Former Australian Prime Minister Tony Abbott has pushed for during a Hungarian demographic summit aimed at promoting the "traditional family model".
During his speech, Mr Abbott praised Hungary's nationalist Prime Minister Viktor Orban and warned Europe against the "military-age male" migrants "swarming" their shores.
He also criticised Prince Harry and Meghan Markle for announcing they would only have two children because of the human contribution to climate change.
"Members of the royal family are entitled to have as few or as many children as they choose. But having fewer children in Western countries will hardly make the climate better given all the children that will be born elsewhere," he told the crowd in Budapest, which included political and religious leaders.
Hungarian Prime Minister Viktor Orban with Tony Abbott in his office in Budapest. Source: Hungarian Prime Minister's Office
"It will, though, certainly make Western countries smaller and the economy weaker too."
"Size matters," Mr Abbott said, explaining that the problem facing the West was that it is that other countries are getting "bigger and richer faster".
While praising migration as a fundamental part of Australia's history, he said that increased migration from non-Western nations combined with decreasing birth rates would result in a "new world order".
The Budapest Demographic Summit, which took place over 5 and 6 September, also featured speeches from Mr Orban, Czech Prime Minister Andrej Babis and Serbian President Aleksandar Vucic.
During the summit, Mr Orban called on European leaders to encourage people to have more children and reject migration as a solution to shrinking populations.
"If we accept migration as a solution then we are contributing to population replacement," Mr Orban said, using a loaded term used in extreme-right wing circles.
Since winning a third consecutive term in power last year, Mr Orban has reframed his government's policies as "Christian democracy".
Mr Abbott, who was photographed alongside Mr Orban on multiple occasions, said he supported the Hungarian leader's focus on families.
Mr Orban and Mr Abbott on the prime minister's balcony in Budapest. Source: Hungarian Prime Minister's Office
The former prime minister and notable climate change sceptic, who lost his long-held seat of Warringah in the May federal election, disputed that greenhouse gases were a significant threat to humanity.
"It seems to me that it is not so much our failure to reduce carbon dioxide emissions, but our failure to produce children that is the extinction reality against which we really need to work against," he said.
"It does take rare political courage to defy political correctness enough and go forth and multiply."
The speech comes three days after Mr Abbott told an event in the UK that Britain should set a cap on skilled migration to avoid being "swamped" by migrants after Brexit.
During the event, the former prime minister also praised UK Prime Minister Boris Johnson as the "people's champion".
"You'd probably have to put a cap on numbers because Britain is such a desirable location and you don't want the place swamped with people trying to make a new life here," he said.
