World Vision Australia has criticised the country's policy makers for 'waiting too long' to reduce carbon emissions.

Although urged by state governments, Prime Minister John Howard has refused to set a target for carbon emissions.

Speaking at a climate change conference in Brisbane, World Vision Australia CEO Tim Costello says Australia must work with other countries to reduce emissions.

"We have to move beyond saying, 'well if someone else doesn't do something, why should we? If someone else hasn't set a target then we shouldn't,'" he said.

"We cannot see climate change just stopping at our borders because we say, 'well it's really China and India who are contributing the most.'"

The Commonwealth Scientific and Industrial Research Organisation warned in February that if climate change goes unchecked in Sydney by the year 2070, the city is in threat of severe droughts nine out of every 10 years, a dramatic rise in the number of bush fires, and freak storm surges which could devastate the coastline.

If residents do not cut water consumption by more than 50 per cent in the city over the next 20 years, the city will become unsustainable.

The report also warned that temperatures could rise 5C above the predicted global average, which would leave the city facing an almost permanent state of drought.