Dr Jane Goodall – the world's foremost expert on chimpanzees – says the essential starting point for positive change is each of us thinking about the consequences of the small choices we make each day.
While the current state of the environment is "very, very bad", Goodall believes we still have a window of time to fight climate change.
Her hope lies mostly in the young.
"Once they understand the problems and they're empowered to take action I am so impressed by their energy, their enthusiasm, sometimes their courage."
Goodall says the main reason she is still working is the youth programme Jane Goodall's Roots & Shoots, which began in 1991.
If we all commit to considering the consequences of what we choose to buy, eat and wear, hope for the planet is transformed into action, she says.
"Where does it come from? How was it made? Did it harm the environment? Did it result in cruelty to animals or child slave labour in a far-off place - is that why it's cheap? Could you buy something else? Do you really need it?
"If everybody starts making ethical decisions, then we move towards a better world."