Slicing the Apple I would like to start by asking you to do a little visualisation exercise with me. Imagine the Earth as an apple.

Now, imagine you have a sharp knife, and carefully cut the apple into four pieces. Put three of these pieces to one side, as they represent the Earth's oceans - places where humans cannot live. Put three of these pieces to one side, as they represent the Earth's oceans - places where humans cannot live.

Take the remaining quarter of your apple (which represents the land area of Earth). Cut it in half and put one half aside. This portion represents the poles, the deserts, the lakes, the rivers and the high mountains, where humans cannot live for more than brief periods.

Now take the remaining one eighth or your apple and cut it into four pieces. Now take the remaining one eighth or your apple and cut it into four pieces. ► Put three of these aside, as they represent the places where humans live but where we don't grow food ► places which are too hot, too cold, too dry, too wet, too steep or too barren to grow food. ► Plus, of course, those places where we could grow food, but which we have covered over - places like cities, towns, villages, roads, golf courses, motorways and cultural icons such as McDonald's carparks.

Take the remaining 1/32nd of your apple and, being careful not to cut yourself with your imaginary knife, peel the skin off and hold it in the bowl of your cupped hands. This tiny sliver represents the places in the world where we can and do grow food - where the soil is fertile and the atmosphere provides clean air and fresh water. Treat it as if your life depends on it.  - Because it does.

Now comes the tricky bit. Very carefully cut off 1/500th of this sliver and imagine this as the parts of NZ where we can and do grow food (roughly 0.18 % of the earth's land surface). Not only are we utterly dependent on this speck of soil about 1.5 metres thick, and the atmosphere above it, we are also utterly responsible for it. You would think that our prime priority as inhabitants of this land would be to protect the source of all our health and wellbeing.