Selwin Hart, the special adviser to UN secretary-general António Guterres on climate action, said Australia had not met the threshold needed to speak.
“We will not be commenting on the participation of individual leaders,” he said.
“But the three co-hosts – the UN, UK and France – provided all member states with very clear guidance from the outset that speaking slots would go to countries and other actors who show the most ambition right now.”
Hart would not be drawn on what the UN thought of Morrison’s planned announcement or what the UN wanted to see from Australia on climate change.
However he did repeat the UN’s position that countries should sign up to achieving net zero emissions by 2050 ahead of a major climate summit in Glasgow next November.
Morrison has recently embraced the idea of net zero emissions but has only said it can be achieved in the second-half of the century.
New Zealand Prime Minister Jacinda Ardern was also excluded from the list of nearly 80 world leaders given permission to address Saturday’s summit.
China, which is building dozens of new coal-fired power plants, was given a spot.
“Rather than focussing on those countries that are not on that list as of now, we really should be celebrating those that have decided to come forward this early – many of them from the developing world who despite the challenges of the pandemic, [are] on the frontlines of the climate crisis including many countries in the Pacific – to make bold and ambitious commitments around net zero,” Hart said.
“Some have brought these commitments forward and I think we should celebrate those leaders who have come forward and decided to take this ambitious step before COP26.
“We have a long way to go before Glasgow and we hope that this coalition around net zero by mid-century will grow.”
Johnson offered Morrison the chance to speak even though France, the UN and other supporting partners like Italy and Chile had a say on who made the final list.
The government is furious that Johnson was unable to guarantee the promise. There had already been tensions between the UK and Australia over climate in the weeks since Downing Street publicly claimed Johnson had urged Morrison to take “bold action” during a phone call on October 28.
“He has thrown us under the bus,” one government official said on Thursday.
Downing Street did not respond to questions on Thursday.
Diplomatic sources not authorised to speak publicly said Britain’s Foreign, Commonwealth and Development Office was determined to not let Australia speak.
Morrison plans to outline his climate policy to an online meeting of the Pacific Islands Forum on Friday night instead.
He told Parliament on Thursday that Australia’s climate and energy policy would be set in Australia’s national interest, “not to get a speaking slot at some international summit”.
Japan, Fiji, Kiribati, Nauru and Cambodia are the only countries in the Asia-Pacific region given a speaking slot.
Hart said the UN wanted to see more commitments on climate financing and appeared to take a swipe at Australia for not doing more to help its Pacific neighbours.
“Ten years ago developed countries promised to mobilise $US100 billion per year in new climate finance to support mitigation and adaptation in the developing world,” he said.
“That goal has not yet been met and therefore its absolutely crucial that as we head towards Glasgow there is renewed commitment around climate finance mobilisation for the developing world as well as support for those countries -including many in the Pacific that are already dealing with climate disruption and who face and uncertain future as a result of the climate crisis.”
Morrison last year pledged to redirect more than half a billion dollars in foreign aid towards renewable energy projects and disaster relief throughout the Pacific.
Bevan Shields is the Europe correspondent for The Sydney Morning Herald and The Age.