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When her first electricity bill arrived, Hollie Osborne's dream of a "forever home" for herself and her two-year-old son began to disintegrate.
She had been delighted to receive a flat, just a few doors down from her mother, in a new social housing development built in a handsome red-brick former school in Glasgow.
The home represented a chance for the single mother to rebuild her life, after a period of struggling with serious mental-health issues.
But as the harsh Scottish winter set in, she found the flat's heating needed to be on constantly to stay warm - and the 150-pound ($200) monthly bills that began arriving represented half her income.
"I was having to bring my boy in bed beside me, just because I couldn't afford to put the heating on," Osborne said.
"It's meant to be my forever home with my child - and I can't afford to live here now."
A spokesperson for the Home Group Scotland housing association that owns and manages the property said it was working to resolve issues with heating in some flats and was offering support to tenants who had received high bills.
Several miles up the road, Tizo Seleman, 40, and his partner Saada Mwalimu, both care workers who live with their baby daughter in a high-rise block in Glasgow's northern Springburn district, expect their once-onerous heating bills to shrink.
In July, their inefficient old heaters were replaced with a low-carbon air-source heat pump system - part of a bid by their social housing landlord to both make heat cheaper for tenants and slash climate-changing emissions.
"I think it will make a real difference – I will get some savings," predicted Seleman, who said he looks forward to less scrimping on daily costs and maybe even putting some money aside for a holiday abroad with his family.
In cities around the world, making existing homes more energy efficient and switching them to run on green power is a huge challenge as the world tries to swiftly slash climate-changing emissions.
Glasgow, a former industrial hub that will host the key COP26 U.N. climate negotiations this November, is one of those trying to drive the shift as part of the C40 Cities network, a global group of nearly 100 major cities working for faster action on climate change.
The cities have each committed to delivering climate action plans designed to spur uptake of clean energy, boost adaptation to climate threats and turn the 2015 Paris Agreement on climate change into an on-the-ground reality.
Under its push, Glasgow - which has pledged to reach net-zero emissions by 2030 - has focused on about 60 actions that include pulling water-source heat from the city's River Clyde, improving public transport and planting more urban trees.
One key policy focus has been finding ways to make its homes climate-smart, comfortable and cheaper to heat while ensuring those least able to afford the green shift are not left out.
That is not an easy job in a port city noted for its winter cold, where budgets are limited and restrictions on how historic homes can be modified make retrofits challenging.
"If people are left behind, then it's not going to tackle emissions," said James Roberts of Living Rent, a renters' union which works with low- and middle-income people.
About 15% of Scotland's climate-changing emissions come from heating homes, which makes finding low-carbon ways to keep families warm a priority as Britain aims to slash its emissions by a hefty 78% by 2035.
But in Glasgow, where around a quarter of the population is thought to live in fuel poverty - meaning heating bills eat up more than 10% of their income - ensuring green heat is affordable is also crucial.
"It is one of our biggest climate justice issues," said Susan Aitken, leader of the Glasgow City Council.
She said the council wants to make sure efforts to decarbonise also speed up "the way in which we are addressing some of these long-standing social and economic inequalities".
"We need to make sure every single pound that we invest in the city is delivering multiple benefits," she told the Thomson Reuters Foundation.
While Glasgow looks to the future, its streets remain largely shaped by its past.
The city is known for its sweeping terraces of red and blonde sandstone tenements – properties built in the late 19th and early 20th centuries that contain multiple flats and make up about 20% of Glasgow's homes, according to the council.
While beloved for their high ceilings, original fireplaces and other features, the tenements are also considered chilly and sometimes damp, while their stonework and historic features make efficiency upgrades more challenging.
But one project in the inner city aims to blueprint how to revamp them to the highest modern energy-efficiency standards without losing their unique character.
An eight-flat tenement in Glasgow's southern Govanhill district has been stripped back to its bare bones for a deep retrofit from its foundations to its roof.
The work includes new insulation for walls, floors and the roof, plus triple-glazed windows and air-source heat pumps.
"This is the first of its kind. That's why it's exciting - but it's also challenging," said Drew Carr from John Gilbert Architects, which is leading the work for the Southside Housing Association.
"You can't just focus on the energy (improvements). You've got to have heritage," he said.
Some compromises have had to be made. The sandstone on the back and side of the building is being covered up with a high-efficiency external cladding to help keep in heat, though the front has been preserved.
The retrofit aims to reduce energy bills for homeowners by up to 90%. How the building functions will be monitored by researchers, with data used to inform future tenement upgrades.
"There are about 180,000 tenements in Scotland, so if this one goes well, it works and the tenants love it, we've got a lot of work to do," said Carr.
Social housing organisations, which provide affordable rented homes mainly for low-wage or vulnerable tenants, are among those leading projects to improve building energy efficiency as they face tightening government regulations.
In the high-rise blocks in Springburn where Seleman lives, a 2016 survey of tenants by housing association ng homes found more than 60% were living in fuel poverty.
Some, desperate for heat, were caught smuggling in bottles of cooking gas, risking fires to try to warm their homes.
Resident Margaret Galloway, 77, said that despite her efforts to turn off radiators and limit her energy use, her last annual electricity bill came to 1,345 pounds ($1,850).
"Sometimes I wouldn't maybe eat, and just have an egg or something at teatime instead of cooking anything" on her electric stove, she said.
Her association is now ripping out old, inefficient electric heaters and replacing them with a low-carbon "district heating" system where heat from a bank of air-source heat pumps on the roof is shared among flats.
"That benefits folk because it's real money back in your hands," said John Thorburn, chair of the board at ng homes.
"That is how you improve someone's life - you give them more choices because they've got some extra cash."
In Glasgow's city centre, meanwhile, three 1960s housing blocks owned by Queens Cross Housing Association and originally slated for demolition have been transformed with new insulation, ventilation and community spaces for residents.
Finished in a striking modern white, grey and gold design, they now look like new-built homes, with an energy rating to match.
Such major projects are not cheap. The total bill to revamp the three blocks was about 15 million pounds ($20.7 million), including about 22,000 pounds ($30,000) per flat on energy efficiency improvements.
Such costs can put major upgrades out of reach for many private homeowners. The Scottish Federation of Housing Associations also found its members need more help with funding to meet new efficiency targets.
But other measures could also drive needed shifts, including legislation, incentives and more work to join up "piecemeal" funding for improvements, said Rupert Daly of Collective Architecture, which led the work on the Queens Cross blocks.
"If you can do something once and not have to invest in subsequent upgrades because you've done it right initially - there's value in that," he said.
As Glasgow looks for new green energy sources, it is turning in part to the wide Clyde River that winds through its centre.
"When you look at the areas of highest heat demand, they all really follow the river," said John Maslen, of social enterprise Greenspace Scotland.
That organisation's ParkPower project explores how urban green spaces and water could help provide low-carbon energy.
The Clyde's waters may seem chilly but heat stored in the river could be used to meet half the city's total heating demand, the group estimates.
In much the same way as air-source heat devices work, large water-source heat pumps could draw residual heat from the Clyde. That could then be piped to homes and businesses, providing a lower-carbon alternative to traditional heating systems.
The Clyde's heat is already fuelling one district heat network serving homes and businesses just outside Glasgow, and another planned system will power a high-tech 'innovation district' in the city centre.
The two projects barely scratch the surface of the Clyde's potential, said Maslen, who noted the systems could also provide summer cooling as climate change brings more extreme heat to a city long worried mainly about staving off cold.
While river-sourced green heating offers the potential for big emissions cuts, Glasgow is also trying out smaller-scale community energy projects.
Glasgow Community Energy, for instance, aims to share profits from renewable power installations with local people, while building awareness about climate change and the benefits of acting on it.
The co-operative last year installed solar panels on two schools in less-well-off areas of the city, partially funded by people living nearby who invested their own cash in the project.
The group sells energy from the panels to the council to power the schools, with any excess going to the national grid.
Shareholders - who get their investment stake back as the panels pay for themselves - can then vote on where to reinvest any additional profits in their community.
"You're generating energy here that brings income to people here," board member Fraser Stewart told the Thomson Reuters Foundation.
Stewart said the effort launched deliberately in less-wealthy districts, with organisers keen to make clean energy innovations – and the income they generate - available to poorer areas more likely to struggle with the high upfront costs of installing solar and other renewable technology.
The co-op expects to take in between 5,000 and 10,000 pounds ($7,000-$14,000) a year from each of its two solar installations, Stewart said.
Early ideas for using the money include improving youth sports facilities and installing street flower planters.
The co-operative also runs education sessions to help local school students and residents learn more about climate change and renewables. It plans to expand the clean power installation push to new school districts and communities, he said.
With the climate "emergency" and solutions to tackle it affecting everyone, there is a need "to get as many of those people around the table as you can, and have those voices heard properly", Stewart said.
One catch in getting low-carbon heat into Glasgow homes is that although renewable systems can compete on price with heat produced from fossil-fuel electricity, the gas boilers that still warm the vast majority of homes remain even cheaper.
"The challenge is currently what they call the 'spark gap', which is the difference in price between gas and everything else," said Maslen, of Greenspace Scotland.
Largely thanks to growing supplies as a result of fracking, fossil-fuel gas costs about 3 pence per kilowatt-hour (kWh) compared to an average of about 17 pence for electricity, he said.
Ensuring that a switch away from gas to meet climate change goals does not increase fuel poverty might require a major subsidy scheme for poorer households, Maslen said.
But with Glasgow accounting for 20% of Scotland's heating demand, investing in a switch to greener heat in the city could push Scotland much closer to its emissions-cutting goals, backers said.
City officials said they are now looking at larger-scale projects to draw heat from the Clyde, which would cost hundreds of millions of pounds.
Aitken, Glasgow's council leader, acknowledged there is a "big question" about the cost of renewables compared to gas, and said the city is exploring its options.
National governments need to look at adjusting regulations and subsidies around all fuels to drive climate action, she added.
As world leaders prepare to gather at the COP26 talks in Glasgow to hammer out rules designed to drive swifter and larger reductions in planet-heating emissions, one of the most crucial questions will be how to finance it all.
"The huge issue with a 'just transition' and retrofitting is who's going to pay?" said Michael Mikulewicz, a research fellow at the Centre for Climate Justice at Glasgow Caledonian University.
Glasgow City Council leader Aitken said reaching the city's aim of net-zero emissions by 2030 is likely to require about 30 billion pounds ($41 billion) of investment, including 5 billion pounds just to retrofit homes in the city to higher efficiency standards.
"Governments alone can't deliver this. We need to have private investment come in," she said.
Officials are looking to court major investors and are working with groups such as Bloomberg Philanthropies and the World Economic Forum to develop projects that could attract significant private cash.
The city will launch an investment prospectus around the time of the COP26 conference, laying out 10 major projects.
Aitken said many big lenders see existing city projects as too small to be worth their time - and the answer may be to group the initiatives or offer opportunities spanning multiple cities or wider regions.
To drive investment, governments must step in to make regulations clear and help underwrite risks to investors - such as by agreeing to buy the clean energy produced, she said.
Glasgow will work to make the voices of city leaders heard at the COP26 climate talks, Aitken said, calling cities crucial players in the race to reach net-zero goals.
"Cities are where most of the emissions are generated because it's where most of the people are - but it's also where you get the biggest gains in decarbonisation most quickly," she said.
Roberts, of the Living Rent union, said the coming green shifts had to work for people - including the poorest - as well as the climate.
"Either we all move together as a society on this, or it all becomes sound-bites and just hot air," he said.
Reporting: Sonia Elks
Text editing: Laurie Goering and Megan Rowling
Photographer: Dan Phillips
Producer: Amber Milne
Additional reporting: Amber Milne
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