【推荐1】Commercial aviation (航空) alone contributes around three percent of total global carbon emissions (排放). But the industry is actively looking for green solutions in the form of sustainable aviation fuel (SAF). In a study released this week, a team of researchers from the U. S. Department of Energy’s National Renewable Energy Laboratory (NREL) details a method of transforming food waste into SAF that can be used in existing engines. Making SAF is a more complicated process—it’s got to be very similar to the petrol-based aviation fuel we use today in commercial flights.

The researchers use volatile fatty acids (挥发性脂肪酸)(VFAs) from smelly food waste and transform it into simple paraffin molecules (石蜡分子) that can be used in fuel and really aren’t all that chemically different from traditional emissions-heavy fuels. There are other renewable biofuels that have been made from biomass (生物质), specifically oil and fat from vegetables and animals, but using the ever-mounting pile of food waste to fuel flights broadens those possibilities.

Derek Vardon, a senior research engineer at NREL, says major companies are eager to get involved in SAF because some sustainable solutions, such as battery-operated commercial flights, just aren’t possible yet with current battery technology. A battery-powered plane would be too heavy to fly long distances—“So using SAF that works in the same way as the fuel we have is a simpler way to trade out traditional emissions-heavy fuels.” Vardon also says that “because the wet waste would normally go to a landfill and break down to release greenhouse gases, the process of making and using SAF could actually have a negative carbon footprint when it is dramatically used.”

A major question as the researchers move forward with this type of research is if it is possible to run an airplane engine on fully renewable biofuel. Rolls-Royce recently did a test on one of their engines with 100 percent SAF and it worked. “This fuel is not crazy and we can solve these problems,” Vardon says.

【推荐2】When we think of Antarctica, the first thing that comes to our mind is a picture of penguins and large areas covered with snow. Large amounts of white snow spreading over thousands of kilometers is a pretty good description of Antarctica.     1    

Research and observations conducted over the past few years have led to the conclusion that the Antarctic Peninsula's snow is turning green.     2     These algae (藻), even though they are individually incapable of being seen by eyes, are visible from space. These algae produce colonies called algal blooms, which spread over large areas.

    3     As a result, Antarctica is visible as many patches of green algae are on white snow from space. Algae are green because of the presence of the pigment chlorophyll, which helps in photosynthesis (光合作用). Not just green though, red algae have also been found on Antarctica's snow, leaving the snow painted red. These green and red algae are not just present on the surface of the snow.     4     When the upper layer of snow melts, the algal bloom remains visible in the layers below.

Scientists fear that such profound growth of algae can set off more global warming, causing even more snow to melt. To better understand that, we must consider that white snow reflects most of the sunlight that falls on it. However, as the surface of the snow darkens, it absorbs more and reflects less of the sunlight.     5     This will cause warming of the surrounding area at a faster rate, melting more snow day by day.

【推荐1】Leap days（闰日）play an important role in keeping our calendars on track. It's all thanks to Julius Caesar.

Most years, the calendar is made up of 365 days. However, the Earth's turning around the sun is actually a little longer than that. It's about 365 1/4 days. This makes the calendar year a bit shorter than a solar year. If you're trying to set up an exact system for measuring the passing of time and changing seasons, this throws small trouble in the work. That was back in 46 B. C. when Julius Caesar was developing what came to be known as the Julian Calendar. He decided that every four years an extra day would be added to the calendar on the advice of an astronomer, Sosigenes.

At first, Caesar's way seems simple and direct. You “bank” those extra quarter days for a few years, and then spend them on a leap day. But as the centuries went on, people began to notice something was wrong—it was speeding ahead of the solar year. By the end of the 16th century, the calendar year had been as much as 10 days ahead. The solar year is actually a little shorter than Caesar and Sosigenes thought. “It's not exactly a quarter of an extra day. It's a little less,” says physicist Judah Levine. “So adding one day every four years was too much.”

Astronomers now know that a solar year is actually 365. 24219 days long. This may not seem like much under the Julian Calendar, but that little mistake led to about 11 minutes off a year. So in 1582, Pope Gregory decided to reset the calendar. He came up with something called “the century rule”. If the number of years is a multiple（倍数）of 100 and is divisible（可整除的）by 400, and if the number of years is not a multiple of 100 and is divisible by 4, an extra day is added. Pope Gregory was also responsible for setting leap day as February 29.

The calendar won't skip（跳跃）another leap year until 2100. That little setup has kept our calendars fairly accurate（精确的）for over 400 years.

【推荐1】Mutualism—win-win ecological partnerships perfected over evolutionary time-lengths—is a less-known ecological relationship that is also weak and easily hurt by the effect of a rapidly changing planet.

Bees and flowers are typical examples of mutualism. Some bee tongues are perfectly evolved to tap into certain flowers. By specializing in those plants, the longer-tongued bees reduce competition with insects that can't access those sweet foods.

That mutualistic relationship, however, has been impacted in at least one population of bees and flowers. As certain flowers in Colorado have become rarer due to warming temperatures, the tongues of the bumblebees（大黄蜂）that historically fed on them have become shorter.

Like many of their relatives, bumblebees are on the decline. To find out what's going on, a team of researchers headed to Colorado. The researchers examined bumblebee samples collected on three mountains from 1966 to 1980 and also gathered a fresh set, which they collected in the same places from 2012 to 2014. They performed the task of measuring all the historic and recently caught bees' tongues.

As the team reports in Science, both of the species tongues have declined in length over time. The team found a nearly 25-percent decrease in tongue length between the bees collected decades ago and those living in the same region today.

Next they turned to the flowers. Looking at contemporary and historic botanical data, the scientists confirmed that the number of flowers with short tubes did not increase in large quantities. They found that in response to warmer temperatures, flowers have been moving up the mountains and becoming rarer at lower altitudes. This altitude-climbing effect has ultimately resulted in an approximate loss of millions of flowers.

The findings paint a telling picture: hotter summers caused bumblebees' choice flower species to disappear, forcing them to evolve shorter tongues to tap into the remaining food sources. Then, competition with generalist species, more time and energy needed and a forced reliance on alternative sources all likely contributed to the bees' overall decline.

【推荐3】Scientists have long considered the question of whether and how plants communicate. For years, the topic sparked controversy. Books like 1973’s The Secret Life of Plants suggest that plants grow well if you sing or play classical music. Such statements were later debunked: Any evidence that music helps plants grow is not convincing at all. Still, researchers firmly believe there is some sort of communication going on between plants.

Plant communication is a complicated topic. What we do know is that plants have a wide range of mechanisms for communicating with each other and their surroundings. “It’s quite clear that plants are not just unresponsive victims, but that they are very aware of nearby things,” says Richard Karban, an entomologist at the University of California. “And they respond to reliable information.”

When a plant sends out chemicals in the air in response to a perceived threat, other sensitive leavcs on that same plant, as well as the leaves of their neighbors, perceive those signals and subsequently increase their own defenses. Karban’s research, for instance, shows that plants sound the alarm when they’re attacked by pests, so that other plants respond by growing faster and stronger. Even other species, like tobacco, can sense and react to the alarm.

In a study published in the journal Cell this March, Lilach Hadany, a professor at Tel Aviv University, put tomato and tobacco plants in an isolated box and then recorded ultrasonic (超声的) sounds. They experimented with, cutting stems or leaving them without water to simulate drought. The researchers found that the plants emitted (popping and clicking sounds at around 60 decibels in response, approximately as loud as human chatter. These sounds were at an ultrasonic frequency that humans can’t naturally hear, however. Hadany’s team even matched different sounds to the plants’ environment. And each type of stress could be matched with a specific, identifiable sound.

“We don’t know if they’re using the sound, or if the sounds are emitted in a completely passive way due to physiological changes,” Hadany says. “But we do know they are in the air, and they contain information.”