Raising a litter of teething wolf pups (幼崽) is not easy, but the wolves living in Yellowstone National Park are parenting experts. This spring, the park’s biologists shot a video of adult wolves repeatedly returning to their den (窝) with so-called “toys”—in the form of bones and sticks—to keep their little ones happy between meals.

Once they stop eating their mother’s milk, pups rely on adults to go out, hunt, and then bring back food to the den. But when that’s not possible, the adults instead retrieve odd items for the wolf pups to play with.

“Pups wait for food deliveries from successful hunts, but in the absence of food, adults bring ‘toys’,” the park wrote on Facebook. “The behavior of bringing items back to the den may be enhanced from generation to generation and probably helps keep adults from being surrounded by sharp puppy teeth.”

The adult wolves are part of “Mollie’s Pack”, one of ten known wolf packs living within Yellowstone as of January 2023. This particular pack is named after Mollie Beattie, who in 1993 became the first woman to serve as director of the United States Fish and Wildlife Service.

Beattie, who died in 1996, advocated for the reintroduction of wolves into Yellowstone National Park to help rebalance the ecosystem after the animals were systematically killed within the park Wolf reintroduction was a highly controversial initiative that many people opposed. And yet, Beattie and other wildlife managers ultimately achieved their vision and successfully relocated 41 wolves from western Canada to the park between 1995 and 1997. Today, that number has blossomed to at least 108 wolves living in Yellowstone.

Today, gray wolves are protected under the Endangered Species Act in many states. In late 2020, the administration removed the animals from the endangered list. But in February 2022, they were re-listed as endangered after a judge reversed the decision.

The destruction of tropical forests is happening at an alarming rate to make way for crops. After these lands are short of nutrients they’re abandoned, which can lead to the natural regrowth of the forest that was once there. The finding suggests that so-called recovered forests, also known as secondary forests, could play a key role in restoring ecosystems.

To better understand this process, Lourens Poorter at Wageningen University and Research in the Netherlands and his colleagues analyzed 77 secondary forest sites across the tropical regions of Central and South America, and in West Africa. These sites were all at various stages of regrowth —for example, some were 20 years old, and others were 120.

The team contrasted each secondary forest with nearby old-growth forest—forests that haven’t had major disturbance. The more similar the secondary forests were to their neighboring old-growth forests, reasoned the researchers, the more they had recovered.

The team found that after 20 years, the average secondary forest that had grown from farmland that was used with low to medium intensity (强度) had recovered 78% of old-growth forest attributes (属性). “It goes way faster than we thought,” says Poorter.

But the researchers found significant discrepancy between the recovery time for the different forest attributes. Soils were the quickest to bounce back, with most recovery happening within 10 years. It took 25 — 60 years for plant species diversity to recover.

Despite the enormous amount of deforestation that has and continues to occur, there’s hope that these forests can bounce back naturally, says Poorter. Secondary forests currently make up over 28% of tropical forests in Central and South America, and are important for locking up carbon which is important to deal with climate change.In addition, they attract mammals, birds and insects back to the area, which is important for ecosystem restoration.

“These results are promising,” says J. Leighton Reid at Virginia Tech. “However, the sites in this study don’t represent regeneration on the average piece of deforested land, and many deforested sites will recover much more slowly than the ones studied here.”

The good news is that more people bought electric cars in 2020. The bad news is that SUVs continued to grow in popularity, too. The fall in oil consumption due to the first trend was completely cancelled out by the second, say Laura Cozzi and Apostolos Petropoulos at the International Energy Agency (IEA) in France.

The growing popularity of SUVs is making it even harder to cut carbon dioxide emissions（排放）and meet climate goals. “Policy-makers need to find ways to persuade consumers to choose smaller and more efficient cars,” says Petropoulos.

Oil consumption by conventional cars – not including SUVs – is estimated to have fallen 10 percent in 2020, or by more than 1.8 million barrels（桶）a day, Cozzi and Petropoulos say in a commentary published by the IEA on 15 January. Most of this fall was due to reduced travel and is likely to be temporary.

But a small part of the drop, around 40,000 barrels a day, was as a result of the increased share of electric vehicles (EVs). “We have seen a skyrocketing of global electric car sales in 2020,” says Petropoulos. Unfortunately, the number of SUVs increased as well. While overall car sales fell in 2020, 42 percent of buyers chose SUVs, up around three percentage points from 2019.

Globally, there are now more than 280 million SUVs being driven, up from fewer than 50 million in 2010. On average, SUVs consume 20 percent more energy per kilometre than a medium-sized car.

The increase in SUVs in 2020 led to a rise in oil consumption that cancelled out the effect of electric cars, says Petropoulos. Much the same is true over the past decade. Between 2010 and 2020, global CO2 emissions from conventional cars fell by nearly 350 megatonnes, due to factors such as fuel efficiency improvements as well as the switch to electric cars. Emissions from SUVs rose by more than 500 megatonnes.

“While the growth in EVs is encouraging, the increase in SUVs is heart-breaking,” says Glen Peters at the CICERO climate research centre in Norway.

There are many reasons for the growing popularity of SUVs, says Petropoulos. Rising prosperity（繁荣）in many countries means more people are able to afford them, for instance. Some people see them as a symbol of social position. SUVs are also heavily advertised by car-makers, he says, whose profits are higher on these vehicles.

There are now some electric SUVs available. “Hopefully, in time, you will see electric vehicles entering the SUV market,” says Peters.

Even if it happens, switching to electric SUVs isn’t an ideal solution. Due to their size and bigger batteries, it takes more resources to build electric SUVs, and they consume around 15 percent more electricity. Higher electricity demand makes it harder to green the electricity supply.