Every year, about 25, 000 plastic tents are thrown away after festivals in the Netherlands. That’s enough tents to get you from base camp to the top of Everest (珠穆朗玛) if you set up a tent every metre of the way. These plastic tent not only cause a lot of pollution to the environment, but they also have to be dealt with.

Into this situation stepped the KarTent. It’s a good solution to the plastic tent problem. The KarTent is a cardboard (纸板) tent. It is put up for you at the beginning of the festival and when the festival is over, the makers pick it up, take it away and recycle it into other products. No more plastic, no more waste. The production of one KarTent produces half the CO₂ of a plastic tent. In the past, about thirty different materials were used to produce a tent. It may take hundreds of years to biodegrade (降解) the materials. However, to produce a KarTent, only one material is needed. It’s cardboard.

The tent is the brainchild of three Dutch businessmen: Jan Portheine, Wout Kommer, and Timo Krenn. After working on a cardboard beach hut, architect Jan started to look for other ways to use the skills he had learned, “In a meeting I met Wout and we found pictures of tents being left behind at festivals, and that’s how the idea started.”

Perhaps next time you’re at a festival you won’t have to look out across the sea of plastic, instead you’ll see the cardboard tents being neatly put into a truck and taken away to be recycled.

Yacouba Sawadogo,a farmer from Burkina Faso,stopped desertification (沙漠化) in his village by working together with his family to plant trees which have now grown into a vast forest. This was in response to a long dry spell (干旱期) that coupled with over-farming and over-population was bothering the northern part of the country.At first,farmers in his community thought he was going mad.

With no access to modern tools and lack of education, he started using an ancient African farming practice called zai, which leads to forest growth and improved soil quality. Gradually, the barren land was transformedi nto a forty-hectare forest containing over 96 tree and 66 plant species, many of which were eatable and medicinal, as well as a number of animals.

After doing such ground-breaking work in the African desert, Sawadogo was featured in a 2010 documentary, The Man Who Stopped the Desert, becoming famous around the world. In addition, he was awarded the Right Livelihood Award, widely known as the “alternative Nobel Prize” in 2018, “for turning barren land into forest and demonstrating how farmers can regenerate their soil with innovative use of indigenous and local knowledge”.

The technique he uses, zai, has also spread to neighboring Mali, and he teaches it to the many people who come to learn from him.“I want to design a training programme that will be the starting point for many fruitful exchanges across the region and there are so many farmers from neighbouring villages that visit me for advice on good quality seeds to plant,” Sawadogo says.“I’ve chosen not to keep my farming methods as secrets to myself”.

Today, Sawadogo is facing serious problems. Wars and conflict caused social unrest. An expansion project in the area has taken up a part of his forest. In addition, the entire family is on guard to protect the area from people wanting to steal wood. However, all these haven’t stopped the farmer’s hope.

Nearly 40 years ago, Peter Harrison, a marine ecologist witnessed the first recorded large - scale coral bleaching（珊瑚白化）event. Diving in the Great Barrier Reef（大堡礁），he was shocked by the scene before him. “The reef was made up of healthy corals and badly bleached white corals, like the beginning of a ghost city,” he says. Just months before, the same site was filled with colorful tropical life.

“Many of the hundreds of corals that had been carefully labelled and monitored finally died,” he says. “It was shocking and made me aware of just how weak these corals really are.”

Coral exists together with photosynthetic algae（藻类）, which live in its tissues and provide essential nutrition (and coloration). But high temperatures and other stresses can turn algae poisonous. When this occurs, the algae may die or be removed by the coral, a process known as bleaching because the coral’s clear tissue and white calcium carbonate skeleton（碳酸钙骨骼）are exposed. If the coral can’t reestablish its link with algae, it will starve or become ill.

The widespread destruction Harrison saw in 1982 was repeated on many other Pacific Ocean reefs that year and the next. In 1997 and 1998 the phenomenon went global, killing some 16 percent of the world’s corals. With rising temperatures, pollution, disease, increased ocean acidity, invasive species and other dangers, Harrison’s ghost cities are expanding.

Scientists suppose that about four decades ago severe bleaching occurred roughly every 25 years, giving corals time to recover. But bleaching events are coming faster now—about every six years—and in some places soon they could begin to happen annually.

“The absolute key is dealing with global warming,” says marine biologist Terry Hughes. “No matter how much we clean up the water, the reefs will die.” In 2016, a record-hot year in a string of them, 91 percent of the reefs that consist of the Great Barrier Reef bleached.