The Ocean, Assessed

A few weeks ago, the United Nations published the Third World Ocean Assessment. Put together by around 600 experts from 86 countries, and covering everything from coral reefs and fisheries to ocean governance, human health, pollution, and the rights of coastal communities, it is an absolute beast of a document.

So today, I’m going to pull out some of the highlights.

First things first, what is the World Ocean Assessment anyway?

Every five or so years, the United Nations convenes scientists from around the world to produce a comprehensive assessment of the state of the global ocean. The Third World Ocean Assessment (WOA III) covers what happened in the ocean between 2018 and 2023, and compares it to the previous assessment. The assessments aren't creating new research. They synthesise thousands of existing studies to give us an overall picture of what we know, what's changed, and what we're still uncertain about. If you're familiar with the Intergovernmental Panel on Climate Change (IPCC) reports, they're a bit like that, but specifically about the ocean.

So what are some of the highlights?

The TL;DR version is that generally the ocean isn't in tip-top condition, and that is impacting us in many different ways - health, jobs, culture.... we have lots to do, but we are making some progress.

What's not going well

The ocean is warming faster than we thought

Around 16% of all the heat the ocean has absorbed since 1955 has been absorbed since 2018 alone. Sea levels are rising at ever faster rates, and the Arctic could be ice-free in September within decades.

Coral reefs are in serious trouble

The report suggests that 90% of coral reefs could disappear if warming exceeds and stays above 1.5°C above pre-industrial levels (for context, 2023, 2024, and 2025 global temperatures all exceeded this threshold). The Caribbean has already lost 80% of its coral cover since the 1970s. Marine heat waves - heat waves in the ocean - are leaving less and less time for reefs to recover.

Plastic is everywhere

Plastic is now found throughout the ocean, from coastlines to the deep sea. The report estimates that tens of millions of tonnes of plastic waste enter the ocean each year. These plastics can cause harm to animals (including us) who consume the plastics without realising, create chemical contaminants, and more.

Fisheries are still declining

The proportion of global fish stocks within biologically sustainable levels has fallen to 62.3%, down from 64.6% in 2019. Illegal, unreported and unregulated fishing accounts for an estimated 8 to 14 million metric tons of catch every year. Yep, that's a lot of fish nobody's officially counting and thus managing.

Meanwhile, small-scale fisheries employ some 60 million people worldwide, but many of those communities remain marginalised and lack secure access to the resources they depend on.

Coastlines are under pressure

Human infrastructure already affects 33% of global beaches, and up to 26% are at risk of severe sand loss by the end of the century. Coastal habitats like mangroves, seagrasses, and salt marshes are declining worldwide due to development, pollution, and climate change. The people most affected are often those who depend on them most: coastal and Indigenous communities who frequently lack secure access to resources and meaningful participation in the decisions that affect them.

We're losing the people who can tell us what lives in the ocean

The number of taxonomists, people who identify and classify species, is declining globally (not just in the marine space might I add). Even with newer technologies such as genetic sequencing and environmental DNA (eDNA), taxonomists are crucial for identifying species and more.

Human health risks are increasing

The report also flags growing risks to human health from chemical contaminants, pathogens, harmful algal blooms, microplastics, and marine debris. Climate change can make some of these risks worse, including through warming seas, extreme events, and shifting disease vectors.

Governance is improving but still fragmented

There are now 57 global treaties relating to ocean protection, but they don't necessarily integrate well with each other. Fragmentation across sectors and regions is one of the biggest barriers to effective ocean management.

Reasons for hope

There are now 57 global treaties relating to ocean protection

Yes, I know I just mentioned that in the "what's not going well section," but the fact that we now have 57 global treaties tells us that important "high-level" conversations are happening more and more.

Two of the big treaty bright spots are the High Seas Treaty and the Fisheries Subsidies Agreement. The High Seas Treaty creates a framework for protecting marine biodiversity in what's officially known as areas beyond national jurisdiction. The Fisheries Subsidies Agreement aims to tackle the billions in government subsidies that prop up unsustainable fishing. I wrote more about what the High Seas Treaty does, and why it matters, here.

Some species and habitats that were in decline are doing better

Mangrove loss has slowed significantly thanks to conservation efforts. Some fish populations, including certain tuna species, are showing signs of recovery. Ok, it's not everything and I daresay there are more declines than signs of hope, but these improvements do show that we can make a difference if we want to.

We're discussing human rights more

Since the last assessment, human rights have become much more prominent in ocean governance discussions. Those human rights concerns include who gets access, who gets support, whose voice is heard, and who gets decision-making power and economic opportunities.

Local, Indigenous, and traditional owner knowledge is being recognised

Science provides us with huge amounts of rigorous, verifiable knowledge and data that can help us make good decisions, but it's not the only knowledge system that can help us understand the ocean and act more sustainably. We're seeing local, indigenous, and traditional owner knowledge increasingly entering into ocean governance conversations.

Ocean observations are giving us crucial information

The tools we use to watch the ocean like autonomous floats, underwater drones, satellite sensors, and environmental DNA, have expanded enormously in recent years. Despite gaps in what we observe and where, we're generating data at scales that simply weren't possible a decade ago and that's helping us understand more about the ocean and even predict what might happen next.

What we still don't know

Most of the seafloor is unmapped

As of 2025, only 27.3% of the seafloor had been mapped. Or more precisely, mapped with sufficient detail that we can actually make meaningful, evidence-based decisions on things like trawling or building infrastructure or what types of protections we need to put where.

Nanoplastics are still a mystery

We know that there is a lot of plastic in the ocean, but we're still piecing together just how much. Nanoplastics - tiny plastic particles so small they're invisible to the naked eye - are a particular mystery. How much is there? Where are they? How much is getting into our bodies and the bodies of marine creatures?

We don't fully understand the cumulative effects

We're getting better at understanding how individual pressures are impacting the ocean and us, and, in some cases, at measuring them. But nothing happens in isolation, and pressures can interact and accumulate. We clearly need more research in this area.

But wait, there's more

There is, of course, far more in the report than I can cover in a single Brief. Over the next few issues, I’ll be coming back to explore some of these and other topics in more detail.

For now, I'll leave you with this from António Guterres, UN Secretary-General.

"We cannot keep treating the ocean as limitless. We must build a new relationship with the ocean: Grounded in science. Framed by international law. And built on shared responsibility – across nations, sectors, and generations – to advance the Sustainable Development Goals.”