New Zealand could be in for a rough ride in the face of turbulent changes in the world, Parliamentary Commissioner for the Environment Morgan Williams has warned. Speaking in Marlborough, Dr Williams said the latest evidence showed global warming was happening, and an expanding China, changing world markets and water availability meant New Zealand could be in for a rough ride.

"The debate is over," he said. New Zealand should be future-proofing, and thinking and investing "outside the square". Dr Williams said New Zealand had to look after its natural assets and he challenged urban and rural leaders to discuss where it was going in the long term.

Global forces meant the planet was moving into a period of massive reshaping: "We are in for a rough road." Two big glaciers in Greenland had doubled their speed in the past two years, and were melting at the rate of hundreds of cubic kilometres every year.

Australian rainfall changes were also drastic as the wheat belt dried out and some farmers believed the industry had only a few years left in that region. Dr Williams said fresh water was the key to food production. China had 21 per cent of the world's population, but only 7 per cent of its fresh water.

Chinese agricultural production rated fourth behind its urban, residential and industrial demands. And more than 10 per cent of the world's grains were being grown with "fossil waters". Biofuels would also compete for priority with food, he said. "In many parts of the world it will be straight competition between food production and fuel production, which will have implications on grain processes. Dr Williams said New Zealand had great potential for improved milk and meat production. It needed to combat the "food miles" argument – a growing trend in Europe for people to eat food produced nearby.

"We need to take hold of that and turn it into a positive. Studies show the energy content of our produce is a lot lower than that produced in Europe." Dr Williams said competition among supermarket chains was destructive to the environment because it drove prices down. "No farmer in the world gets paid the true ecological cost of production. We need people to start talking about it. "People need to be saying: `Every time you buy a cheap lettuce, you are eating a piece of the planet somewhere'."

Dr Williams steps down from his position next year after 10 years.