This article appears as part of the Unspun: Scottish Politics newsletter.

Despite all the alarm and scare stories about heat pumps, the Scottish Government is pressing ahead with legislation to legally require people to rip out gas boilers – and the SNP will need to take responsibility if the strategy has any chance of being successful.

A lot has been said about heat pumps in the two years since Patrick Harvie first touted his heat-in-buildings strategy.

We’ve heard that they won’t work in Scotland because it’s too cold, we’ve heard they are too noisy – both of these claims have been found to be utter mince.

Not a great deal has changed since Mr Harvie set out his original plan – the timescales, from 2028, for people to start being required to do the work, remain pretty much identical.

But the launch of a consultation on his draft plans coming two years on from that original floating of intentions raises questions, given that time to do this is running out.

No-one will be required to do anything by 2028, and for clarity, this doesn’t mean people will necessarily need to replace their boiler with a heat pump by then.

Instead, landlords and home-owners will be required to meet modernised energy efficiency standards first – which will take the heating system such as a boiler or heat pump into account, as well as the fabric of the building and other efficiency measures.

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By 2045, all homes will be required to make the switch to heat pumps or other renewable heating systems – with people who buy a new property before then asked to meet the standards sooner after grace periods.

One thing that has changed since Mr Harvie first set out his plan in 2021 is a bold pledge he made that one million homes in Scotland will be decarbonised by 2030.

But that ambition has been torn up, with Mr Harvie admitting that the “scale of change is not achievable by that date”.

The Greens co-leader claimed that his watering down of his pledge “allows us to gain the full benefit of the technological innovation that is already taking place”.

That might well be true, but Scotland had an almost impossible climate target to be met by 2030. That ambition has been pushed more out of reach by the move.

Scotland has cut around 50% of 1990 levels of emissions so far.

But by 2030 that progress will need to reach 75%, a target the Climate Change Committee has warned looks like it is sliding out of view.

Heat in buildings makes up around 13% of Scotland’s emissions, so work will need to speed up, not slow down.

That 2030 target to decarbonise one million homes was also important because Scotland’s largest two cities, Glasgow and Edinburgh, have pledged to become net zero by then.

City leaders remain adamant these targets remain on track, but the biggest challenge will be decarbonising heating systems for homes.

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And that brings us to the elephant in the room, which has been sat there patiently since 2021.

How on earth are we going to afford all this?

Back in 2021, Mr Harvie bluntly said that the total estimated cost for transforming our buildings into ones that do not burn fossil fuels to heat them is a whopping £33 billion.

That was before costs shot up in the current economic climate and the fallout from the Covid pandemic, so they could, in reality, be even higher.

Mr Harvie’s government has pledged £1.8 billion towards this and the Scottish Government has been open that the bulk of the costs will come from the private sector, not public funds.

But this pivotal part of the plan is still missing.

The Herald: Back in 2021, the cost to transform buildings to clean fuels was estimated at £33bnBack in 2021, the cost to transform buildings to clean fuels was estimated at £33bn (Image: Newsquest)
Efforts were made by former first minister Nicola Sturgeon to lobby investors in the City of London to part with money to fund Scotland’s green transition, but that strategy has yet to produce anything concrete.

The Scottish Government does offer the most generous grants of any part of the UK – around £7,500 for insulation improvements and an additional £7,500 for heating systems.

But as it stands, without the hoped private investment hoped for, people will have to pay to upgrade their homes in the coming years.

The political fallout for Mr Harvie hinges on the costs of this plan.

It is difficult to fault the ambition despite the worrying rowing back of the pledge to decarbonise one million homes by 2030.

But the confidence for both homeowners and businesses will come from a proper funding plan.

Mr Harvie could do with some friendly faces from his partners in government, the SNP, to back him up in this enormous task at hand.

But only a handful of SNP MSPs bothered to turn up in the Holyrood chamber as he launched his crucial consultation. Net Zero Secretary Mairi McAllan was the only cabinet secretary in attendance.

SNP backbenchers asked questions including about hydrogen and problems with the electricity grid capacity – largely distractions at this stage when heat pumps are being pushed ahead with.

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Kenny Gibson, sat directly behind Mr Harvie, asked him an awkward question about homes that cannot be retrofitted and my story about grants and loans for solar panels only now being available if people also fork out for a new heating system like a heat pump.

Mr Harvie has one of the most difficult jobs in government. But without solutions to remaining unanswered questions, and large parts of the SNP failing to take ownership of one of its government’s key policies, much like the deposit return scheme, Scotland risks falling short of a crucial part of tackling the climate crisis.