It takes into account use of appliances, diet, travel and consumer habits, and calculates roughly how much nature we need to sustain our lifestyles. According to the Environment Protection Authority task force that reviewed my case, eating habits are the largest contributor to an ecological footprint. About 60 per cent of my foodstuffs are organic, but 40 per cent is still processed and packaged and often imported or from interstate.

I eat meat and fish about five times a week, which is a no-no. Meat eaters might consider how many more forests are cleared to make room for cows and sheep that erode the land through grazing. For those buying supermarket vegetables, consider the trucks or planes used to transport them, the chemicals and refrigerators used to preserve them and the exhausted soils that grow them. For every human need, there is an environmental impact.

The disconcerting news is that humanity's average footprint is 2.3 hectares per person, but only 1.9 hectares per person are available. The planet is way over quota. The world's wealthiest nations are consuming non-renewable resources and depleting global reserves at a faster rate than ever before. We are mortgaging the future at the expense of our children, the poor and the long-term health of our planet, according to the latest reports.

California-based Redefining Progress is a non-profit organisation working with world partners to shift public policy and economies toward sustainability. Its latest report, The Ecological Footprint of Nations 2004, brands America as the worst offender, with the world's largest footprint of 9.57 hectares per person. Australia sits at number eight on the top-10 table of resource-guzzling countries.

Sustainability requires living within the regenerative and absorptive capacity of the planet The liquidation of our ecological assets is called overshoot and is not sustainable, the report says.

Right now, humanity's combined footprint is overshooting the Earth's natural resources by 15 per cent.

Unless we change our greedy habits, we may be faced with permanent energy rationing, something like the food rationing that occurred during World War II.

In his book, How We Can Save the Planet, co-authored with Tina Fawcett, Dr Mayer Hillman, a senior fellow emeritus at the Policy Studies Institute in London, outlines how a system of personal carbon rationing might work. It would be a mandatory system, he says, established by governments, with equal rations for adults and appropriate rations for children, yearly reductions of rations as we deplete resources, and the possibility of tradeable rations, so an individual might swap an overseas trip in exchange for less household energy.

It is possible to dramatically reduce a nation's footprint, however, by seriously addressing the ecological impact of its fossil fuels usage and shifting to renewable energy sources, the report says.

About one-fifth of Australia's total greenhouse gas emissions come from households. Seven million Australian homes produce more than 15 million tonnes of greenhouse gas emissions every year electrical appliances account for 52 per cent, heating and cooling account for 15 per cent, water heaters are responsible for 28 per cent, while cooking covers for 5 per cent.

Victorian families are huge energy wasters, according to a study by Environment Victoria, casually throwing away an average $570 extra each year on power and water bills. Washing clothes in hot water uses $75 more than if we washed them in cold. Too lazy to turn off the TV or stereo, we pay an extra $60 a year for remote-ready standby power. You could save 20 to 30 litres of water each shower by using a AAA-rated, water-efficient shower head. An electric kettle or gas cooker generates about one kilogram of greenhouse gas for every 10 litres of water boiled, compared to half as much if you used a microwave or electric cook top.

A 20-watt compact fluorescent globe runs for about five years and will save about $80 and 650kg of greenhouse gas in that time. Every litre of petrol saved reduces gas emissions from cars by 2.9kg, but you could save 100kg of emissions each year if you converted your car to LPG. There are oodles of tips on how to conserve energy and avoid emissions.