From a science-packed work on the world's booming population to a quiet meditation on a beloved landscape, British director Katie Mitchell is on a green crusade at this month's Avignon festival.

Created for the theatre gathering in southern France together with the scientist Stephen Emmott, "Ten Billion" is billed as a new kind of lecture, about the danger a mushrooming population poses for the planet.

"It's just so sad," Mitchell told AFP of her research for the work, which premieres in Avignon on July 23 before heading to London to be performed during the Olympics.

"I wanted to make this show because I didn't want my child in 20 or 30 years to say to me, 'Did you know that there was a very high possibility of these things happening?" she explained.

"I wanted to be able to say to her, 'I knew and I tried to do something very small only in my own field'

"Because I don't want their generation to waste their energy being angry with us for doing nothing -- I think they will have enough to cope with in the future without rage at our generation."

Part one of the play looks at human activity since around 1800 and the problems it has caused, whether land use, water, transport, industrial energy, carbon use, or climate change.

Section two looks at what is being done right now, and how the planet's many environmental challenges are tightly interlinked.

"The third part asks what are the possible futures we face and what are our choices -- and then what this scientist thinks," Mitchell said. "He is very measured, very calm, objective and without sensation."

Mitchell's family went back to live on the land in the 1970s and she grew up in the countryside, but she cites her meeting with Emmott three years ago as a turning point in terms of environmental awareness.

--'Quiet, contemplative, gentle' --

Professor of computational science at Oxford University, he also heads a Microsoft laboratory that focuses on modelling natural systems, for instance to predict the future of the climate or life on Earth.

"The process has been to get him to translate his ideas into simple concrete sentences and points that we can actually understand -- but without simplifying the reality," Mitchell explained.

The second play she is bringing to Avignon is inspired by "The Rings of Saturn", a novel about a walking tour of Suffolk on England's east coast by the late German writer W.G. Sebald.

"I love the landscape he is writing about, it is one of my favourite places," she said.

But adapting the Sebald -- in its original form a solitary mediation, utterly "untheatrical" -- for the stage, was also a sizeable challenge.

"It's very hard to make a man walking and thinking into a live performance -- its such a delicate thing."

Mitchell enrolled three actors to play out the narrator's thoughts, and five performers to recreate the sounds and textures of the land -- the crunch of gravel, the brush of undergrowth, twigs breaking, the rumble of the waves.

"The event is a very quiet, contemplative, gentle evening," she said of the play, which premiered on Sunday in German with subtitles.

"I suppose the Sebald and 'Ten billion' have a conversation," she mused.

"One is about a walk along a landscape that is very beautiful but will disappear -- it's a celebration of a bit of coastland that is vulnerable."

"And the other show is about the facts of what could happen in the future, and what human beings have done to the planet."

This year's Avignon festival has a strong British flavour with actor-director Simon McBurney as guest artist and British works looming large among the 36 to be performed in the official programme until July 28.