The world's oceans are faced with an unprecedented loss of species comparable to the great mass extinctions of prehistory, a major report suggests today. The seas are degenerating far faster than anyone has predicted, the report says, because of the cumulative impact of a number of severe individual stresses, ranging from climate warming and sea-water acidification, to widespread chemical pollution and gross overfishing.

The coming together of these factors is now threatening the marine environment with a catastrophe "unprecedented in human history", according to the report, from a panel of leading marine scientists brought together in Oxford earlier this year by the International Programme on the State of the Ocean (IPSO) and the International Union for the Conservation of Nature (IUCN).

The stark suggestion made by the panel is that the potential extinction of species, from large fish at one end of the scale to tiny corals at the other, is directly comparable to the five great mass extinctions in the geological record, during each of which much of the world's life died out. They range from the Ordovician-Silurian "event" of 450 million years ago, to the Cretaceous-Tertiary extinction of 65 million years ago, which is believed to have wiped out the dinosaurs. The worst of them, the event at the end of the Permian period, 251 million years ago, is thought to have eliminated 70 per cent of species on land and 96 per cent of all species in the sea.

The panel of 27 scientists, who considered the latest research from all areas of marine science, concluded that a "combination of stressors is creating the conditions associated with every previous major extinction of species in Earth's history". They also concluded:

* The speed and rate of degeneration of the oceans is far faster than anyone has predicted;

* Many of the negative impacts identified are greater than the worst predictions;

* The first steps to globally significant extinction may have already begun.

"The findings are shocking," said Dr Alex Rogers, professor of conservation biology at Oxford University and IPSO's scientific director. "As we considered the cumulative effect of what humankind does to the oceans, the implications became far worse than we had individually realised.

"This is a very serious situation demanding unequivocal action at every level. We are looking at consequences for humankind that will impact in our lifetime, and worse, in the lifetime of our children and generations beyond that." Reviewing recent research, the panel of experts "found firm evidence" that the effects of climate change, coupled with other human-induced impacts such as overfishing and nutrient run-off from farming, have already caused a dramatic decline in ocean health.

Not only are there severe declines in many fish species, to the point of commercial extinction in some cases, and an "unparalleled" rate of regional extinction of some habitat types, such as mangrove and seagrass meadows, but some whole marine ecosystems, such as coral reefs, may be gone within a generation.

The report says: "Increasing hypoxia [low oxygen levels] and anoxia [absence of oxygen, known as ocean dead zones], combined with warming of the ocean and acidification, are the three factors which have been present in every mass extinction event in Earth's history.

"There is strong scientific evidence that these three factors are combining in the ocean again, exacerbated by multiple severe stressors. The scientific panel concluded that a new extinction event was inevitable if the current trajectory of damage continues."

The panel pointed to a number of indicators showing how serious the situation is. It said, for example, that a single mass coral bleaching event in 1998 killed 16 per cent of all the world's coral reefs, and pointed out that overfishing has reduced some commercial fish stocks and populations of "bycatch" (unintentionally caught) species by more than 90 per cent.

It disclosed that new scientific research suggests that pollutants, including flame-retardant chemicals and synthetic musks found in detergents, are being traced in the polar seas, and that these chemicals can be absorbed by tiny plastic particles in the ocean which are in turn ingested by marine creatures such as bottom-feeding fish.

Plastic particles also assist the transport of algae from place to place, increasing the occurrence of toxic algal blooms – which are also caused by the influx of nutrient-rich pollution from agricultural land.

The experts agreed that when these and other threats are added together, the ocean and the ecosystems within it are unable to recover, being constantly bombarded with multiple attacks.

The report sets out a series of recommendations and calls on states, regional bodies and the United Nations to enact measures that would better conserve ocean ecosystems, and in particular demands the urgent adoption of better governance of the largely unprotected high seas.

"The world's leading experts on oceans are surprised by the rate and magnitude of changes we are seeing," said Dan Laffoley, the IUCN's senior adviser on marine science and conservation. "The challenges for the future of the ocean are vast, but, unlike previous generations, we know now what needs to happen. The time to protect the blue heart of our planet is now, today and urgent."

The report's conclusions will be presented at the UN in New York this week, when delegates begin discussions on reforming governance of the oceans.

The five great extinctions

The Cretaceous–Tertiary extinction (the End Cretaceous or K-T extinction) 65.5 Mya (million years ago)

Plankton, which lies at the bottom of the ocean food chain took a hard hit in an event that also saw the demise of the last of the non-avian dinosaurs. The giant mosasaurs and plesiosaurs also vacated the seas. An asteroid or volcano eruptions are thought to be to blame.

The Triassic–Jurassic extinction (End Triassic) – 205 Mya

Having a profound affect on sea and land, this period saw 20 per cent of all marine families disappear. In total, half the species known to be living on Earth at that time went extinct. Gradual climate change, fluctuating sea-levels and volcanic eruptions are among the reasons cited for the disappearing species.

The Permian–Triassic extinction (End Permian) 251 Mya

A period known as the "great dying" was the most severe of the earth's extinction events, when 96 per cent of marine species were lost, as well as almost three-quarters of terrestrial species. The planet took a long time to recover from what has also been called "the mother of all mass extinctions".

The late Devonian extinction 360–375 Mya

Three-quarters of all species on Earth died out in a period that may have spanned several million years. The shallow seas were the worst affected and reefs would not recover for another 100 million years. Changes in sea level and climate change were among the suspected causes.

The Ordovician–Silurian extinction (End Ordovician or O-S) – 440–450 Mya

The third largest extinction in Earth's history had two peak dying times. During the Ordovician, most life was in the sea, so it was sea creatures such as trilobites, brachiopods and graptolites that were drastically reduced. In all, some 85 per cent of sea species were wiped out.

Waves of destruction

Case Study One in the panel's report assesses the "deadly trio" of factors – global warming, ocean acidification and anoxia (absence of oxygen). Most if not all of the five global mass extinctions in prehistory carry the fingerprints of these "carbon perturbations", the report says, and the "deadly trio" are present in the ocean today.

Case Study Two looks at coral reefs, and the fact that these "rainforests of the sea" (so-called for their species richness) are now facing multiple threats. The panel concluded that these threats acting together (pollution, acidification, warming, overfishing) will have a greater impact than if they were occurring on their own, and so estimates of how coral reefs will respond to global warming will have to be revised.

Case Study Three examines pollution, which is an old problem, but may be presenting new threats, as a wide range of novel chemicals is now being found in marine ecosystems, from pharmaceuticals to flame retardants, and some are known to be endocrine disrupters or can damage immune systems. Marine litter, especially, plastics, is a huge concern.