It has taken a while but I think I have finally found it,
"Tom came back out of the cave, his face muddy but happy. He came over and sat down near the Chief Fireman. Looking into his eyes, Tom asked:
“So, human beings are responsible for climate change?”
The Chief Fireman was silent for a moment.
Then he said:
“Yes, Tom, the greenhouse gases come from our cars, our planes, our factories, even our fire-engines; so we all have to take our share of the responsibility”.
“Oh” said Tom, who was thinking hard. “Right. So... What can I do to stop these gases getting into the atmosphere and warming up the earth?”
“What you can do, Tom, is ask your Mum or Dad not to use the car so often. Instead of going to work or school by car every day you could walk, or take public transport, or go by bike”."
Then big government lends a hand,
“I tell you what” said Tom: “Why not give medals to everyone who rides their bike every day, and everyone who uses energy from the wind and the sun, and everyone who leaves their car at home and takes the bus instead... Give medals to everyone who tries to stop producing greenhouse gases! Those people are the real heroes!”
The Mayor smiled at Tom.
“That is a great idea!” he said. “I will do something about it straight away!”