"Climate change must be a foreign policy priority," the New Zealand prime minister said during an address in Sydney to the Lowy Institute.
Well-founded concerns over the militarisation of the Pacific should be matched with a focus on the violence of climate change, she said on Thursday.
"All of this needs to happen because ultimately, this is our home," Ms Ardern said.
"And that makes you our cousins.
"But more importantly, over many years, it has made you our friend."
She referred to Australia as New Zealand's largest trading partner, its only formal ally, its largest market for foreign investment and the place where 40 per cent of foreign arrivals in New Zealand landed in 2019.
"It's lucky we like you so much," she said.
"We share our people, our problems and our solutions.
"When we look to our principles, co-operation, values and place, we naturally find you within them.
"We won't always agree, and nor should we.
"But it's true that in the messy world we live, friendship matters."
New Zealand had committed $1.3 billion to climate change, with at least 50 per cent of that spend going to the Pacific, she said.
The Pacific Island Forum (PIF) could play a role establishing climate mitigation projects, where foreign aid could be directed.
Ms Ardern and Prime Minister Anthony Albanese will attend the PIF next week.
"Not every external aid and development donor will have the capability to access our neighbours individually," she said.
"We need to look to the role we can play to bring in that support on the terms the Pacific sets, and the PIF is a great way to do that."
Later on Thursday Ms Ardern will hold talks with Premier Dominic Perrottet at NSW parliament, as she continues an Australian visit aimed at strengthening trade and security ties.
On Friday, Ms Ardern will see Mr Albanese after they briefly met shortly after the Australian federal election in May.
The leaders' meeting is expected to cover labour shortages, economic links, regional security, Indigenous co-operation, migration, economic recovery and climate change.
Both have recently been overseas, attending a NATO summit in Spain to which Australia and New Zealand were invited as part of the Asia-Pacific partners grouping along with Japan and South Korea.
Ms Ardern arrived in Sydney on Wednesday after spending two days in Melbourne, where she met Victorian Premier Daniel Andrews to discuss COVID-19 management, healthcare system pressures and rail infrastructure.
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