Governments are not acting fast enough to reduce carbon emissions, a climate change rally in Melbourne has heard.

Wearing red, members of more than 60 environmental groups rallied in the city centre and marched to the Alexandra Gardens where they formed a human "sign" 140 metres long, spelling "Climate Emergency".

The demonstration followed yesterday's release of economist Ross Garnaut's draft report on climate change that warned Australia risked losing natural wonders like the Great Barrier Reef and Kakadu if it did not act now to combat global warning. The report also recommended an emissions trading scheme (ETS) should be up and running by 2010 and include petrol, without a cut in its excise.

Greens leader Bob Brown told Saturday's protesters Australia couldn't wait for other countries, including China and India, to act on climate change. "We are one of the most vulnerable nations in the world," he told the rally.

"We, in this wealthy lucky nation, must take a lead for the rest of the world to follow. "By 2050 we need a reduction in greenhouse gases by 90 per cent if not a totally carbon neutral economy." Senator Brown said Australia would see the economic benefits of moving away from a traditional economy based on fossil fuels.

"And we'll a have pride in ourselves, a smile on our face if we tackle climate change, because as (climate economist) Sir Nicholas Stern said, those countries which take the lead in transforming to an environmentally based economy will have the best economies as we move down this century."

The Tasmanian Greens opposition climate change spokesman Nick McKim said the state's premier, David Bartlett, needed to secure Tasmania as one of the first states to benefit from any proposed changes to nationwide climate policy. "Grasping this historic opportunity for our economy will require the premier to show leadership by engaging with the business community and every level of government to drive the attitudinal changes necessary," Mr McKim said.

"Tasmania can help Australia reduce its emissions by protecting forests and utilising our renewable energy expertise, and is uniquely placed to seize the business opportunities available in a low carbon economy. But federal Opposition Leader Brendan Nelson was more cautious on the importance of economic reform and climate change.

"It is important that we don't see haste, that we don't see ill-considered policies developed and implemented for Australia and what we will do is put Australia's interests first," Dr Nelson told journalists in Sydney.

"We've got to make sure that in this process of adjusting to climate change and implementing policies for which we will all have to pay, that we don't destroy the industries that are the backbone of, not only jobs, but our whole way of life.

"The most important thing that Mr Rudd's got to do is make sure that he has a realistic, practical, sustainable approach to climate change and that he's not captured by extremists within his government and within other parts of the community." Dr Nelson said the government needed to reveal if it planned to introduce further petrol increases, as a result of the draft Garnaut report.