Life in the world’s oceans faces far  greater change and risk of large-scale extinctions than at any previous time in  human history, a team of the world’s leading marine scientists has warned.

The researchers from Australia, the US,  Canada, Germany, Panama, Norway and the UK have compared events which drove  massive extinctions of sea life in the past with what is observed to be taking  place in the seas and oceans globally today.

Three of the five largest extinctions  of the past 500 million years were associated with global warming and  acidification of the oceans – trends which also apply today, the scientists say  in a new article in the journal Trends in  Ecology and Evolution.

Other extinctions were driven by loss  of oxygen from seawaters, pollution, habitat loss and pressure from human  hunting and fishing – or a combination of these factors.

“Currently,  the Earth is again in a period of increased extinctions and extinction risks,  this time mainly caused by human factors,” the scientists stated. While the  data is harder to collect at sea than on land, the evidence points strongly to  similar pressures now being felt by sea life as for land animals and plants.

The researchers conducted an extensive  search of the historical and fossil records to establish the main causes of  previous marine extinctions – and the risk of their recurring today.

“We  wanted to understand what had driven past extinctions of sea life and see how  much of those conditions prevailed today,” says co-author Professor John  Pandolfi, of the ARC Centre of  Excellence for Coral Reef Studies and The University of Queensland, an  authority on the fate of coral reefs in previous mass extinction events.

“It is very useful to look back in time  – because if you forget your history, you’re liable to repeat it.”

Marine extinction events vary greatly.  In the ‘Great Death’ of the Permian 250 million years ago, for example, an  estimated 95 per cent of marine species died out due to a combination of  warming, acidification, loss of oxygen and habitat. Scientists have traced the  tragedy in the chemistry of ocean sediments laid down at the time, and abrupt  loss of many sea animals from the fossil record.

“We are seeing the signature of all  those drivers today – plus the added drivers of human overexploitation and  pollution from chemicals, plastics and nutrients,” Prof. Pandolfi says.

“The fossil record tells us that sea life  is very resilient – that it recovers after one of these huge setbacks.  But also that it can take millions of years  to do so.”

The researchers wrote the paper out of  their concern that the oceans appear to be on the brink of another major  extinction event.

“There may be still time to act,” Prof.  Pandolfi says. “If we understand what drives ocean extinction, we can also  understand what we need to do to prevent or minimise it.

“We need to understand that the oceans  aren’t just a big dumping ground for human waste, contaminants and CO2 – a  place we can afford to ignore or overexploit. They are closely linked to our  own survival, wellbeing and prosperity as well as that of life on Earth in  general.

“Even though we cannot easily see what  is going on underwater, we need to recognise that the influence of 7 billion  humans is now so great it governs the fate of life in the oceans. And we need  to start taking responsibility for that.”

He adds “The situation is not hopeless.  If fact we have seen clear evidence both from the past and the present that sea  life can bounce back, given a chance to do so.

“For example, in Australia we have  clear evidence of that good management of coral reefs can lead to recovery of  both corals and fish numbers.

“So, rather, our paper is an appeal to  humanity to give the oceans a chance.

“In effect, it says we need to stop  releasing the CO2 that drives these massive extinction events, curb the  polluted and nutrient-rich runoff from the land that is causing ocean ‘dead  zones’ manage our fisheries more sustainably and protect their habitat  better.

“All these things are possible, but  people need to understand why they are essential. That is the first step in  taking effective action to prevent extinctions.”

Their  paper Extinctions  in ancient and modern seas by Paul G. Harnik, Heike K. Lotze, Sean C.  Anderson, Zoe V. Finkel, Seth Finnegan, David R. Lindberg, Lee Hsiang Liow,  Rowan Lockwood, Craig R. McClain, Jenny L. McGuire, Aaron O’Dea, John M.  Pandolfi, Carl Simpson and Derek P. Tittensor appears in the online edition of Trends in Ecology and Evolution (TREE).