Get off your phone Helen - and start talking to Leo

The former Prime Minister was snapped sitting alongside Oscar-winning actor Leonardo DiCaprio during the signing of the Paris Agreement on climate change. Photo / AP

Helen Clark's campaign to win the United Nations' top job might have received the ultimate celebrity backing.

The former Prime Minister was snapped sitting alongside Oscar-winning actor Leonardo DiCaprio during the signing of the Paris Agreement on climate change at the United Nations' HQ in New York overnight on Friday.

DiCaprio has been one of the leading celebrities pushing for action on global change and in 1998 launched the Leonardo DiCaprio Foundation aimed at protecting threatened ecosystems and ensuring the long-term health and well-being of all Earth's inhabitants.

In September 2014 he was also appointed a United Nations' Messenger of Peace.

DiCaprio spoke at the signing of the Paris Agreement, telling representatives of more than 170 governments that his travels with his foundation and the UN had reinforced to him the "crisis" the world faced. "All that I have seen and learned on this journey has terrified me," he said.

"There is no doubt in the world's scientific community that this is a direct result of human activity and that the effects of climate change will become astronomically worse.

"I do not need to throw statistics at you. You know them better than I do and, more importantly, you know what will happen if this scourge is left unchecked. You know that climate change is happening faster than even the most pessimistic of scientists warned us decades ago. It has become a runaway train bringing with it impending disaster for all living things."

Climate Change Minister Paula Bennett signed the historic global climate change agreement on behalf of New Zealand. Member nations committed to reducing their country's emission rates by 2030, and New Zealand committed to reducing emissions to 30 per cent below 2005 levels.

Clark recently launched her campaign to succeed Ban Ki-Moon as the United Nations' Secretary-General. If successful, she will be the first woman to hold the post.

The New Zealand Government has nominated Clark and is helping to fund her tilt, a campaign cost set to run into the hundreds of thousands of dollars.