"Today I have signed the instrument of ratification of the Kyoto Protocol," Rudd, the Labour Party leader, said in a statement hours after taking oath as the 26th Prime Minister of the country.

"This is the first official act of the new Australian government, demonstrating my government's commitment to tackling climate change," said Rudd, who came to power ousting Conservative leader John Howard in elections nine days ago.

Rudd, who had promised during his campaign to reverse the previous government's policy and ratify the Kyoto pact, said the ratification was considered and approved by the first executive council meeting of the government this morning.

"The Governor-General has granted his approval for Australia to ratify the Kyoto Protocol at my request," he said.

Under United Nations guidelines, ratification comes into force 90 days after the instrument of ratification is received by the UN, which means Australia will be a full member of the Kyoto Protocol by the end of March 2008.

Rudd said the Kyoto Protocol was considered to be "the most far-reaching agreement on environment and sustainable development ever adopted."

"Australia's official declaration today that we will become a member of the Kyoto Protocol is a significant step forward in our country's efforts to fight climate change domestically -- and with the international community," Rudd said.

Today's move by Australia leaves the US as the only major developed nation that did not ratify the global treaty.

Rudd said the federal government would do everything in its power to help Australia meet its Kyoto obligations, including setting a target to reduce greenhouse gas emissions by 60 per cent of 2000 levels by 2050.

It also would establish a national emissions trading scheme by 2010 and set a 20 per cent target for renewable energy by 2020.

Rudd will undertake his first foreign tour as Prime Minister next week when he travels to the Indonesian resort island of Bali for the opening of the high-level segment of a international conference on climate change.