Climate change is not sexy. Leonardo DiCaprio, on the other hand, is rather easier on the eye than maps, charts and graphs of rising temperatures and sea levels.

As DiCaprio has been named a Messenger of Peace by the UN to work on promoting Climate Change, ahead of the UN Climate Summit next week, here's a reminder of some of the other Hollywood stars the UN has called upon to help make unsexy causes decidedly more pin-upable.

1. 

   Currently the heroine of humanitarian causes, Angelina Jolie has been a special envoy to the UN High Commissioner for Refugees since 2012, after a decade as a goodwill ambassador. She first understood the consequences of conflict when filming Lara Croft: Tomb Raider in Cambodia. This year she also joined forced with former foreign secretary William Hague to speak out against sexual violence in conflict. As special envoy she outranks her fellow a-listers below.

2. Nicole Kidman became a goodwill ambassador for UNICEF in 1994 and for UNIFEM (UN Development Fund for Women) in 2006. She has spoken out on violence against women and fundraised for a number of causes supporting women's and children's health.

3. 

   A newcomer to the UN brigade, Emma Watson was appointed as UN Women's goodwill ambassador in July this year. The organisation is focussed on working for gender equality, and Watson is the face of the HeForShe campaign launching tomorrow, bringing men and women together to recognise the inequalities women face around the world.

4. Michael Douglas is a veteran UN messenger of peace, having been first designated in 1998. His focus area is disarmament, and he has worked to raise awareness of the need for greater controls on light weapons. He is on the board of the anti-war grant foundation, the Ploughshares Fund.
5. Screen siren and activist Charlize Theron set up the Charlize Theron Africa Outreach Project in 2007. The organisation works to combat the spread of HIV/AIDS among young people, particularly in her home country, South Africa. Theron was made a UN messenger of peace in 2009, focussing on the prevention of HIV and the elimination of violence against women.

6. 

   In April, George Clooney stepped down from his UN messenger of peace role, citing other professional commitments. He was appointed in 2008, having worked to raise the profile of the suffering of refugees in Darfur, Sudan and founded the non-profit organisation Not On Our Watch. A high point of his activism for this cause was being arrested for protesting outside the Sudanese embassy.

7. Among the conservation-minded stars is Edward Norton, who was made a UN goodwill ambassador for biodiversity in 2010. Norton is president of the Maasai Wilderness Conservation Trust, and ran the 2009 New York City marathon for the trust. He is also on the board of a non-profit organisation developing affordable housing that was founded by his grandfather.
8. Queen of the romantic comedy, Drew Barrymore became an ambassador against hunger for the World Food Programme in 2007, having visited WFP projects in Kenya. Her travel diaries from the trip were published in Marie Claire.
9. Though not an ambassador or messenger (yet), in 2013 UNICEF awarded Matt Damon for his conservation and sanitation, having set up Water.org in 2009. Damon is also a co-founder of Clooney's Not On Our Watch, and supports numerous humanitarian campaigns.

10. 

    Last but not least, Leonardo DiCaprio has earned his new position having set up the Leonardo DiCaprio foundation in 1998, supporting conservation and humanitarian projects around the world. He also created, produced and narrated the documentary 11th Hour, about the crisis facing our environment. Speaking about his new role he said: "I feel 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."