Australian Prime Minister Kevin Rudd urged the United States on Tuesday to take more action on climate change and become more involved in the global debate on the issue.

As the only developed nation not to sign the greenhouse gas-controlling Kyoto Protocol, America's stance on climate change has made it easier for major developing countries to avoid acting, Rudd told the Australia-New Zealand Climate Change and Business Conference in the northern city of Auckland.

"I think our first step should be to get the United States of America fully engaged," Rudd said.

He said he has spoken about climate change policy with the U.S. presidential candidates, Republican John McCain and Democrat Barack Obama.

"What is heartening on that question is that both candidates ... have indicated that they will be moving on this, and with an ambitious set of targets," he said.

A Nobel prize-winning panel of U.N. scientists has said greenhouse gas emissions must level off within the next 10-15 years and then start to dramatically decline to avoid a rise in average temperatures that could have catastrophic consequences.

They warn that an increase of more than 3.6 degrees Fahrenheit could lead to a rise in sea levels threatening coastal areas, and the extinction of up to 30 percent of the planet's species.

New Zealand Prime Minister Helen Clark, who joined Rudd on stage, said American actions were important even if they did not sign global climate treaties.

If the U.S. did join the Kyoto system following the presidential election, its involvement would take away excuses for inaction from developing countries like China and India, she noted.

"There is no way the First World can solve this problem alone _ even if the United States comes in," she said.

Much rested on developed economies leading by example, she said, adding, "That is why Australia coming in (to the Kyoto Protocol) is critical." The Rudd government signed the protocol within days of taking office.