UN finds that star power works as celebrities focus attention on world issues

Leonardo DiCaprio's speech for action on global warming was seen by 1,143,167, President Obama's by 15,

Leonardo DiCaprio was in New York to get his message across (AFP)

The only thing missing at the United Nations headquarters in New York is a theatre marquee over the entrance. Last week it would have been lit up with more names than you'd find in a double issue of the Radio Times. "Emily Watson, Leonardo DiCaprio, with Victoria Beckham and Idris Elba! Special matinee performances!!"

Tapping celebrities has long been a tradition at the world body. Danny Kaye became its first Goodwill Ambassador promoting the UN Children's Fund, Unicef, in 1954. But in the era of social media, where megaphone wattage can depend on Twitter followings, their usefulness is greater than ever.

Few of us will have missed that Leonardo DiCaprio led New York's march for action on global warming last Sunday and opened the UN's Climate Summit on Tuesday alongside the UN Secretary-General, Ban Ki-moon. That is thanks, in part, to Twitter and YouTube, but also his debuting on Instagram for the occasion. In under four days, he went from zero followers on the photo-sharing app to almost 300,000.

None of the presidents and potentates filling UN headquarters for the annual meeting of its General Assembly last week received such attention. Emma Watson came to launch the "HeforShe" campaign, urging men to do more to support equal rights for women, Ms Beckham was introduced as a new Goodwill Ambassador for UNAids, while Idris Elba, whose parents are from Sierra Leone, joined the emergency session on Ebola.

Sometimes this "celeb-isation" can backfire. When the singer Christina Aguilera returned from a visit to Rwanda for the World Food Programme she gave an interview describing the country as "war-torn" (it hadn't been for 20 years). She also released what many saw as a self-serving video of her visit with her own music as the soundtrack.

But the reach of the famous remains vital for the UN and NGOs. "People who have profile can get things on the agenda... and that's the reality," says Adrian Lovett, an executive director of One, the global advocacy group foundedby U2's Bono.

At the UN, no one sees it more plainly than Jeff Brez, head of NGO Relations and Advocacy. He points to the YouTube clip of DiCaprio's speech at the start of the Climate Summit which was viewed 1,143,167 times in three days. President Barack Obama's clip had just 15,000 views. DiCaprio recently joined the exclusive "Messengers for Peace" club. There are only 12, all selected by the Secretary-General. Others include Stevie Wonder, Mia Farrow, Michael Douglas and cellist Yo-Yo Ma. Another is the author Paulo Coelho, who has 9.49 million Twitter followers.

The magnification of the effectiveness of all the ambassadors by social media has been profound, says Mr Brez. "Twenty years ago, DiCaprio would have had media coverage, a great article in a newspaper. Now, you have this incredible access of social media and its video side."

"Bono and others like him would be the first to say it's pretty crazy that anyone should listen to a celebrity before they listen to anyone else," Mr Lovett added. "But that is a fact of life."