2 . Sustainability was a hot topic at the Paris Air Show, the world’s largest event for the aviation industry, which faces increasing pressure to reduce the climate-changing greenhouse gases that aircraft emit. Even the massive orders at the show got an emission-reduction perspective: Airlines and producers said the new planes would be more fuel-efficient than the ones they replaced. However, most of those planes will burn conventional kerosene-based jet fuel.

Some companies are working on electric-powered aircraft, which are seen as a way to reduce the environmental effects of the aviation industry, providing zero emissions and quieter flights. However, they are still some way off from widespread commercial use. That means sustainable aviation fuel (SAF) has become the industry’s best hope of achieving its promise of net zero emissions by 2050. SAF, however, accounts for just 0.1% of all jet fuel. Made from sources like used cooking oil and plant waste, SAF can be mixed with conventional jet fuel but costs much more.

With such a limited supply of SAF, critics say airlines are making overly ambitious promises and exaggerating how quickly they can ramp up the use of SAF. The industry even has skeptics: Nearly one-third of aviation sustainability officers in a GE Aerospace survey doubt whether the industry will hit its net zero goal by 2050.

Across the Atlantic, a consumer group called BEUC filed a complaint against the European Union’s executive arm, accusing 17 airlines of greenwashing. The group says airlines are misleading consumers and breaking rules on commercial practices by encouraging customers to pay extra to help finance the development of SAF and offset future carbon emissions created by flying. In one case, the group’s researchers found Air France charging up to 138 euros for the green option.

“SAF is indeed the biggest technological potential to decarbonize the aviation sector, but the main problem is that it isn’t available. We know that before the end of the next decade — at least — it won’t be available in massive quantities,” said Dimitri Vergnc, a senior policy officer at BEUC.

4 . The Forest Eye project aims to create the largest living forest feature in England by growing 5,000 alder, beech and maple trees into the shape of a child’s eye. The trees are being planted in Dalby Forest, North Yorkshire, with the help of local young people. The trees will form an eye 300 meters wide that will be visible from the sky in about six years, when they have grown.

The project hopes to focus on the importance of young people’s ideas for creating a health y natural environment. It was designed by a company called Sand in Your Eye and has been created by Forestry England, an organization that protects forests and woodlands.

Josephine Lavelle, director at Forestry England, says, “Having the gaze of a child growing in the heart of this beautiful and ever-changing forest is a powerful symbol of how we need to listen and respond to the needs and vision of future generations.”

The project also aims to highlight the important role that forests play in fighting climate change. As well as providing a home for wildlife, trees absorb carbon dioxide from the atmosphere and create oxygen that humans need to breathe. When the trees have grown, they will provide a place for lots of wild animals, like bats, birds and small mammals to live. The Forest Eye will also create a space for people to explore and connect with nature.

Jamie Wardley, artistic director at Sand in Your Eye, has plenty of experience creating pieces of “land art”. These are huge drawings and sculptures made from grass, ice and sand, including a 60-meter portrait of Swedish climate-change campaigner Greta Thunberg on a school field in Yorkshire. He says, “The trees are my paint.” “Our work is about prompting people to think deeply and respond emotionally to some of the biggest issues facing us, including the climate crisis.” Wardley also plans to develop the Forest Eye into an even bigger project. “It is our ambition to create the whole face of a young girl at the same scale, measuring 2,000 meters across. Those trees that are planted in the Forest Eye are the very beginning of this,” he says.

10 . From lettuces (生菜) farmed on New York’s skyline to thick corridors of trees occupying Colombian roadsides, green initiatives are running wild in cities around the world.

Replanting initiatives have sprung up since the start of the 21st century as urban development goals have shifted and alarm about global warming has grown.

In nine cities around the world, thanks to planting schemes on walls and roofs, the temperature can be reduced by 3.6 to 11.3 degrees Celsius (摄氏的) at the hottest time of day, according to a report by the French Agency for Ecological Transition. Green spaces have also been shown to improve health and well-being, including by reducing stress, anxiety and depression, improving attention and focus, bettering physical health, said Stephanie Merchant of Bath University’s department for health. “However, it’s about where they are created in relation to the needs of the local communities,” she added.

So, are all urban replanting projects worthwhile?

“For a scheme to be seen as effective, it must fulfill as many functions as possible,” said the economist and urban planner Jean Haentjens. In addition to lowering the temperature, he said it should also preserve biodiversity, improve well-being, raise awareness, be appealing to residents and suitable for its social context.

The Brooklyn Grange rooftop farm in New York grows more than 45 tonnes of organic produce a year. Covering three rooftops, totalling more than 22,000 square metres, the farm cultivates a wide variety of vegetables. But it has to limit the soil depth to about 30 centimeters and irrigate (灌溉) the soil a little more frequently, because it dries out very quickly. Another question is whether pesticides (杀虫剂), which scare off birds and insects, are used when the aim is to boost biodiversity. For Jean Haentjen, it represents “an interesting route”, depending on the context. “But we can’t make it the model of tomorrow,” he said.