Failing to tackle climate change will damage the world's oceans to the tune of £270 billion a year by mid-century, researchers warned today.
A study of the impacts of unchecked carbon emissions and rising temperatures on fisheries, tourism, sea-level rises, storms and the role of the oceans as a store of carbon found costs would rise to almost £1.3 trillion a year by 2100.
But the world's oceans are not just at risk from global warming: they are facing multiple threats such as pollution, dead zones and over-fishing, as well as climate impacts which include the seas becoming more acidic and sea levels rising.
The authors of the Valuing the Ocean study from the Stockholm Environment Institute said the problems could not be tackled one at a time, and called for integrated management of the seas from the local to the global level.
They warned that they had not attempted to put a total price on damage to the oceans, and that their estimate for the costs of failing to address climate change was conservative.
It did not include "priceless" losses so, for example, they were able to analyse the value of whale-watching to the tourism industry but not the value of whales.
And it did not attempt to estimate what would happen if "tipping points" were reached, such as the oceans becoming sufficiently acidic that swathes of organisms which support whole food chains were wiped out.
The study focused on the financial consequences for oceans of failing to reduce emissions, causing projected global temperature rises of 4C, compared to the results of taking action to curb emissions that would limit rises to 2.2C.
It found that by 2050 the losses associated with no action on climate change would be four times greater than the losses suffered if emissions were reduced, 428 billion US dollars (£270bn) compared to 105 billion US dollars (£66bn) .
By 2100 the costs of climate change on the oceans would be nearly 1.98 trillion US dollars a year (£1.25 trillion), compared to 612 billion US dollars (£386bn) if the world curbs carbon emissions.
Fisheries would be damaged by the migration of fish north, low-lying cities would be at risk from sea-level rises and tourism such as diving and snorkelling on Australia's Great Barrier Reef would be hit if ocean environments were damaged.
The researchers warned the worst hit areas would be already poorer places such as Africa, where artisan fishermen could lose their catches, and Asia's low-lying and heavily populated Mekong Delta.
Professor Kevin Noone, of the University of Stockholm and co-editor of the study, said: "The global ocean is a major contributor to national economies, and a key player in the earth's unfolding story of global environmental change, yet is chronically neglected in existing economic and climate change strategies at national and global levels."
He said that the £860 billion difference by 2100 between the costs of inaction and action was less than 1% of gross domestic product (GDP), which might make some people think it is not worth taking action.
But he said: "It is still a lot of cash and it does show that making these investments and trying to avoid these costs is not going to break the bank."
And the director of the Stockholm Environment Institute's climate economics group, Frank Ackerman, said: "These figures are just part of the story, but they provide an indication of the price of the avoidable portion of future environmental damage on the ocean."
He added: "The cost of inaction increases greatly with time, a factor which must be fully recognised in climate change accounting."