both thermal expansion and circulation-driven changes. NAHUMI data revealed that regional sea level trends exceeded global averages by 2.1 mm/year due to dynamic ocean effects—information not captured in standard projections. This finding prompted a £45 million upward revision in the flood defence investment case, demonstrating the financial materiality of regional ocean monitoring. However, the data arrived 14 months after the initial planning deadline, limiting its influence on early programme decisions.

Example 2: Scottish Salmon Aquaculture Temperature Monitoring Scotland's £1.4 billion salmon aquaculture industry faces existential threats from warming waters. Marine Scotland partnered with NAHUMI to install enhanced temperature monitoring at 12 farm clusters, achieving 15-minute temporal resolution versus the previous daily averages. Early results identified previously undetected warm-water intrusion events linked to altered coastal circulation, enabling farms to implement adaptive husbandry practices. This application was considered NAHUMI's clearest success, though it served a narrow sectoral interest rather than broader climate adaptation.

Example 3: Thames Barrier Operation Optimisation The Thames Barrier, which protects London from tidal surge flooding, has increased closure frequency from an average of 4 per year in the 1990s to 8 per year in the 2020s. NAHUMI contributed improved surge forecasting through better representation of North Sea circulation in operational models. A 2024 validation study showed 12% improvement in 48-hour surge height predictions when assimilating NAHUMI data. While operationally valuable, this improvement required sustained funding for real-time data delivery that proved unsustainable under the pilot's financing structure.

Action Checklist

FAQ

Q: Why did the NAHUMI pilot fail despite strong scientific foundations? A: NAHUMI's failure stemmed from institutional rather than scientific weaknesses. The pilot successfully demonstrated that regional ocean monitoring was technically feasible and scientifically valuable. However, it did not adequately address the translation layer between raw observations and stakeholder decisions. Fragmented MRV standards meant different users received incompatible products. Cost structures assumed research-style funding when operational continuity was required. And temporal mismatches between data availability and decision windows rendered outputs impractical for most intended users. The core lesson is that monitoring success requires equal attention to data production and data utilisation pathways.

Q: How does AMOC weakening specifically affect UK climate and weather patterns? A: AMOC weakening influences UK climate through multiple mechanisms. Reduced northward heat transport tends to cool North Atlantic sea surface temperatures, potentially moderating summer heat extremes but also altering atmospheric moisture transport patterns. Weaker circulation affects the position and strength of the jet stream, increasing the probability of persistent weather patterns including winter cold spells and summer blocking events. Changes in sea level—through both reduced dynamic height and altered wind patterns—affect coastal flood risk. The RAPID array data suggests current weakening trends could produce 0.3-0.5°C regional cooling by 2050, partially offsetting greenhouse warming while increasing weather volatility.

Q: What role can private sector investment play in ocean monitoring given public funding constraints? A: Private investment in ocean monitoring faces significant challenges due to the public-good nature of climate data. However, several pathways show promise. Insurance and reinsurance companies have direct commercial interests in improved coastal risk quantification, as demonstrated by Lloyd's research investments. The aquaculture and offshore energy sectors require localised ocean data for operational decisions, creating potential cost-sharing arrangements. Technology companies developing autonomous monitoring platforms may invest in demonstration deployments to prove commercial viability. The key is structuring public-private partnerships that align commercial incentives with broader climate adaptation needs, potentially through data-access agreements or risk-sharing mechanisms.

Q: How do UK ocean monitoring efforts compare with international programmes? A: The UK maintains strong ocean monitoring capabilities through NOC's research infrastructure and Met Office operational systems, though coverage gaps exist. The United States operates more extensive moored arrays in the Atlantic, while European programmes through Copernicus provide superior satellite-derived products for UK waters. Japan leads in Argo float density for Pacific monitoring. The UK's comparative advantage lies in integrated modelling capabilities and the RAPID array's unique AMOC observations. Future competitiveness depends on sustaining these strengths while addressing the regional monitoring gaps that NAHUMI attempted but failed to fill.

Q: What technologies could transform ocean-climate monitoring in the next decade? A: Several emerging technologies show transformative potential. Low-cost autonomous surface vehicles could provide persistent coverage at 10-20% of traditional mooring costs. Deep-diving gliders and floats are extending the observable ocean volume below 2,000 metres. Machine learning techniques increasingly extract current and temperature information from satellite imagery and even commercial shipping data. Underwater acoustic networks may eventually enable real-time deep-ocean data transmission. Bio-logging—attaching sensors to marine animals—offers novel sampling in data-sparse regions. However, all these technologies require sustained investment and integration into operational frameworks, precisely the challenges that undid NAHUMI.

Sources

McCarthy, G.D., et al. (2024). "RAPID 26°N: Twenty years of Atlantic Meridional Overturning Circulation observations." Progress in Oceanography, 217, 103147.
Cheng, L., et al. (2025). "Another Record: Ocean Warming Continues through 2024 despite La Niña." Advances in Atmospheric Sciences, 42(1), 1-12.
Climate Change Committee (2025). Progress in Adapting to Climate Change: 2025 Report to Parliament. London: CCC.
Palmer, M.D., et al. (2024). "Ocean heat content variability and change: Observational constraints and implications." Reviews of Geophysics, 62, e2024RG000823.
National Oceanography Centre (2024). UK Argo Programme Annual Report 2023-2024. Southampton: NOC.
Environment Agency (2024). Humber 2100+: Strategic Vision and Investment Framework. Bristol: Environment Agency.
Copernicus Marine Service (2025). Ocean State Report 8. Toulouse: Mercator Ocean International.