Damage to natural services provided by oceans could cost the world $2tr a year by the end of the century if steps to curtail climate change are not taken, a study by the respected Stockholm Environment Institute (SEI) said today.

Researchers warned that without action global temperatures could rise by 4°C by 2100, leading to acidification, reduced oxygen content, stronger tropical storms and sea-level rises, all of which would in turn threaten fish stocks and other marine life.

The Valuing the Oceans paper warns valuable services provided by the ocean are inadequately integrated into economic analyses and plans, and calls for marine ecosystems to be included in carbon offset schemes.

A new market in “blue carbon” could see investors receive carbon credits for projects protecting mangroves or sea grasses, which contain more carbon than forests but are being degraded far quicker.

Without radical change the tourism industry would incur annual costs of $639bn, while a warmer ocean with less ability to soak up CO2 could cost $458bn, the study showed.

“By 2100, the annual cost of the damages from ‘business as usual’ emissions … is estimated to be $1.98tr, equivalent to 0.37 per cent of future global GDP,” the SEI said.

However, the SEI suggests that with radical measures to put the world on course for a “rapid emission reduction pathway”, temperature rise could be kept to 2.2°C and almost $1.4tr of damages could be avoided.

For example, increases in adaptation costs are estimated at $25bn per year for a 0.5 metre rise in sea levels, but escalate to $270bn per year by 2100 for a two metre rise.

“The cost of inaction increases greatly with time, a factor which must be fully recognised in climate change accounting,” said Frank Ackerman, director of the Climate Economics Group at SEI-US.

The report also calls for world leaders to make the oceans a priority in global sustainability goals, which could be thrashed out at the Rio+20 conference in June, and wants the UN to appoint a High Commissioner for the Oceans.

This could help the world better address an issue with multiple causes and stressors, the report says.

“We must develop an integrated view of how our actions impact the ocean, and threaten the vital services it provides, from food to tourism to storm protection,” said Kevin Noone, director of the Swedish Secretariat for Environmental Earth System Sciences at the Royal Swedish Academy of Sciences, and co-editor of the report.

“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. We want to bridge these gaps and give a holistic view of the value of the ocean.”