Citizens’ assemblies will decide what action should be taken on the climate crisis, the Treasury’s ability to stymie green measures will be neutralised and the Green Investment Bank will be revived under proposals set to be key planks of the Liberal Democrats’ general election bid.

Along with sweeping reform of Whitehall, including bringing back a department of climate change, local government would be given new powers to cut emissions, there would be a moratorium on airport expansion and an end to fracking, and the UK would achieve net-zero carbon status by 2045 – five years sooner than the current government goal.

“Moving to net-zero is a complete game-changer,” Wera Hobhouse, the Lib Dem spokesperson for the environment and climate change, told the Guardian. “The whole of government and society need to understand the need to get to net-zero – everything we do needs to be seen in terms of that target.”

Under the proposals to be presented to the Lib Dem conference in Bournemouth this weekend, a new minister, who will attend cabinet, would be appointed chief secretary to the Treasury and oversee policy across departments to ensure it meets the zero-carbon pledge.

“The biggest hurdle [to climate policies] was always the Treasury,” said Hobhouse. Soon after Theresa May unveiled her zero-carbon target this summer, her chancellor, Philip Hammond, claimed it would cost too much. “Having a chief secretary to keep reminding the chancellor of the need to get to net-zero is key,” said Hobhouse.

To gain public support for urgent action on emissions, the Lib Dems would convene citizens’ assemblies across the country to debate new measures. These would include ways to ensure a massive expansion of electric vehicles and better public transport, and how to encourage new technology such as heating homes with hydrogen instead of gas. Councils would also be given greater powers over planning, for instance to promote electric vehicles, cycling and walking.

“Citizens’ assemblies would not replace politicians’ decision-making, but would inform the options,” said Hobhouse. “We need decisive action – the government is not doing anything, they are dithering.”

The Green Investment Bank, created under the coalition government, was sold off under George Osborne. Under a Lib Dem government, a replacement would be set up with public money, and have the powers to borrow money from the private sector.

Hobhouse said Brexit was getting in the way of tackling the climate emergency: “Brexit means having less money, and it is very counterproductive. We need international cooperation – climate change is a global problem.”

The Lib Dems would end the sale of diesel and petrol cars by 2030 – 10 years sooner than the Conservatives – and stop fracking. There would also be more support for onshore wind and solar, which Hobhouse said the Conservatives had “stopped in their tracks” by drastically changing incentive schemes and planning laws.

Green campaigning groups, keen that the climate crisis should not be overshadowed by Brexit as a general election looms, welcomed the Lib Dems’ focus. “Our country may be divided over Brexit, but it is not divided over the need for action on the nature and climate emergency – polling is consistently showing that concern over climate is at an all-time high and a large majority support urgent action,” said Gareth Redmond-King, head of climate change at WWF-UK.

“Now we need the climate and nature crisis prioritised at the highest level of government, and billions in new funding, to deliver on the rhetoric. We must stop things like airport expansion that make meeting net-zero even more difficult.”

Jenny Bates, a campaigner at Friends of the Earth, said: “With the government’s net-zero target currently lacking anywhere near enough policy to back it up, we’d like to see all parties thinking about what they’d do to make sure the target is actually reached. It’s no good talking about a net-zero future while pursuing a programme of roadbuilding, airport expansion and fracking.”