Three teams of scientists have worked out how to cut the cost of home insulation, how to cool tomorrow’s ever-hotter cities, and how to reduce household greenhouse gas emissions. And the potential solutions are, in every sense, green.

Researchers in the UK report that they could limit heat lost through the walls of a building—on their own university campus—by planting a vertical garden all the way up the façade.

Scientists in Switzerland looked at land surface temperatures from 293 cities on the European continent to confirm, in the journal Nature Communications, that the coolest urban spaces were those covered by trees.

And a second group of British researchers reports that rather than addressing fossil fuel consumption with carbon taxes, the fairest approach would be to make electricity from renewable energy sources available for nothing—and offer free public transport, as well. “It’s redistributive, saves emissions, and reduces fuel and transport poverty,” said lead author Milena Buchs of the University of Leeds.

Findings of this kind have to be tested thoroughly before they can usefully be deployed on any scale. But they offer new approaches to an accelerating challenge. Within a few decades, the proportion of the global population crowded into cities is likely to rise to two-thirds. And the fact that city-dwellers can expect to get hotter—dangerously and perhaps lethally hot—is a given, and recognized once again by a new handbook from the United Nations Environment Programme.

It warns that by mid-century, the number of people exposed to summertime highs of 35°C or more could increase eight-fold, to 1.6 billion. Demand for air conditioning—itself a source of yet more energy consumption and emissions—is likely to rise threefold, but this is not a solution available to the poorest, and most vulnerable.

Nature, however, might once again have part of the answer. In Britain, buildings account for 17% of all greenhouse gas emissions, and 60% of all the energy used inside those buildings is to keep them warm. An estimated 57% of the structures were put up before 1964, when thermal standards for new buildings changed, so the older buildings are a substantial part of the problem.

The Sustainability Hub at the University of Plymouth in the UK faces south and west. So researchers used one of the façades for an experiment in living insulation: they covered it with a flexible fabric sheet fitted with pockets for soil and started planting sedges, rushes, and flowering shrubs. Then they measured the difference in chambers behind the green wall and the plain masonry one.

They report, in the journal Buildings and Environment, that the heat lost through the green and flowering façade was 31.4% lower than the original structure. Daytime temperatures within that part of the building remained more stable, so less energy was needed for heating.

“Living walls can offer improved air quality, noise reduction, and elevated health and well-being,” said project team member Thomas Murphy of the University of Plymouth. They could also save energy, reduce emissions and help reduce biodiversity loss.

The UK’s cities spend more on heating than cooling, but even so, Swiss scientists included 10 British cities in their survey of high-resolution satellite data of urban land surface temperatures across the entire continent, from Norway to Malta and from Ireland to Turkey. They found that, during hot extremes in most cities, urban trees were cooler than urban bricks and mortar: in the south, up to 4°C lower, and in central Europe from 8 to 12°C lower.

Open green spaces could help, but were less effective that those covered by canopy.

“The temperature differences between rural forests and continuous urban fabric closely resemble the temperature differences between urban trees and urban fabric,” they write. “In summary, our results confirm the high potential of trees to mitigate urban heat in Europe.”

In Leeds, in the north of England, a research team approached the green living problem in taxation terms: a study published in the journal Environmental Research Letters found a way to reduce home energy emissions by 13.4%, and motor fuel emissions by 23.8%. They argue that carbon taxes on home energy and motor fuel would place a greater strain on low-income households, which in any case contribute much less to climate change than high-income families. They looked at household expenditure of home energy and motor fuel from 275,614 households across 27 European nations to calculate the effectiveness of strategies that might address the unfairness.

Rather than trying to redistribute the carbon tax revenue among the population to solve the problem of regressive impacts of those taxes, they concluded that governments could simply make “green” electricity free, along with travel on the nation’s trains, buses, and trams. If governments simply redistributed the cash through tax rebates, the cuts in emissions would be small, and fuel and transport poverty might actually increase. But universal green vouchers with expanded renewable electricity generation would reduce emissions significantly.

“Governments urgently need to make climate policies fairer by finding ways that can compensate disadvantaged people,” said Buchs.