Logo of Phnom Penh Post newspaper Phnom Penh Post - Climate change to reduce ocean wildlife by 17%




Climate change to reduce ocean wildlife by 17%

Content image - Phnom Penh Post
On current trends, climate change by century's end will empty the oceans of nearly a fifth of all living creatures, measured by sheer weight. AFP

Climate change to reduce ocean wildlife by 17%

Climate change is set to empty the ocean of nearly a fifth of all living creatures, measured by mass, by the end of the century, researchers have calculated.

In a world that heats up three to four degrees Celsius compared to pre-industrial levels, 17 per cent of marine biomass – from minuscule plankton to 100 tonne whales – will be wiped out, they reported in the US Proceedings of the National Academy of Science.

To date, Earth’s surface has warmed a full degree.

Bigger fish and marine mammals already devastated by overfishing, pollution and ship strikes will see especially sharp declines due to rising temperatures.

Even in a “best-case” scenario of limiting warming to 2 degrees Celsius – the cornerstone target of the Paris climate treaty – the ocean’s biomass will drop off by five per cent.

Shallow-water corals, which harbour 30 per cent of marine life, are forecast to disappear almost entirely under these conditions.

Every additional degree will see the ocean biomass shrink by another five per cent. Earth is currently on course to be around 4C hotter by 2100.

“The future of marine ecosystems will depend heavily on climate change,” said Junne-Jai Shin, a biologist at the French Institute for Development Research and one of 35 experts from a dozen countries contributing to the study.

“Measures to protect biodiversity and fisheries management will need to be revisited.”

Fortunately for life on land, oceans – which cover 70 per cent of Earth’s surface – consistently absorb more than 20 per cent of the greenhouse gases humanity spews into the atmosphere.

But the accumulation of all that carbon dioxide has also made ocean water more acidic, threatening to upset the delicate balance of the marine food web.

‘Dead zones’

Some regions will be hit much harder than others, the study found.

Climate change will reduce marine biomass by 40 to 50 per cent in tropical zones, where more than half-a-billion people depend on the ocean for their livelihood, and two billion use it as their main source of protein.

At the same time, the concentration of life at the poles would likely increase, potentially offering new sources of food.

The global population is set to expand from 7.3 billion today to nearly 10 billion in 2050, and to 11 billion by 2100, according to the UN.

“Up to now, the biggest threat has been overexploitation and the use of destructive fishing gear,” said Callum Roberts, a marine conservation biologist and oceanographer at the University of York in England.

“But now, the biggest impact is switching over to climate change, and that is playing out in the sea.”

The number of damaging marine heatwave days has increased by more than half since the mid-20th century, according to a recent study in Nature Climate Change.

“Just as atmospheric heatwaves can destroy crops, forests and animal populations, marine heatwaves can devastate ocean ecosystems,” said lead author Dan Smale, a researcher at the Marine Biological Association in
Plymouth, England.

A 10-week ocean heatwave off western Australia in 2011, for example, shattered the local underwater ecosystem and pushed commercial fish species into colder waters.

A year-long marine heat spell off the coast of central and northern California – known as “the blob” – killed off larges swathes of seagrass meadows and kelp forests, along with the fish and abalone that depend on them.

Another consequence of higher air temperatures is to thicken the ocean’s top layer of warmer water, which results in oxygen-depleted zones bereft of life, Roberts explained.

These “dead zones” are also caused by nitrogen-rich runoff from agriculture around estuaries and along coastal areas.

Researchers at Louisiana State University estimated this week that a dead zone spreading at the mouth of the Mississippi River will cover a 23,000sq km area, and will be the second largest ever recorded in the northern Gulf of Mexico.

MOST VIEWED

  • All inbound flights set to face added scrutiny

    Ministry of Health spokesperson Or Vandine said on Monday that the ministry is monitoring all inbound flights, after it was announced that only those from Malaysia and Indonesia will be temporarily cancelled from August 1. Vandine said on Monday that the two countries were identified as

  • Flights from Indonesia, Malaysia cancelled

    A Ministry of Health official has warned of the possibility of Covid-19 spreading through community transmission after the total infected cases in the Kingdom rose to 225. Ministry spokeswoman Or Vandine told reporters on Saturday that the possibility of community transmission cannot be overlooked and that

  • Man in quarantine dies of ‘overdose’

    The Ministry of Health on Thursday said a Cambodian migrant worker who died while being isolated at a quarantine centre in Tbong Khmum province’s Kroch Chhmar district may have died from syncope or overdose of tablets. In a statement, the ministry said the 21-year-old

  • Ministry set to reopen 20 schools in August

    The Ministry of Education, Youth and Sport will allow 20 high-safety-standards schools to reopen next month despite new cases of Covid-19 in the country. Ministry spokesperson Ros Soveacha wrote in a Telegram message on Wednesday that the schools are in Phnom Penh, Siem Reap and Battambang.