2 . Balancing Forests and CO₂

Tree planting used to be regarded as an effective means of curbing (抑制) climate change. Perhaps it’s time for us to rethink this practice.

Trees pull carbon dioxide or CO₂ from the air. This effectively removes CO₂ from the atmosphere, making trees an important part of the fight against climate change. But trees only hold onto carbon dioxide as long as they’re alive. Once they die, trees decay (腐烂) and release that CO2 back into the atmosphere. This movement of carbon between forest and the atmosphere is called a carbon flux (碳通量), a natural process that happens as trees grow and eventually die.

Recent studies have found that trees around the world are growing faster than ever. Rising atmospheric CO2, mainly due to burning fossil (化石) fuels, is probably driving that rapid growth, said Roel Brienen, a forest ecologist at the University of Leeds, UK. High levels of this gas are boosting temperatures, which in turn speeds tree growth in those areas, he added.

The faster trees grow, the faster they store carbon. It seems like good news. However, it is known that fast-growing tree species, in general, live shorter lives than their slow-growing relatives.

In order to see whether the growth-lifespan trade-off (生长和寿命之间的权衡) is a universal phenomenon, Brienen and his colleagues analyzed over 210,000 individual tree ring records of 110 tree species from more than 70,000 sites worldwide. “By measuring tree rings’ widths one can tell how fast trees grew, while counting rings provides information on tree ages and allows making inferences about trees’ maximum lifespan,” Brienen explained.

They found that, in almost all habitats and all sites, faster-growing tree species died younger than slow-growing species, and even within a species, the trade-off between growth and lifespan held strong.

The team also created a computer program that modelled a forest and adjusted the growth of the trees in this model. Early on, it showed that “the forest could hold more carbon as the trees grew faster”, Brienen reported. But after 20 years, these trees started dying and losing this extra carbon again. “We must understand that the only solution to bring down CO₂ levels is to stop emitting (排放) it into the atmosphere,” said Brienen.

3 . Recently, environmentalists have encouraged us to buy local food. This reduces “food miles”, that is, the distance food travels to get from the producer to the seller. They reason that the higher the food miles, the more carbon emissions (碳排放). Buying local. food, therefore, has a lower carbon footprint and is more environmentally friendly.

However, the real story is not as simple as that. If our aim is to reduce carbon emissions, we must look at the whole farming process, not just transportation. According to a 2008 study, only 11% of carbon emissions in the food production process result from transportation, and only 4% came from the final delivery (运输) of the product from the producer to the seller.

In fact, imported food from other countries often has a lower carbon footprint than locally grown food. Take apples, for example. In autumn, when apples are harvested, the best thing for British people to do is to buy British apples. However, the apples we buy in winter or spring have been kept refrigerated for months, and this uses up a lot of energy. In spring, therefore, it is more energy-saving to import them from New Zealand, where they are in season. Heating also uses a lot of energy, which is why growing tomatoes in heated greenhouses in the UK is less environmentally friendly than importing them from Spain, where the tomatoes grow well in the local climate.

We must also take into consideration the type of transport. Transporting food by air creates about 50 times more emissions than shipping it. However, only a small number of goods are flown to foreign countries, and these are usually high value, perishable (易腐烂的) goods which we cannot produce locally, such as seafood and out-of-season berries. Even then, these foods may not have a higher carbon footprint than locally grown food. For example, beans flown in from Kenya are grown in sunny fields using human labour and natural fertilisers (肥料), unlike in Britain, where we use oil-based fertilisers and machinery. Therefore, the total carbon footprint is still lower.

It’s also worth remembering that a product’s journey does not end at the supermarket. The distance customers travel to buy their food, and the kind of transport they use will also add to its carbon footprint. So driving a long way to shop for food will wipe out any environmental benefits of buying locally grown produce.

Recently, some supermarkets have been trying to raise awareness of food miles by labelling (标记) foods with stickers that show it has been imported by air. But the message this gives is too simple. Lots of different factors contribute to a food’s carbon footprint besides the distance it has travelled.

5 . The air is thin and we have to rest several times on the short hike from camp. To our left, snow-covered mountains disappear into clouds that seem almost close enough to touch. On the grassland in front of us, we can just make out a herd of graceful animals. This is why we’re here — to observe Tibetan antelopes.

Tibetan antelopes live on the plains of Tibet, Xinjiang, and Qinghai. Watching them move slowly across the green grass. I’m struck by their beauty. I’m also reminded of the danger they are in. They are being hunted, illegally, for their valuable fur.

My guide is Zhaxi, a villager from Changtang. He works at the Changtang National Nature Rcserve. It covers an arca of about 120,000 square miles. The reserve is a shelter for the animals and plants of northwestern Tibet. To Zhaxi, protecting the wildlife is a way of life. “We’re not trying to save the animals,” he says. “Actually, we’re trying to save ourselves.”

The 1980s and 1990s were bad times for the Tibetan antelope. The population dropped by more than 50 percent. Hunters were shooting antelopes to make money. Their habitats were becoming smaller as new roads and railways were built.

In order to save this species from extinction, the Chinese government placed it under national protection. Zhaxi and other volunteers watched over the antelopes day and night to keep them safe from attacks. Bridges and gates were added to let the antelopes move easily and keep them safe from cars and trains.

The measures were effective. The antelope population has recovered and in June 2015, the Tibetan antelope was removed from the endangered species list. The government, however, does not intend to stop the protection programmes, since the threats to the Tibetan antelope have not yet disappeared.

In the evening, I drink a cup of tea and watch the stars. I think about the antelopes and what Zhaxi told me. Much is being done to protect wildlife, but if we really want to save the planet, we must change our way of life. Only when we learn to exist in harmony with nature can we stop being a threat to wildlife and to our planet.

Single-use plastic bags are used at most a few times before they     1     (throw) away. It takes them hundreds of years     2     (break) down. Many of these bags end up in the ocean where larger ones can trap sea creatures, such as turtles and dolphins. Over time, the bags fall apart into countless tiny pieces, and fish can     3     (accidental) eat some of them. Now, lots of     4     (country) and regions are taking action to ban the sale of such bags to stop people using them.

7 . Twenty years ago, crises like the California’s wildfires and Hurricane Laura that occurred last year could have been described as “natural disasters”. Thanks to climate change, this is no longer the case. Around mid-August last year, the temperature in Death Valley once reached the highest ever recorded on Earth. A hotter, drier California is much more likely to burst into flames. The Gulf of Mexico too is heating up. Hurricanes draw their energy from the warmth of the surface waters and so are becoming stronger and more likely to increase. Perhaps we should call these events in a new term, “man-made natural disasters”.

People now play such an important role on the planet. By cutting down forests and digging mines and building cities, we’ve changed half of the ice-free land on Earth. With our advanced tools, we move around more earth than all the world’s rivers and streams. As a result, all sorts of disasters extend across the line between man and nature. Many earthquakes, for example, are now caused by human activity. Meanwhile, as the climate continues to warm, wildfires will grow even larger and storms more damaging.

What’s to be done? According to some scientists, the best way to deal with human intervention in the natural world is to intervene better. Old technologies got us into this situation; new ones will get us out. Supporters of this view note the striking advances that are being made all the time, in fields ranging from computing to material science. To prevent climate change, engineers have built machines that take CO₂ out of the air. Today the numbers are limited, but perhaps one day they’ll be as common as telephones.

As for me, I think that the choice we face is not whether to change the world; that decision unfortunately has been made. The decision going forward is how are we going to change it. Over the years I’ve interviewed scores of scientists, inventors, and industrialists, and I’m continually impressed by how clever humans are as a species. But then the wind blows in smoke from 3,000 miles away, and I’m reminded of how dangerous we are as well.

One day, my two brothers and I were coming back from the islands     1     we often risked going and got more fish than others. All at once, the sky     2     (cover) with dark clouds and in less than a minute we were in a terrible storm. My elder brother put his mouth close to my ear and cried out “Moskoe-strom!” The moment I heard the word I became very frightened. And I didn’t know     3     we could survive the whirlpool or not.