Efforts to preserve the Amazon rain forest are growing ever more urgent as the ecosystem’s destruction accelerates. A recent study shows that a new program combining on-the-ground monitoring with satellite data and smartphone technology could help put the brakes on Amazon deforestation (毁林) —and potentially that of forests elsewhere.

The scientists cooperated with 76 local communities, 36 of which participated in using satellite-based “early deforestation alerts” —an early-alert system on a smartphone app, to watch over the forest and to inspect forests and document damage. Over the next two years the participants were paid to work as forest monitors and received monthly alerts via the app when satellite data indicated local forest losses. Monitors investigated alerts and inspected for deforestation in the areas. They reported confirmed losses back to their communities which decided whether to deal with the affairs on their own or inform state authorities.

The researchers analyzed the same forest-loss satellite data from the given time period in all 76 communities. They found the program reduced forest loss by 8.4 hectares (公顷) in the first year—a 52 percent reduction compared with the average loss in the control communities, says Tara Slough, an economist at New York University. “This reduction in deforestation was concentrated in communities facing the largest threat of forest loss,” she adds.

Results for the program were less striking in its second year when forest loss was reduced by only 3.3 hectares compared with that in control communities. The researchers explain that a Peruvian government campaign against coca planting that year may have discouraged deforestation in both experimental and control communities narrowing differences between the two groups in the program.

Experts say this approach to dealing with Amazonian deforestation looks promising. Local groups may continue the work they started in the program. “We want to apply this in other communities. In doing so we are making a contribution to the world,” wrote Francisco, a community member involved in the research.

At Cleveland Bridge, in Bath, a long line of traffic is building up. Although the Georgian structure was praised for its handsome Greek Revival style by Nikolaus Pevsner, an architectural master, it was built for horses, not cars. Repairs will close the bridge for several months, causing bigger jams and more pollution in a city where air quality is already a cause of concern.

Bath is an extreme example of a tradeoff faced by much of the country. Britain has the oldest housing stock in Europe, with one in five homes more than 100 years old. Period features are valued and often protected by law. Yet as efforts to cut carbon emissions intensify, they are contradicting attempts to preserve heritage. It is a “delicate balance” says Wera Hobhouse, Bath’s Member of Parliament (议员) “What is the public benefit of dealing with the climate emergency, versus protecting a heritage asset?”

Two years ago, Bath was among the first British cities to declare a “climate emergency” when it also promised to go carbon-neutral by 2030. Yet Bath also wants—and is legally required to preserve its heritage. With Roman remains and Georgian streets that spread across the Avon Valley in shades of honey and butter, the city is designated a world heritage site by UNESCO. About 60% of it is further protected by the government as a conservation area, more than 5,000 of Bath’s buildings—nearly 10% of the total—are listed as being of special architectural or historical interest, making it a criminal offence to alter them without permission.

Many of the features that make Bath’s Georgian buildings so delicate also make them leaky. Buildings of traditional construction make up 30% of Bath’s housing stock but take up 40% of domestic carbon emissions, according to the Centre for Sustainable Energy, a charity. British homes are rated for energy efficiency on a scale from A to G; most traditional buildings in the city are an F or G.

Transport is another area where climate and heritage clash. Bath’s 17th-century streets lack room for bike lanes. Joanna Wright was recently relieved of her role as Bath’s climate chief after proposing that North Road, which leads to the university, should be closed to traffic. In two years she was unable to install any on-street electric-vehicle charging points, partly because of the “nightmare” of getting permission to dig up old pavements.

All this means going carbon neutral by 2030 looks hard, but the city is at least beginning to make compromises. In March it launched the first “clean-air zone” outside London, charging drivers to enter central Bath. A trial has made 160 electric motoreycles available to hire. And local opinion seems to be shifting in favour of sustainability. “The discussion has moved dramatically towards considering the climate emergency,” says Ms. Hobhouse.

Sometimes we may find that every week there are a lot of new stories about how climate change is affecting the planet, or new plans to battle its effects. But the concept itself isn't new at all --- in fact, scientists have been exploring questions about climate change for almost 200 years.

The idea of “greenhouse gases” goes back to 1824, when Joseph Fourier wondered what was regulating the earth's temperature. Fourier concluded that the atmosphere must be responsible for containing the heat absorbed from the sun and described it as a box with a glass lid: As light shines through the glass, the inside gets warmer as the lid traps the heat. As Fourier's ideas spread, it came to be called “the greenhouse effect”.

Scientists continued to study the greenhouse effect. Not until a Swedish chemist named Svante Arrhenius came along, did scientists understand how global warming actually works. After years of work, Arrhenius determined that the level of carbon dioxide in the atmosphere did in fact have a direct effect on global temperatures.

Arrhenius found that CO₂, and other gases trap radiation, which warms the atmosphere. Arrhenius was the first to suspect that burning coal could contribute to the greenhouse effect. But Arrhenius welcomed the warming effect on the planet. At a lecture later that year, Arrhenius noted that creatures of a warmer earth “might live under a milder sky and in less barren surroundings”.

While Arrhenius' findings won him the 1903 Nobel Prize in chemistry, scientists kept debating whether the greenhouse effect was increasing until 1950, when researchers finally began to find strong data supporting it. By the end of the 1950s, American scientists had been sounding the alarm on the long-term consequences of climate change. Climate change research has come a long way since Fourier first described the greenhouse effect – still, maybe Arrhenius should have been more careful of what he wished for.