Vanuatu's Special Envoy for Climate and Environment says he is "obviously disappointed" by the Australian government's statement during the International Court of Justice (ICJ) proceedings regarding legal obligations of nations in relation to climate change.
Australia has taken a different view from Vanuatu and other Pacific Island nations.
On Monday, Australia argued that the United Nations Framework Convention on Climate Change (UNFCCC) and the Paris Agreement are the primary sources of international obligations to address greenhouse gas emissions.
Vanuatu seeks to hold polluting countries to account
Regenvanu said he was disappointed by Australia's position, along with what was shared from the United States, Saudi Arabia, and China.
"These nations, some of the world's largest greenhouse gas emitters, have pointed to existing treaties and commitments that have regrettably failed to motivate substantial reductions in emissions," Regenvanu said in a statement.
"It is particularly concerning that some of these nations, upon whom we depend for aid and support, have not acknowledged the severity of the crisis or their responsibilities under international law.
"Our dependency on their assistance makes it all the more critical for them to act responsibly and in solidarity with vulnerable nations like ours."
He hopes that former colonial powers, France and the United Kingdom, will instead back Vanuatu.
Greenpeace Australia Pacific's general counsel Katrina Bullock said Australia's position "completely undermined its Pacific neighbours".
"It disregards decades of international human rights legal developments and directly contradicts the powerful legal submissions of Pacific, African, and Caribbean nations."
Australia has put in a bid to host COP31 in partnership with the Pacific.
The country, along with United States, is also trying to reassert its influence in the Pacific, as China becomes more involved in the region.
The ICJ will decide on two questions: What are the obligations of states under international law to protect the climate and environment from greenhouse gas emissions?
And, what are the legal consequences for states that have caused significant harm to the climate and environment?
Fiji was the last Pacific island nation to give its submission on Wednesday.
The country's Attorney-General Graham Leung said land and resources are becoming increasingly vulnerable.
"Is it just that our people are forced to abandon their ancestral lands and heritage because of the inaction of those most responsible for climate change, is it? How do we protect the future of our people?" Leung asked the court.
He said international law requires states to not cause trans boundary harm and this also applied to greenhouse gas emissions.
"No state has the right to use its territory in a way that causes significant harm to another state."
Vanuatu started the proceedings with Regenvanu who told the ICJ countries conduct are on trial for consistently failing to rein in emissions.
"I must emphasis that since 1990 emissions have increased by over 50 percent reaching an all time high in 2023 last year, more than half of all CO2 emissions since 1750 were emitted after 1990, whatever the timeframe, there is no excuse."
The United Nations climate meeting COP29, which wrapped up last month in Baku, Azerbaijan, was labelled disappointing for the Pacific and developing countries.
Regenvanu said the Baku summit was another example of the process failing.
"The prolonged and systematic failure of the COP has cost them [Vanuatu people] their wellbeing, their cultures and even their lives.
"There is an urgent need for a collective response for climate change grounded not in political convenience but in international law."
The case landed in the ICJ after campaigning from Vanuatu students.
Pacific Islands Students Fighting Climate Change - the group which initiated the campaign - president Cynthia Houniuhi said UN negotiations had been hijacked by major fossil fuel producers.
"As judges of the world court you possess the power to help us course correct and renew hope in humanities ability to address the greatest challenge of our time and you can do this simply by applying international law to the conduct responsible for climate change," Houniuhi from Solomon Islands said.
The Pacific Community's (SPC) director of climate change Coral Pasisi said during an online press conference that legal opinions from the ICJ can serve as a catalyst for international law's being developed to correct injustices.
"We know that a legal opinion is not legally binding but we do know a legal opinion from the International Court of Justice has a very strong moral weighting."