Growing global momentum to protect the world’s oceans from overfishing could be undermined by Australia, warns renowned conservationist David Suzuki and more than 1,461 other scientists.

Australia is currently considering the world’s biggest downgrading of a protected area with a reduction in the size of its network of marine reserves.

“If Australia does something progressive in 2012, and then walks back from that, what the hell are we going to expect from international cooperation?” said Suzuki, who described the move as “sickening”.

In 2012 the Australian government created what was then the world’s largest network of marine reserves. The move followed years of consultation, and despite limited protection for the most biodiverse coastal areas, it was welcomed by environmental groups.

Since then, global momentum has been building for marine protection. In 2014 at the once-a-decade World Parks Congress in Sydney, conservation scientists called for fishing to be banned in 30% of each type of marine habitat globally – a call supported two years later by about 90 countries and hundreds of NGOs that are members of the International Union for Conservation of Nature.

In 2016, the US president Barack Obama created the world’s largest marine reserve by expanding an existing ocean reserve off Hawaii. That year he also established a large marine park in the Atlantic Ocean.

Similarly, Chile, France, Kiribati, New Zealand, Russia and the UK have created large areas where fishing is banned.

In contrast, the Australian government recently announced draft plans to reduce by 40% the amount of its marine parks that are “no-take” fishing or construction zones.

According to WWF-Australia, that would represent the world’s largest downgrading of protected areas on record. More than 433,000 sq km would be downgraded to allow commercial fishing – more than half of that in the Coral Sea marine park, adjacent to the Great Barrier Reef, one of the few remaining large parts of the Pacific Ocean still in good health.

Australian waters contain rich biodiversity ranging from the tropics to Antarctica. A statement signed by Suzuki and 1,461 scientists described these waters as a “global asset” and called on the government to increase protections.

“They support six of the seven known species of marine turtles and more than half of the world’s whale and dolphin species. Australia’s oceans are home to more than 20% of the world’s fish species and are a hot spot of marine endemism. By properly protecting them, Australia will be supporting the maintenance of our global ocean heritage,” the statement said.

“It’s absurd to think this is really Australia’s water,” Suzuki told the Guardian. “These oceans belong to the world – you just happen to be the caretakers in that particular area.”

Jessica Meeuwig, director of the Centre for Marine Futures at the University of Western Australia, said Australia’s move set a dangerous international precedent.

“Australia’s move to go backwards undermines that progress,” she said. “In Australia we will be supporting an international benchmark that says we’re happy to have paper parks areas technically set aside but with minimal actual protections.”

Paper parks have been a major concern in the conservation world.

Meeuwig said Australia’s precedent is particularly dangerous given the Trump administration is mulling cuts to protected areas on land and in the ocean.

“Australia will pip Trump to the post,” she said.

The Trump administration is examining 27 protected areas for the rollback of protections, with a leaked memo revealing 10 – including the two marine parks established by Obama – earmarked to allow “traditional uses” such as mining, logging and hunting.

She said Australia’s unwinding of protections would help normalise radical moves to unwind protection in the US, as well as set a poor example for other countries.

“Such a backwards step just gives other countries an excuse to do less. Australia is a developed economy with good governance. If we can’t get this right, all we’re doing is putting the responsibility to protect oceans to nations that have less and are dealing with bigger challenges. That’s not leadership.”

Suzuki, who owns a house in Queensland’s Port Douglas and has spent a lot of time on the Great Barrier Reef, is angry about Australia’s rollback.

“We’re an air-breathing land animal. We’ve trashed the terrestrial environment with vast clearcuts and monocultures of rubber trees and corn and wheat. We’ve used the land and air to spread potent pesticides and toxic compounds. We’ve really fucked up the land that is our ecosystem. And now we go into the oceans that cover 70% of the planet and we’ve trashed that,” he said.

Suzuki said after the devastating bleaching of the Great Barrier Reef in 2016, he visited it and wept.

He said Australia needed to face up to the interconnected issues of climate change and ocean health, both of which it was failing to address.

“I’m sorry Australia, wake up,” Suzuki said. “The oceans are a mess and a great deal of the mess is a reflection of climate change. Climate change is the overarching issue that is hammering the oceans as well as terrestrial areas. And it is absolutely disgusting that coal is still considered a great economic input to Australia.

“When you’ve got something that [other countries] would die for – you’ve got sunlight up the ying yang, why isn’t Australia the world leader in this incredible form of energy? It makes me sick. You’ve got great research facilities. You’ve got great scientists. You’ve got everything going to be a world leader in the energy of the future and you’re not doing it. And it’s not surprising then that you are doing the same to the oceans. What is it going to take for Australia to wake up to the opportunities?”