First catch the attention of Leonardo DiCaprio, then change the world. It's a lot to ask, but Brittany Trilford is already half way there.

On Thursday she is one of the opening speakers, with a five minute address to 130 heads of state at the Rio+20 Earth Summit. She was selected after an impassioned video that impressed a jury including Hollywood heavyweights DiCaprio and Don Cheadle.

"It's very exciting, it's very nerve-racking, but I think I can handle it," the 17-year-old Queen Margaret College pupil says. "I think the excitement will outweigh the nerves on the day."

She is taking her ambassadorial role seriously and aims to keep leaders at the United Nations Conference on Sustainable Development honest as they discuss jobs, energy, sustainable cities, food security and sustainable agriculture, water and oceans.

"The system we use to manage this planet has never been sustainable," Brittany says.

"A growing number of people all over the world realise that it's broken, and the quick-fixes our governments try to get away with are just not good enough. The solutions for the future we want have been available for a long time – only the political will for real change is still missing.

"I feel honoured to take up my obligation to stand up, be counted as one of my generation, and strengthen the voice of youth at Rio+20."

She won her Brazilian engagement on the strength of her entry in a global youth video competition, and intends to make the most of her opportunity.

"I'll just be like a sponge, absorbing everything," she says.

While in Rio, she will get the chance to grill influential thinkers and policy makers as she attends the series of side events on offer in the leadup to the summit proper.

Her schedule includes meetings with European Union climate commissioner Connie Hedegaard and former prime minister and UN Development Programme administrator Helen Clark.

She will also meet Severn Suzuki, "the girl who silenced the world for six minutes" after her speech at the original 1992 Earth Summit in Rio as a 12-year-old.

Severn, now a married mother, began her speech with the words "no hidden agenda" and received a standing ovation at the end. Some delegates wept and her words had such an impact that she became a regular at UN conferences.

Brittany, as a representative of youth on the global stage, says she "most definitely" feels a responsibility towards the planet's three billion young people, although she admits she can't represent everyone.

"I'm not speaking on behalf of them, I'm speaking as a global citizen. There are lots of views I need to take into account so I'm taking a more diplomatic outlook on the way I express my views ... it's a huge responsibility, but I love it."

Last month a World Wildlife Fund report criticised successive New Zealand governments for failing to live up to promises made at the original 1992 summit – a document she'll struggle to defend.

"The report was very shocking. It looks pretty dire and gives a pretty negative view of what's been happening here in New Zealand, but I'm a very proud New Zealander and I think on the whole we are making more progress comparatively to other countries in the world."

The Rio summit has already attracted criticism as another toothless talkfest, but Brittany says it is this type of cynicism and negativity that is holding up the race to build a sustainable planet.

She wants leaders to look youth "in the eye" and be accountable to the next generation. "We're the next set of voters, the next set of leaders ... we're the future really."

New Zealand's delegation to Rio will be led by Environment Minister Amy Adams, and will include officials from the ministries of Environment, Primary Industries and Foreign Affairs and Trade, as well as industry, iwi and non-government delegates.

The Future We Want

Young New Zealanders are shunning the image of their country as a clean, green paradise and want decision-makers to stand up and listen to their concerns, a new Unicef report shows.

The Future We Want consulted 52 New Zealanders aged between 14 and 26 in Auckland, Wellington and Christchurch, gauging their views in the leadup to the Rio+20 Earth Summit. The report found that young Kiwis:

Rejected the notion of the "quarter-acre pavlova paradise". New Zealand faces a raft of environmental, social and cultural issues, which are often ignored by policy makers, including excessive use of water (domestically and commercially) and the need to improve energy efficiency.

Felt let down by their representatives and said their right to contribute to conversations about the future of New Zealand was not being upheld.

Put a high value on shared commons such as public spaces, oceans and waterways and believed they should be sustained for future generations.

Thought trade should be "fair not free", with producers paid fairly for their work. Green and sustainable options must be made more affordable, more available and more acceptable.

Believed cities should be designed around people, not machines – cited the importance of reducing car usage, facilitating more effective public consultation with young people to design future cities, and encouraging more eco-friendly design.

- © Fairfax NZ News