Increasingly, the world’s oceans are telling us our climate system may be changing faster and more dramatically than expected.

These new insights are made using a vast global network of instruments – from drifting floats and moored buoys to research vessels and underwater gliders – that quietly and continuously feed data to scientists.

Known as the Global Ocean Observing System (GOOS), it provides the fine-grained data that scientists need to detect changes, test climate models and refine projections of future risk.

But now there is rising concern this system itself is at risk – just when the world needs it most.

The hidden system behind modern forecasting

The GOOS is often described as a form of climate monitoring – but it is much more than that. It can best be understood as a network of complementary observing systems, each designed to capture different parts of the ocean in different ways.

Some 4000 autonomous Argo robotic floats sink every ten days down to 2000m depth, before rising to the surface to transmit temperature and salinity profiles to ground stations via satellite.

Underwater gliders target eddies, coastal currents and continental margins where floats cannot go. Elephant seals fitted with sensors collect data beneath polar sea ice in regions no other instrument can easily reach.

Each of these platforms answer questions the others cannot. And ocean observations collected by them now underpin many of the forecasting systems that modern societies rely on every day.

That includes the numerical weather models used to generate daily forecasts, which continuously ingest ocean data to predict evolving weather conditions, as well as newer artificial intelligence-based forecasting systems.

The same is true for hurricane and cyclone forecasts, as well as seasonal forecasting used to anticipate drought, harvests and energy demand. Marine heatwave warnings, sea-level projections and efforts to understand major current systems also rely on sustained long-term observations beneath the ocean surface.

These observations are key for monitoring El Niño climate patterns – including a major event already underway and likely to peak late this year – and major current systems such as the Atlantic Meridional Overturning Circulation.

While satellites can measure surface conditions, they still cannot directly observe the deeper waters where heat accumulates, currents reorganise and the precursors of future weather are already forming.

In short, the GOOS underpins everything from tomorrow’s storm warnings to next century’s climate adaptation plans.

Yet our newly published analysis suggests the system delivering those observations is far more fragile than most people realise.

We found that if observations from a single major contributor, the United States, were withdrawn from GOOS, errors in estimates of how fast the ocean is warming would jump by 163% – worse than randomly losing 80% of all global ocean data.

The reason is largely geographical: US instruments cover every ocean basin and fill critical gaps no other nation currently monitors.

And this is no theoretical concern. Proposed cuts to the National Oceanic and Atmospheric Administration (NOAA) and the National Science Foundation in the United States now threaten exactly this contribution.

Elsewhere, observing systems are also under growing strain, with European programmes facing mounting funding pressure.

In China, scientists and policymakers are trying to build a more resilient national observing effort – but without the resources currently required to fully support it.

A resource the world can’t afford to lose

The total annual cost of operating the GOOS – across all platforms and personnel worldwide – is on the order of US$1.1 billion (about NZ$1.8 billion).

If that sounds expensive, consider that a single major hurricane season can cost the United States hundreds of billions of dollars, while marine heatwaves have already collapsed fisheries and triggered mass coral bleaching around the world.

Compared with the economic damage linked to ocean-driven extreme weather and climate disruption, ocean observation is one of the highest-return public investments available.

The international scientific conference OceanObs'29, to be held in China in three years’ time, will be an opportunity to negotiate a more balanced global observing system – one better aligned with today’s economic realities and maritime interests.

It should also encourage greater scientific cooperation among countries, helping ensure complementary observing networks collectively cover as much of the global ocean as possible.

Maintaining that coverage requires constant renewal.

Argo floats typically last four to five years before their batteries fail. This means they must continually be deployed to prevent gaps emerging across the oceans.

New Zealand plays a surprisingly important role here. Since 2004, the research vessel Kaharoa has helped deploy more than 1,100 Argo floats for international partners across the Pacific and Southern Ocean.

This demonstrates that even smaller countries can use their institutions, expertise and maritime interest to make important contributions.

At the same time, if any one component of the GOOS is removed because of political decisions made in the US or elsewhere, the whole system’s ability to deliver reliable information would degrade.

That would require a rebuild of the system which would prove much more difficult and expensive than the cost of sustaining it today.

More importantly, it could leave the world flying blind into the most consequential transformation of the planet’s climate in human history.

The author acknowledges the contributions of Sabrina Speich, John P. Abraham and Lijing Cheng to this article.

Kevin Trenberth does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.

The world relies on a modest number of countries to keep watch over the ocean. That arrangement is starting to fail. Europe and Asia must now decide whether to let the system unravel, or to take it up together.

Right now, in every ocean basin on Earth, a global network of instruments measures the state of the sea.

Research ships steam along oceanographic transects from surface to seafloor. Anchored buoys watch the tropical oceans for the first signs of El Niño or tropical cyclones and take the pulse of the thermohaline circulation. Some four thousand autonomous floats sink every ten days to two thousand metres before rising to transmit temperature and salinity to ground stations via satellite. Underwater gliders patrol continental margins, and drifting buoys ride the surface in the most remote waters. Hundreds of elephant seals carry miniaturised sensors beneath the polar sea ice…

Together, this network produces invaluable information that allows societies to anticipate and respond to a changing ocean and weather conditions, and protect the ocean in return.

It is also far more fragile than most people, and most governments realise. A new study published in Nature Climate Change has measured for the first time just how fragile the ocean watch network is.

The result is alarming. If observations from a single major contributor, the United States, were withdrawn from the Global Ocean Observing System (GOOS), the errors in our estimate of how fast the ocean is warming would jump by 163 percent. That is worse than randomly losing 80 percent of all global ocean data. The reason is geographical: US instruments cover every ocean basin and plug critical gaps that no other nation currently fills.

This is not a theoretical concern. Proposed cuts to National Oceanic and Atmospheric Administration (NOAA) and the National Science Foundation in the United States now threaten exactly this contribution. And the situation is barely better on the other side of the Atlantic.

The pressures are not confined to one side of the Atlantic, nor to the West. In China, scientists and policymakers are working to build a more resilient national contribution to ocean observation, but without the resources the moment requires. The marine monitoring system the world relies on is under strain almost everywhere.

An observing system, not a programme

Public conversations about ocean observations often focus on Argo floats.

Each Argo is essentially a sealed cylinder of pressurised electronics with a clever buoyancy chamber: it floods with seawater to sink and is evacuated to rise again. These autonomous robots have transformed ocean science this century.

However, Argo is just one component of GOOS and the complementarity of its parts matters.

• Argo profiles the upper two kilometres of the open ocean.

• Research vessels go deeper: GO-SHIP cruises survey from surface to seafloor along long repeated transects, providing the high-precision reference measurements that calibrate every other instrument and help validate climate models.

• Moored buoys deliver continuous time series critical for monitoring El Niño, the Atlantic Meridional Overturning Circulation, and the conditions in which tropical cyclones form.

• Underwater gliders target coastal currents, eddies and continental margins that floats cannot resolve.

• Elephant seals carry sensors into under-ice regions of the polar oceans that no other instrument can reach.

Each platform answers questions the others cannot.

Remove any one of these ocean watch components, and the observing system’s ability to deliver reliable information degrades not in proportion to the volume of data lost, but in proportion to where the gaps appear.

What this network actually delivers

The Global Ocean Observing System is too often described as “climate monitoring,” but it does so much more.

Every operational weather forecast is built on these data. The numerical weather prediction systems run by the European Centre for Medium-Range Weather Forecasts, by Météo France, and by every other major weather service ingest ocean observations many times a day.

Without them, forecasts drift quickly out of skill.

The new artificial-intelligence-based forecast systems Pangu-Weather and GraphCast, despite their impressive performance, rely entirely on the same observational stream.

AI does not replace observations; it depends on them.

Sub-seasonal to seasonal forecasting, to help anticipate harvest seasons, energy demand and water availability weeks to months ahead, depends critically on knowledge about subsurface ocean heat and salinity.

Tropical cyclone track and intensity forecasts, central to early warning and evacuation decisions, depend on ocean heat content beneath the surface, not just sea surface temperature, because hurricanes draw their explosive energy from the warm layers down to at least 200m depth.

Marine heatwave warnings, now used routinely by fisheries managers worldwide, are impossible without sustained subsurface observation.

Sea-level projections used to design coastal infrastructure require decades of consistent measurements, and salinity adds the density information essential for determining all ocean currents, including the AMOC.

In short, GOOS underpins operational services from tomorrow’s storm warnings to next century’s adaptation plan. It is not a luxury but essential.

Why models and artificial intelligence alone cannot save us

There is a persistent misconception, amplified by the rise of AI, that sufficiently advanced models can substitute for direct observations. They cannot.

Every forecast model, whether traditional or AI- based, relies on data assimilation: a continuous nudged adjustment of the simulation toward real-world measurements. An AI model trained on a richly observed past will perform poorly in a sparsely observed present. In a world of rising extremes and shifting ocean states, historical patterns become less reliable.

An observation not made is lost forever. Satellite measurements of the sea surface cannot tell us what is happening hundreds or thousands of metres below, where heat accumulates, currents reorganise, and the precursors of the next season’s weather are already forming. To see beneath the surface, we need instruments in the water.

The cheapest insurance we have

The argument that ocean observation is too expensive collapses on contact with the numbers.

The total annual cost of the global system, across all platforms and personnel, runs on the order of one billion euros worldwide. The European share is a fraction of that.

Extreme weather events linked to ocean conditions caused tens of billions of euros in damage across Europe in 2024 alone.

A single major North Atlantic hurricane season can cost the United States hundreds of billions of dollars. Marine heatwaves have collapsed fisheries worth billions and triggered mass coral bleaching on every reef system on Earth. Failed seasonal forecasts cascade through agriculture, energy and humanitarian response, with consequences rarely tallied.

Every euro spent on ocean observation returns many times its value. It is one of the highest-return public investments available.

Europe’s choice

Europe needs to treat ocean observations as critical infrastructure, equivalent to satellite navigation or meteorological services. That means stable, multi-year funding for the operational backbone of the system: the floats, ships, moorings, gliders and data centres that process and deliver the data.

France has the second-largest Exclusive Economic Zone in the world but contributes around 5 percent of global ocean temperature profile data. Present in the Atlantic, Pacific and Indian Oceans, France has five departments and regions and seven overseas collectivities, which are home to 2.7 million French citizens.

Australia contributes more than three times as much.

The European Union contributes about 12 percent, less than a quarter of the American share. Europe, and France in particular, should substantially increase its contribution.

OceanObs’29, the decadal international conference set to be held this time in China, is an opportunity to negotiate a more balanced global system, reflecting economic capacity and maritime interests rather than historical accident.

Europe-China scientific cooperation should increase, as they have largely complementary observing footprints. Together, they would cover much of the global ocean.

The narrowing window

The danger is a gradual erosion of the information on which a growing share of human activity and the blue economy now depends.

Cyclone warnings become less reliable, seasonal forecasts less skilful, sea-level projections less precise. Each loss maybe individually tolerable. Together, they amount to flying blind into the most consequential transformation of the planet’s climate in human history.

The ocean observing system is a planetary public service, built over decades by many nations. France and Europe possess the institutions, expertise and the maritime interest to play a far larger role.

What is missing is the political decision to act, while the system can still be sustained. The loss of collaboration among nations would force a rebuild far more difficult and expensive than sustained investment in what already works.

The window remains open but is narrower than it was.

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Sabrina Speich a reçu des financements de l'ERC, EU Horizon 2030, CNES TOSCA et ANR. Sabrina Speich est présidente du comité d'experts du "Ocean Observations for Physics and Climate" des programmes UN GOOS et GCOS.

John Abraham, Kevin Trenberth et Lijing Cheng, ne travaillent pas, ne conseillent pas, ne possèdent pas de parts, ne reçoivent pas de fonds d'une organisation qui pourrait tirer profit de cet article, et n'ont déclaré aucune autre affiliation que leur poste universitaire.