Want to save the planet? Start by turning out the light

Unusual heat waves and floods will become more common as global warming advances, but everyone has the power to turn back its effects, a leading international climate scientist says.

Professor Will Steffen said the world was facing a potentially dire future, but turning back the tide could start in suburbia.

"When you look at greenhouse gas emissions, it's made up of an enormous number of decisions day in and day out by a huge number of people.

"There are a lot of little things you can do. You can turn off the lights when you're not using them." Doing so would save significant power, he said.

Professor Steffen, in New Zealand for the International Science Festival in Dunedin, said changes that are planet-friendly do not necessarily mean a lifestyle compromise.

Based at Canberra's Australian National University, where he heads the Centre for Resource and Environmental Studies, Professor Steffen and his family moved from the suburbs to the city centre to compensate for the city's poor public transport system.

"[It] means two things, one I can walk to university, and my wife, who's a public servant, can walk to her office. Neither of us use motorcars. Our daughter can use the bus to get to university.

"We have just as good a lifestyle, and we're closer to restaurants, cafes and theatres. We don't think our lifestyle has suffered, in fact we think it's improved, and we've cut down on gas emissions."

The evidence is showing that climactic changes have gone beyond the realms of natural variability, he said.

"What we see now in the second half of the 20th century is unusual. It can't be explained by any known mode of natural variability."

But debate still rages about how much and how rapid climate change will occur this century. Professor Steffen believes that over the next 20 years, heat waves and floods will become more frequent, but the jury is still out on whether more intense cyclones can be expected.

The most vulnerable will be those along the coastline, where sea levels have risen 20cm in the past 50 years.

"Doesn't sound like very much, but it is important for low-lying Pacific Islands. And the projections are that our best guess for this century is another 50cm ... by the end of the century."

The issue long term will be the stability of the ice sheets. If temperatures rise beyond two-to-three degrees, sea levels can be expected to rise 5m, as they did during the earth's previous warm period, he said.

But the planet's doom is not inevitable. "If we cause it, we can stop causing it. It requires global change in the way we think about our role in the planet.

"I want us to get away from the debate where if we don't have these intense fossil fuel energy systems, we're going to go backwards.

"We have to get over that debate. Let's think of alternative futures that are attractive, that people want to live and they would enjoy living in, and yet, vastly reduce the amount of these gases. I think we can do it."