THE Baillieu government is under pressure to explain how it will deliver a 20 per cent cut in greenhouse gas emissions after Victoria quietly adopted Australia's most ambitious climate change legislation without introducing new policies to meet it.

The Climate Change Act - introduced by the former Brumby Labor government and passed last year with bipartisan support - came into effect yesterday.

It requires the government to cut the state's emissions by a fifth by 2020 and empowers the Environment Protection Authority to regulate emissions from industry.

Critics said the government had no clear plan to deliver what the act demanded.

Premier Ted Baillieu has described the 2020 greenhouse target as ''aspirational''.

Environment Victoria accused the government of removing last year's climate change white paper - which set out the basis for the act - from its websites in recent days. It responded by posting the paper on its own website. ''It seems the state government is deliberately creating a climate change policy vacuum,'' Environment Victoria campaigns director Mark Wakeham said.

Michael Power, a lawyer with the Environment Defenders Office, said the act defined greenhouse gases as ''waste'' and set up the EPA to regulate emissions from large industry and brown-coal electricity plants. But he said the government would first be expected to write policy and regulations setting out in detail how the powers could be used.

''So far the government has done nothing, which in itself is indication they are not planning to use it,'' Mr Power said.

A government spokeswoman said it would make an informed decision about the Climate Change Act after the federal government introduced carbon tax legislation.

But she said the state government had started working on fulfilling responsibilities under the act, including developing a climate change adaptation plan and a report on Victorian emissions data.

She said the government had doubled an energy saver scheme so that it would cut 5.4 million tonnes of emissions a year and allocated more than $200 million to climate programs in the recent budget.

Opposition climate change spokeswoman Lisa Neville said the government had no climate plan and its budget initiatives paid only lip service to reducing emissions.

''One of the first things Mr Baillieu did as Premier was tear up Labor's staged shutdown of the dirty Hazelwood power station, and Mr Baillieu has since supported [coal technology company] HRL's bid to build a new coal-fire power station,'' she said.