Scotland needs to double public spending on home energy efficiency to £250 million a year if it is to meet climate crisis targets.

That is the conclusion of the World Wildlife Fund (WWF) as it warns the country is moving too slowly to wean itself from planet-destroying gas boilers.

The campaign group reckons Scotland needs to double its current level of energy efficiency updates to 80,000 a year.

Heating accounts for half of Scotland’s energy use – and most of that is powered by fossil fuels.

A spokesperson for WWF Scotland said: “If current rates of energy efficiency and clean heating are not improved, Scotland will either be stuck burning large amounts of damaging fossil fuels in 2045, or will risk a disruptive, rushed and costly exercise to rapidly retrofit clean heating systems in the 2030s.”

The group hired Vivid Economics to calculate how much work needs to get done for Scotland to achieve zero-net carbon by 2045. The economists worked out that, on average, 70,000 homes per year will need to have a renewable heating system installed annually between now and 2050. That compares with between 1,000 and 2,000 homes per year currently.

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The WWF research echoes work done for ScottishPower, which said that some £16 billion will have to be spent by 2045 replacing two million gas boilers with electric heat pumps.

Householders, of course, would most likely be replacing their boilers in that period anyway. However, some economists believe climate pressure could mean just allowing people to replace gas boilers when they die will not achieve a fast enough switch.

ScottishPower said that extra car-charging points and boilers – and extra capacity to power them – would mean investment, from all sources, of £25bn in total.

WWF Scotland is suggesting state backing for a new Scottish renewable heat-pump grant to help businesses, landlords and householders switch away from gas.

Robin Parker, climate and energy policy manager at WWF Scotland, said: “Fossil fuel heating is a major cause of climate pollution in Scotland, and it’s the next big frontier for reducing emissions, that we need to address properly if we are to play our full part in responding to the climate emergency.

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“While there is some scope for individuals to ensure that their homes are not wasting heat, most of this change needs to be led by government, working with local authorities. When it comes to replacing a boiler, unlike buying a new car, the consumer is in the hands of the installer, so government financial support and regulation are the main way we can make a difference.

“We have all the technological answers we need, there are already thousands of Scots enjoying warm, renewably heated homes, free from fossil fuels. That’s something we should all be able to enjoy, just as it is already the norm in many other northern European countries. By investing in cosy, green homes, the Scottish Government can respond to the climate emergency, protect fuel poor and vulnerable households, and create a new renewable heating industry in Scotland.”

Maarten Hage, senior economist at Vivid Economics, said: “This new report translates the new net-zero 2045 target into the implications for the scale and pace of change required. For example, heat pumps will need to be installed at a far greater rate than the current installation rate of gas boilers.

“We are beyond the point of fitting in with existing replacement cycles of heating equipment, and delay will increase costs. Scotland is well placed to make this transition, and by learning lessons from overseas, such as capital cost subsidies and involvement of local authorities, the transition is achievable”

Only 9,000 heat pumps have been fitted in Scotland since 2014.