【推荐3】Climate change has been a long-standing issue that continuously drives scientists to find green, sustainable fuels. The universe's most abundant element, hydrogen（氢）, has grabbed their attention and is now on its way to becoming the future of green fuel.

More than $150 billion worth of green hydrogen projects were announced globally in 2020. Airbus, a European multinational aerospace corporation, has taken the lead in the new sustainable fuel industry. It has designed self-contained hydrogen fuel cell pods（燃料电池舱）that can be attached to the underside of airplane wings, promoting the use of hydrogen fuel for long-distance flights, which aim to achieve zero emissions. The company plans to launch hydrogen-powered aircraft in 2035, according to Daily Mail.

Compared to fossil fuels, hydrogen is a much more eco-friendly fuel. When hydrogen burns, the only by-product is water. However, the traditional way to extract（提取）hydrogen from natural gas or coal generates considerable carbon emissions. The greenest way is to obtain hydrogen from water using electrolysis（电解）powered by renewable energy, although this process requires so much electricity that it is quite expensive. The key to making hydrogen competitive with fossil fuels is to lower the production cost to under $1.50. This would require lowering around 50 percent of renewable power costs and 75 percent of electrolyzer costs, according to Australia's renewable energy agency.

Also, shipping liquid hydrogen is challenging, given that needs to be chilled to -253℃ to do so. Japan's Kawasaki Heavy Industries is set to complete the construction of the world's first liquefied hydrogen carrier by early 2021. Most of the world's big hydrogen export projects are looking to ship hydrogen in the form of liquid ammonia（氨）, which can be converted to hydrogen and needs to be chilled to only -33℃.

With more and more countries aiming to cut down carbon emissions to tackle the issue of global warming, green hydrogen will help them hit the targets by decarbonizing industries that cannot be electrified.

"We could use these circumstances, where loads of public money are going to be needed into the energy system, to jump forward towards a hydrogen economy," said Diederik Samsom, the leader of the European Commission's climate cabinet.

【推荐1】Happy news arrived from Colorado this week as Colorado Parks and Wildlife (CPW) announced that two wolves, John M2101 and Jane F1084, had been spotted with multiple pups (幼崽). The gray wolves and their pups were first sighted by a wildlife biologist and CPW district wildlife manager. The good news follows the decision to reintroduce gray wolves to the state just last year.

To gain further confirmation, CPW staff conducted three separate observations to see what was happening at the den (窝) from a safe distance. This confirmed the presence of the collared wolves John and Jane, who were joined by three pups. The true group size remains to be seen, however, as it’s possible there may be more that have not yet been spotted. Gray wolf dens usually contain around four to six pups.

“Colorado is now home to our first wolf den since the 1940s,” said Governor Jared Polis in a statement. “We welcome this historic den and the new wolf family to Colorado. With voter passage last year of the project to require reintroduction of the wolf by the end of 2023, these pups will have plenty of potential mates when they grow up to start their own families.”

“It’s incredible that these two adult animals have traveled the distance and overcome the challenges they have to get here, and to now have pups in Colorado,” said Kris Middledorf, area wildlife manager for CPW. “Our first duty is to ensure that they have the chance to boom, so even as we have exciting news, we want to remind everyone that these animals remain endangered in Colorado.”

The status of gray wolves is backed up by law in the western state, where killing an endangered species can result in the removal of hunting privileges, a fine of $100, 000, and even jail time. It’s also prohibited to hunt wildlife in the state— but with acute hearing and excellent eyesight, leaving these smart animals should be easy enough if you don’t go looking for them.

【推荐2】Zoologists track animals using global-positioning-system(GPS)tags(标签) which then return their data via satellite. Marine(海洋的)biologists have a harder time of it, though, because radio signals can’t pass through seawater. This makes it impossible either to receive GPS signals or to send any data collected back to base.

That does not stop people tagging sea creatures. Data collected and stored in a tag can be sent to a satellite in bursts if the species in question is one that comes to the surface from time to time. A tag may also be recovered if the animal carrying it is caught by a fishing boat. Fisherfolk are typically paid a few hundred dollars per tag returned to its home laboratory.

None of these methods, though, keeps accurate track of where the animal carrying the tag has been. For these and other reasons, it would therefore be useful to have a marine equivalent of GPS. And one is now being employed. The Woods Hole Oceanographic Institution, in Massachusetts, hopes to fill the seas with sonic beacons(声波信标) that will play the role of GPS satellites.

The sea is divided into distinct layers that have different temperatures. During the Second World War, American scientists showed that some of these layers act as sonic waveguides. They called them “sound fixing and ranging” (sofar) channels. Sound sent out in one of these channels echoes(回响) between the layers above and below, thus staying in the channel. Thus constrained(被约束)，a sound wave can travel hundreds of kilometers before it becomes too weak to detect.

The sofar transmitters from Woods Hole are usually at an appropriate depth for the channel concerned. Every 12 hours they broadcast a 32-second-long location signal known as a pong. Pongs are so called because they are similar to sonar “pings”, but of lower frequency. In typical conditions a pong can be picked up 1,000 km away. By listening to the pongs from several beacons a receiver can calculate its location. Existing receivers for the two sofar transmitters are currently carried on free-floating instrument packs. But the plan is to have two more transmitters this year, and more in future years.