Faced with criticism from economists arguing his "direct action plan" was an inferior way to reduce greenhouse gases, he brushed off their scepticism as a reflection on them.

The years since are the best judge. When it abolished the carbon price in 2014, the government embraced spending as its main lever to reduce emissions. It has poured billions of dollars into other measures aiming to reduce greenhouse gases. In doing so, it has tried to reframe climate change policy in Australia as largely a matter of budget expenditure and government investment.

While carbon pricing lowered emissions before its repeal, the Coalition's smorgasbord of climate spending policies has had no such obvious impact on Australia's greenhouse gases. Much of the nation's fall in emissions since 2005 is unrelated to federal climate change spending. Economists say the centrepieces of the government's emissions reduction efforts are either failing to remove enough greenhouse gases, or rely on untested industries and technologies.

The Australian Conservation Foundation estimates for every $100 spent in last year's budget, 16 cents was for addressing climate change - down from 25 cents when the Coalition was elected.

The government may have to significantly lift its spending if it wants to buy its way to lower emissions.

The Coalition has had budget-neutral programs in its suite of climate change policies. Other emissions reductions projects involving large spending won't show up in the budget bottom line. One of them is Snowy Hydro 2.0, which involves an equity investment.

Among programs involving government budget spending, the Coalition has leant on its "direct action" plan - specifically, the Emissions Reduction Fund - to reduce greenhouse gases since it repealed carbon pricing.

It lets businesses compete to win tenders and get paid to undertake emission reduction projects.

After the Abbott government poured $2.55 billion into the fund, Prime Minister Scott Morrison renamed it the Climate Solutions Fund and allocated it another $2 billion in 2019.

The figure sounds large, but it involves spending of about $200 million a year between 2021 and 2030. Australian National University climate change economics professor Frank Jotzo says the spending is small, given the task of reducing emissions.

Energy and Emissions Reduction Minister Angus Taylor has called the fund a success in helping businesses reduce their greenhouse gases.

The government has committed $2.5 billion to date for 205 million tonnes of carbon emissions reduction. At an average cost of $12.32 per tonne, economists say the program has been cost effective.

Whether it will do enough to reduce emissions is another question.

Grattan Institute energy and climate change program director Tony Wood says the Climate Solutions Fund is only reducing emissions by a small percentage of what the nation has to achieve. He describes the maths: Australia has to reduce its carbon emissions by 500 million tonnes a year, every year. So far, the government has contracted for a cut of 205 million tonnes in total through the Climate Solutions Fund.

"It just beggars belief that government funding is the only way out," Mr Wood says.

Only 66 million tonnes of emissions abatement has already been delivered under the program. Climate Council economist Nicki Hutley says the fund hasn't done enough.

"You can't have the centrepiece of your policy as something that's effectively removed six weeks' worth of emissions out of the atmosphere over its entire lifetime. That doesn't make sense to me," she says.

Another criticism raised about the Climate Solutions Fund is that it pays for "anyway" projects, or cuts to greenhouse emissions that businesses would have made without the government money.

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Among other programs, the federal government is talking up its spending to help grow an Australian hydrogen industry as a new pillar of its emissions reduction efforts. It's committed $460 million for hydrogen hubs in almost every state and territory.

Professor Jotzo says once again the Commonwealth spending involved is small, given the amount of emissions the nation has to reduce. Early indications also show the money will fund projects involving fossil fuel-based hydrogen production, he says.

Comment was sought from Minister Taylor's office.

It's not impossible for governments to spend their way to reducing emissions, according to Mr Wood. But he says it would not be very efficient.

"What's going on there is the governments are having to decide on some basis what to spend money on, and that's a hard thing for an individual buyer to decide," he says.

The Climate Solutions Fund removes some of those challenges. But a better role for government would be to create a well-regulated market and let it reduce emissions, Mr Wood says. In that scenario, government spending could best support research into low emissions technology.

The turbulence of the Rudd, Gillard and Abbott years showed carbon pricing involves political challenges no major party seems willing to fathom today.

COVID-19 may point to another greenhouse gas reduction strategy for governments spending their way to net zero emissions.

Several nations - most notably Belgium, Canada and Denmark - are prioritising "green" spending in their economic stimulus and recovery programs. The Biden administration will attempt to do something similar, if its spending bills pass Congress.

The Global Recovery Observatory, tracking how governments are spending on COVID economic recovery, estimates that Australia is yet to commit so much of its spend to clean energy and lower-emissions infrastructure.

With an estimated 2 per cent of its economic recovery spending committed to green programs, there's a lot of room to move.

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