Officials from the climate change department joined ministers and their staff for November's COP30 in the Brazilian city of Belem, where the federal government attempted to negotiate the hosting rights for the 2026 event.
Australia ultimately failed to win the 2026 conference, ceding the rights to Turkey after a months-long diplomatic stalemate.
The cost of flying 42 departmental officials to the gathering in Brazil was $1.6 million, Department of Climate Change secretary Mike Kaiser told a parliamentary hearing on Monday.
"Belem is not a destination that officials of this department frequently fly to," he said.
"Some officials needed to plan four or up to five flights to get from Australian locations to Belem."
Mr Kaiser said the figure was "indicative" and based on internal budgets, because the final number was not yet available.
In total, 75 officials attended the conference at various stages.
That included the 42 departmental workers, ministers, their staff and diplomats, some of whom were already stationed in Brazil.
Australia's pavilion at this year's event is estimated to have cost $1.4 million - a figure officials said was in line with previous climate conferences.
The government said Australia held more than 90 events during the conference, hosting at least 4500 participants.
The committee also heard Australia could be on the hook for millions of dollars in bills to consultants, labour hire companies and lawyers linked to the failed COP31 hosting bid.
Because the conference was fast approaching without a host locked in, government officials had begun planning for it to be held in Adelaide.
COP31 operations division head Andrew Hutchinson told parliament's environment and communications committee the government had committed $7.5 million before withdrawing from the hosting bid.
The climate change department was now working to wind up the contracts, he said.
"We'll of course be trying to leverage value out of those contracts," Mr Hutchinson told the inquiry on Monday.
"By and large, you would expect most of those contracts to close as soon as we're able to under the terms of that contract."
It's unclear whether the government will be able to recoup any of the $7.5 million it committed.
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