Sustainability Atlas
Earth Systems & Climate Science·15 min read··...

Interview: the builder's playbook for Ocean circulation & heat uptake — hard-earned lessons

A practitioner conversation: what surprised them, what failed, and what they'd do differently. Focus on heat uptake, circulation shifts, and implications for extremes and sea level.

In 2025, the ocean absorbed 23 ± 8 zettajoules of heat—equivalent to 12 Hiroshima bombs detonating in the water every second. This marked the ninth consecutive year of record-breaking ocean heat content, with cumulative warming since 1960 reaching 452 ± 77 zettajoules. Yet despite 90% of Earth's excess heat being stored in the ocean, most climate risk frameworks barely scratch the surface of what this means for circulation patterns, sea level rise, and cascading impacts on regional weather extremes.

We spoke with oceanographers, climate modellers, and risk analysts across the UK, Europe, and North America to understand how practitioners are translating cutting-edge ocean science into actionable climate intelligence. What emerged was a picture of rapid scientific progress colliding with persistent gaps in monitoring infrastructure, model uncertainty, and the challenge of communicating non-linear tipping point risks to policymakers and corporate decision-makers.

Why It Matters

The ocean is the planet's primary climate regulator—absorbing heat, carbon dioxide, and redistributing thermal energy across hemispheres through circulation systems like the Atlantic Meridional Overturning Circulation (AMOC). For UK and European stakeholders, the stakes are particularly acute: the AMOC delivers warm water northward, moderating Western European winters and stabilising regional climate patterns that underpin agriculture, infrastructure planning, and energy demand forecasting.

In 2024, global mean sea surface temperature reached 0.61°C above the 1981–2010 baseline—0.07°C higher than 2023. The extraordinary SST spike between April 2023 and March 2024 was assessed as a 1-in-512-year event under current warming rates, essentially impossible without anthropogenic forcing. Marine heatwaves covered 91% of the ocean surface in 2023, with 2024 recording a record 100 marine heatwave days globally.

For policy and compliance professionals, these observations translate into material risk. The fourth global mass coral bleaching event (2023–2024)—the largest ever recorded—demonstrates ecosystem tipping points already being crossed. Climate-related disasters have cost the United States alone approximately $3 trillion since 1980, with ocean-driven extremes (hurricanes, coastal flooding, precipitation shifts) representing a growing share of that burden.

The convergence of accelerating ocean warming, potential AMOC weakening, and compound sea level rise creates what one climate risk analyst described as "the most consequential planning uncertainty of our generation."

Key Concepts

Ocean Heat Content as Climate's True Thermometer

Unlike surface air temperatures, which fluctuate with El Niño/La Niña cycles and short-term weather variability, ocean heat content (OHC) provides the most stable indicator of planetary energy imbalance. The upper 2000 metres gained 15–20 zettajoules annually over the past five years, regardless of surface temperature oscillations.

"We've been measuring the wrong thing for decades," explains a senior researcher at the Institute of Atmospheric Physics. "Surface temperature is the symptom. Ocean heat content is the disease progression. When you see OHC climbing relentlessly even during La Niña years—which should cool the planet surface—you understand the scale of committed warming already locked in."

The 2024 OHC increase of 16–18 zettajoules represented energy equivalent to 140 times global electricity generation. In 2025, the additional 23 zettajoules surpassed 200 times world electricity production—heat that will eventually resurface to warm the atmosphere.

The AMOC Tipping Point Debate

The Atlantic Meridional Overturning Circulation moves approximately 18 million cubic metres of water per second, transporting heat from the tropics to the North Atlantic. A 2024 landmark study by van Westen et al. demonstrated that the AMOC tipping point exists even in high-resolution, eddy-resolving ocean models—not just simplified simulations.

Research published in Science Advances developed a physics-based indicator suggesting the AMOC could begin collapsing as early as 2063 under high-emission scenarios (with a range of 2026–2095), though full shutdown would take over a century. However, a January 2025 Woods Hole Oceanographic Institution study found no AMOC decline over the past 60 years using air-sea heat flux data—directly contradicting SST-based reconstructions suggesting a 3 ± 1 Sverdrup decline since 1950.

"The scientific community agrees the tipping point exists," notes a Met Office oceanographer. "What we're still debating is whether we've already started sliding toward it, or whether we have more runway than proxy records suggest. That uncertainty is exactly what makes this so challenging for risk planning."

Compound Sea Level Dynamics

Global mean sea level reached its highest recorded level in 2024, with approximately 23 centimetres of rise since 1900. UK projections under medium emissions (SSP2-4.5) show 12–76 centimetres of additional rise by 2100, but the real concern is compound effects.

If the AMOC weakens significantly, dynamic sea level changes along the Atlantic coast of Ireland, the Netherlands, and Portugal would exceed the global average—adding regional amplification to thermal expansion and ice sheet contributions. Some UK coastlines could see up to 80 centimetres by 2100 when accounting for land subsidence. The frequency of 1-in-100-year flood events could increase by a factor of 10–100 around UK coasts.

What's Working

The Argo Revolution

The Argo programme—an international network of approximately 4,000 autonomous profiling floats—has transformed oceanography from a data-sparse to a data-rich science. By July 2024, Argo had collected over 3 million temperature and salinity profiles. The OneArgo expansion received $2.7 million in funding to integrate Core, Deep, and Biogeochemical Argo capabilities.

"Before Argo, we had shipping lane measurements and expensive research cruises," explains a NOAA programme manager. "Now we have continuous, global coverage to 2,000 metres—and Deep Argo floats reaching 6,000 metres. The improvement in ocean state estimation is transformational."

Deep Argo floats now operate to 3.7 miles depth, while Biogeochemical Argo tracks ocean acidification, oxygen levels, and carbon sequestration. Arctic expansion funding ($1.2 million in October 2024) addresses critical polar data gaps where ice previously blocked float operations.

Physics-Based Early Warning Systems

Utrecht University researchers developed what may become the gold standard for AMOC monitoring: a physics-based indicator derived from surface buoyancy fluxes over the North Atlantic. Analysis of 25 climate models provides probabilistic estimates of collapse onset timing.

Complementary research in November 2025 identified mid-depth warming (1,000–2,000 metres) in the equatorial Atlantic as a key fingerprint of AMOC slowdown. When circulation weakens, subsurface warming in the subpolar North Atlantic generates baroclinic Kelvin waves travelling southward—creating a detectable signal far from the high-latitude convection zones where direct measurement is most difficult.

"We now have multiple independent monitoring approaches," notes a PIK researcher. "The fingerprint redundancy is exactly what you want for tracking a system that might change faster than our observation networks can adapt."

Caltech CliMA's Constrained Projections

The Climate Modeling Alliance at Caltech developed a Bayesian framework using high-resolution (10km grid) ocean eddy modelling to constrain 21st-century AMOC projections. Their analysis predicts more limited weakening (approximately 4 Sverdrups) compared to unconstrained models projecting 8 Sverdrups of decline—reducing but not eliminating the uncertainty range that challenges policy planning.

What's Not Working

Model Divergence on Current State

The fundamental disagreement between SST-based reconstructions (suggesting 3 ± 1 Sverdrup AMOC decline since 1950) and heat flux analyses (showing no decline over 60 years) creates paralysis for risk managers.

"We have two credible research groups using different proxies and reaching opposite conclusions about whether the system is already weakening," observes a climate risk consultant. "For Scope 3 emissions planning or infrastructure investment decisions, that's an almost impossible epistemic situation. Which dataset do you believe?"

The RAPID mooring array at 26°N—the only continuous direct AMOC measurement—showed multi-Sverdrup decreases from 2004–2012, followed by recovery. The time series remains too short to distinguish trend from variability, and a single latitude cannot capture the full circulation system.

Southern Ocean Observation Gaps

The Southern Ocean—where upwelling processes may stabilise or destabilise the global overturning circulation—remains the most under-observed major ocean basin. A 2025 Nature study suggested Southern Ocean wind-driven upwelling could prevent AMOC collapse this century, but verification requires monitoring infrastructure that doesn't yet exist at scale.

Antarctic Bottom Water observations from NOAA's Atlantic Oceanographic and Meteorological Laboratory show a 12% decrease in northward transport between 2000 and 2020—a profound change in the deepest layer of global circulation. But spatial coverage remains sparse, and the drivers (ice sheet melt, wind pattern changes, or natural variability) are uncertain.

ENSO-AMOC Interaction Blind Spots

Climate models struggle to accurately simulate teleconnections between tropical Pacific variability (El Niño/La Niña) and North Atlantic circulation dynamics. The record SST spike of 2023–2024 coincided with unusual El Niño behaviour, but attribution remains contested.

"We know ENSO and AMOC interact through atmospheric bridges and ocean pathways," explains a UK Met Office modeller. "But our ability to simulate those interactions—let alone predict them on decadal timescales relevant for infrastructure planning—is limited. That's a fundamental capability gap."

Key Players

Established Leaders

Woods Hole Oceanographic Institution (WHOI) — The premier US oceanographic research centre, operating deep-water observation systems and leading AMOC research. Their January 2025 study challenging SST-based AMOC decline narratives reshaped the scientific debate.

Met Office Hadley Centre — The UK's authoritative source for climate projections, maintaining the HadGEM family of climate models and providing official sea level rise guidance for UK planning. Their January 2025 assessment concluded AMOC is unlikely to collapse this century but very likely to weaken.

Potsdam Institute for Climate Impact Research (PIK) — German research institute leading extended climate projections to 2300–2500. Their August 2024 CMIP6 analysis on potential AMOC shutdown after 2100 under high emissions established key scenario boundaries.

Institute of Atmospheric Physics (IAP/CAS) — Chinese Academy of Sciences institute coordinating international ocean heat content analysis. The 54-scientist, 7-country collaboration produces the definitive annual OHC assessments.

Emerging Startups

Aurelia (New Bedford, MA) — Developing lightweight autonomous ocean profilers for upper-ocean monitoring at lower cost than traditional Argo floats. Selected for the 2024 NOAA Ocean-Based Climate Resilience Accelerator.

Sofar Ocean — Operating the world's largest private ocean sensor network using low-cost Spotter buoys. Provides real-time wave, wind, and temperature data to maritime, offshore energy, and climate research clients.

Saildrone — Uncrewed surface vehicles conducting ocean data collection missions including hurricane tracking, Arctic surveys, and carbon flux measurement. Completed circumnavigation of Antarctica in 2022.

Vycarb — Autonomous ocean carbon measurement and removal systems. DOE Carbon Removal Purchase Pilot Prize semifinalist with East River pilot project for direct ocean capture verification.

Key Investors & Funders

National Science Foundation (NSF) — $23.5 million to University of Washington for Argo float construction; $2.7 million for OneArgo integration. Primary funder of US ocean observation infrastructure.

NOAA Climate Program Office — Operates Climate Observations and Monitoring and Climate Variability and Predictability programmes. $60 million allocated to Ocean-Based Climate Resilience Accelerators.

European Union Horizon Europe — Funding Atlantic observation networks and AMOC research through €95 billion framework programme. Supports Copernicus Marine Service providing operational oceanography.

Breakthrough Energy Ventures — Bill Gates-backed climate technology investor with ocean-climate portfolio including carbon removal and monitoring technologies.

Action Checklist

  1. Integrate ocean heat content into climate risk assessments: OHC provides more stable trend signals than surface temperature. Request ocean-based metrics from climate data providers and incorporate into scenario planning.

  2. Map AMOC sensitivity in regional planning: For UK and European coastal assets, model compound scenarios combining baseline sea level rise with dynamic adjustments from potential AMOC weakening. Add 20–30% contingency to Atlantic-facing infrastructure.

  3. Monitor the monitoring: Track developments in AMOC early warning indicators. Key publications from Utrecht University, PIK, and Met Office provide leading-edge assessments. Set alerts for new Advances in Atmospheric Sciences and Geophysical Research Letters ocean papers.

  4. Stress-test supply chains for marine heatwave impacts: With 91% of ocean experiencing heatwaves in 2023 and 100 marine heatwave days in 2024, evaluate fisheries, aquaculture, and shipping route dependencies. Coral-dependent tourism and coastal ecosystems face acute near-term risk.

  5. Engage with Argo data products: Open-access data from Global Data Assembly Centers enables independent verification of ocean conditions relevant to your geographic exposure. Build internal capacity to interpret OHC and temperature anomaly datasets.

  6. Request multi-century sea level projections: Standard 2100 timeframes miss committed warming effects. For long-lived infrastructure, require projections to 2150 or 2300 using frameworks like the Palmer et al. UK storylines approach.

  7. Participate in TCFD/ISSB ocean disclosure development: Current climate disclosure frameworks underweight ocean system risks. Contribute to standard-setting processes to ensure material ocean circulation risks receive appropriate attention.

  8. Fund observation gap closure: Consider corporate or philanthropic investment in Southern Ocean and Arctic monitoring expansion. The $25,000–$185,000 cost per Argo float represents high-leverage science infrastructure investment.

FAQ

Q: How confident are scientists that the AMOC will collapse, and when might it happen?

A: The scientific consensus is that an AMOC tipping point exists and could trigger irreversible weakening, but timing estimates span decades to centuries. Research published in 2024–2025 suggests collapse onset could occur as early as 2063 under high-emission scenarios (SSP5-8.5), with a range of 2026–2095. However, a January 2025 Met Office assessment concluded AMOC is "unlikely to collapse this century" while remaining "very likely to weaken." The key uncertainty is whether current observations show the system already declining (as SST-based proxies suggest) or remaining stable (as heat flux analyses indicate). For risk planning, prudent practice assumes weakening is probable and prepares for low-probability, high-impact collapse scenarios through stress testing rather than single-point predictions.

Q: What would AMOC collapse mean for UK and European climate?

A: Modelling studies project extreme winter cooling if AMOC collapses, with temperatures in parts of the UK and Netherlands potentially dropping to -20°C or lower. London could experience average winter cooling of 10°C, Bergen 15°C. Some models show 10–30°C winter temperature drops. However, summers would remain warmer than pre-industrial levels due to greenhouse gas forcing—creating a scenario described as "ice age winters, frying pan summers." Beyond temperature, impacts include more violent winter storms, regional sea level rise above global average along Atlantic coasts, reduced European precipitation, and strengthened jet stream effects over Northwestern Europe. Agricultural systems, energy demand, and infrastructure designed for current climate envelopes would face severe disruption.

Q: How does ocean heat uptake relate to ENSO cycles and extreme weather?

A: The ocean absorbs approximately 90% of excess heat from global warming, with ENSO cycles (El Niño and La Niña) modulating how that heat is distributed and released. El Niño events transfer heat from ocean to atmosphere, temporarily warming global surface temperatures, while La Niña suppresses surface warming by storing heat in the ocean interior. Critically, ocean heat content has increased by 15–20 zettajoules annually regardless of ENSO phase—demonstrating that the underlying warming trend continues independent of natural variability. For extreme weather, ocean heat content directly fuels hurricane intensification, marine heatwaves, and atmospheric moisture content driving extreme precipitation. The 2023–2024 SST spike—assessed as a 1-in-512-year event—coincided with unusual El Niño behaviour, and at least 104 countries recorded their hottest temperatures on record in the subsequent 12 months.

Q: What are the most reliable indicators for tracking ocean circulation changes?

A: Multiple complementary indicators provide the most robust monitoring approach. The RAPID array at 26°N offers direct AMOC measurement but only at one latitude. Physics-based indicators from surface buoyancy fluxes over the North Atlantic (developed by Utrecht University) provide early warning signals analysable across model ensembles. A newly identified "fingerprint"—mid-depth warming at 1,000–2,000 metres in the equatorial Atlantic—offers a real-time detection method as baroclinic Kelvin waves propagate southward from weakening convection zones. Research in November 2025 identified southern Atlantic salinity data as providing better early warning signals than classical SST-based approaches, which can generate false alarms. For practitioners, tracking multiple independent indicators rather than relying on any single metric provides more robust situational awareness.

Q: How should organisations incorporate ocean circulation uncertainty into climate disclosures?

A: Current TCFD and ISSB frameworks inadequately address ocean system risks, creating both compliance gaps and material disclosure opportunities for forward-looking organisations. Best practice involves: (1) explicitly acknowledging AMOC and ocean heat uptake as physical risk factors in scenario analysis; (2) quantifying exposure of coastal assets to compound sea level rise including dynamic AMOC effects; (3) stress-testing supply chains for marine heatwave and fisheries disruption; (4) incorporating multi-century timeframes for long-lived infrastructure decisions; and (5) documenting monitoring approaches for emerging tipping point indicators. Organisations can differentiate by demonstrating sophisticated understanding of non-linear ocean risks rather than treating climate change as a linear temperature progression. Engagement with scientific institutions (Met Office, PIK, WHOI) provides access to cutting-edge assessment capabilities for enterprise risk management.

Sources

The intersection of accelerating ocean heat uptake, contested AMOC stability signals, and compound sea level dynamics represents the defining physical risk challenge for climate-exposed organisations. Practitioners who build capacity to interpret ocean observation data, engage with evolving scientific consensus, and stress-test against non-linear circulation scenarios will be better positioned than those treating climate change as a simple temperature trajectory. The hard-earned lesson from those working at the frontier: the ocean's memory is long, its changes are committed, and the time for building adaptive capacity is now.

Topics

oceancirculationsea levelriskScope 3ENSOclimate models

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