Leonardo DiCaprio’s global fame and passion for the planet has earned him a starring role at the United Nations climate summit in New York next week. U.N. Secretary-General Ban Ki-Moon tapped the actor to be the organization's representative on climate change and to address the opening of the Sept. 23 event.

“Mr. DiCaprio is a credible voice in the environmental movement, and has a considerable platform to amplify its message,” Ban said in a statement. “I am pleased he has chosen to add his voice to U.N. efforts to raise awareness of the urgency and benefits of acting now to combat climate change.”

DiCaprio joins an ever-growing stable of celebrities and public figures appointed to endorse U.N.-aligned causes. The idea is that their global popularity and household recognition can inspire the public to take action -- through fundraising or pressuring politicians -- on everything from human rights campaigns, women’s health initiatives, international aid and environmental protection.

The U.N. has now appointed over a dozen Messengers of Peace, including primatologist Jane Goodall, Holocaust survivor Elie Wiesel and renowned musicians and actors such as Stevie Wonder, Yo-Yo Ma and Charlize Theron. A similar camp, the Goodwill Ambassadors, has nearly 200 members, the latest of which includes Harry Potter star Emma Watson.

“Any time you expect to bring something to action, you’ve got to start with conscious raising,” Robert Thompson, a pop culture expert at the S.I. Newhouse School of Public Communications, said in an interview. “Celebrities are good at conscious raising; if a celebrity talks, microphones are there to record it. An appointment like [DiCaprio’s] is a way to get people to pay attention.”

Whether celebrity endorsements can translate into tangible results is difficult to gauge. But Paul Brewer, a communications professor at the University of Delaware, said that stars who work behind the scenes with politicians and organizations are the most influential because the public considers them credible.

Actress Angelina Jolie is a prominent example. As a special envoy to the U.N. High Commissioner for Refugees, Jolie regularly tours refugee camps to bring attention to the plight of displaced people. Most recently, she visited a naval rescue base in Malta, off the coast of Sicily, amid news that thousands of migrants from Syria, Egypt, Libya and Sudan have drowned or gone missing while attempting to cross the Mediterranean Sea.

“She is incredibly well trained, has a number of professional people counseling her and she has proven she is willing to take risks,” Andrew Cooper, a distinguished fellow at the Center for International Governance Innovation, previously told the New York Daily News.

Actor George Clooney helped to thrust the genocide in Darfur, Sudan, into the global spotlight when he produced a 2006 documentary about it and joined the Save Darfur Coalition. Yet for some, Clooney represents a case of celebrity activism gone awry. Critics accused Clooney and other advocates of over-simplifying the Sudanese conflict and greatly exaggerating the number of people killed, all while championing policy solutions that some said could do more harm than good. Hollywood doesn't seem to mind; earlier this week, it was announced that Clooney will receive the Cecil B. DeMille Award at the Golden Globes for his humanitarian work in Darfur. Meanwhile, recent reports indicate that violence is returning to Darfur amid a chaotic peacekeeping mission.

DiCaprio’s environmental campaign will likely prove far less controversial. The 39-year-old actor’s eponymous foundation focuses on protecting biodiversity, conserving forests and oceans and tackling the climate change challenge. In June, DiCaprio joined President Obama in pledging to protect the oceans, saying his foundation would spend $7 million over the next two years to support expanding marine reserves and other conservation initiatives.  

As a U.N. climate representative, DiCaprio said he feels “a moral obligation to speak out at this key moment in human history -- it is a moment for action. How we respond to the climate crisis in the coming years will likely determine the fate of humanity and our planet,” according to a statement.

DiCaprio will join more than 120 world leaders at the Tuesday summit. Ban said he called the special event -- which is being held on the sidelines of the U.N. General Assembly’s annual ministerial meeting – to promote global efforts to curb greenhouse gas emissions ahead of formal climate negotiations in Paris in 2015.

The secretary general separately announced he will join the People’s Climate March on Sunday, which organizers say could be the largest public action on climate change. The step is unusual, as high-ranking officials do not normally attend mass public protests, the Guardian noted. “I will link arms with those marching for climate action,” he told a press conference this week. “We stand with them on the right side of this key issue for our common future.”