IF ALL Sydney's car commuters stopped their vehicles two kilometres away from work today, got out and walked the rest of the way, the city would be spared 1200 tonnes of carbon emissions.

If they did the same thing every working day for a year, the reduction would be 312,000 tonnes.

It may be naive to think 1.2 million Sydneysiders would ditch their cars for climate change, but thousands will begin that journey with a single step today.