The Greens have offered the government their necessary support for its signature climate change legislation, with a single condition that new coal and gas projects are blocked from development.

The government will introduce its "safeguard mechanism" bill to the parliament this week, which would require the nation's top polluting facilities to reduce their emissions by 4.9 per cent each year to 2030, or face penalties.

The mechanism is the core of the government's plan to reduce emissions by 43 per cent by the decade's end.

The Greens say that is a weak target, and hold concerns that the safeguard mechanism would allow facilities to buy offsets to cover their obligations instead of cutting emissions.

But Greens leader Adam Bandt says the party is willing to put aside those concerns if the government will accept a single amendment to block new coal and gas projects.

"We're prepared to live with those and give Labor's scheme a go if Labor is prepared to stop opening coal and gas mines," Mr Bandt said.

"The Coalition has said no, that they're not interested, that means the government needs the Greens to get this through parliament.

More than 100 gas and coal projects would be blocked under proposal

The Department of Industry, Resources and Energy has recorded more than 100 coal and gas projects either in development or being considered with commercial start dates before 2030.

Some of those projects are small expansions but others such as the Scarborough and Browse gas developments would become among the biggest in the country.

Mr Bandt says the government's 43 per cent emissions target would be "beyond reach" if those projects proceeded.