A team of scientists says that playing sounds underwater can get fish to return to areas with severely damaged coral reefs(珊瑚礁).

In an experiment, they found fish returned after hearing recordings of the sounds of a healthy ocean reef. The scientists placed underwater speakers in areas where coral had been dying in Australia’s northern Great Barrier Reef. They played the sounds over a period of about six weeks in 2017 and studied the results. The team reported that twice as many fish arrived in areas where the sounds of healthy coral were played. The sounds also led to a 50 percent increase in the number of species present in the area, the researchers found. Among the arriving fish were species that feed on all major food sources.

The researchers noted the importance of having many different kinds of fish return to the area. Different species of fish perform many activities that support the ocean environment and sea life. “Damaged reefs have a higher chance of recovery if they have healthy fish populations,” the scientists wrote in the report.

Steve Simpson is a professor at the University of Exeter who helped lead the research. He said in a statement that “healthy coral reefs are remarkably noisy places”. They contain the sounds of many kinds of shrimp, fish and other sea creatures. Young fish listen for these sounds when they are looking for a place to settle, Simpson said.

He added that reefs “become ghostly quiet” when they suffer destruction that is usually related to human-caused pollution. Coral damage can cause unappealing smells and sounds that drive shrimp and fish away. But the experiment suggested that the use of underwater loudspeakers was an effective way to get young fish to come back.

Andy Radford, a professor at University of Bristol, said the underwater sounds are a promising way to fight coral reef damage at the local community level. But he noted that other threats need to be, reduced as well. These include climate change, pollution and overfishing.

Two years ago, enormous fires swept through some 46 million acres of forest in Russia, the country’s worst fire season on record. Now, researchers have a clearer sense of just how significant the 2021 boreal(北方的)forest fires were in terms of emissions. The fires produced more planet-heating carbon dioxide than any other extreme fire event that has occurred since the turn of the 21st century, according to a study.

Boreal forests grow where it is very cold. The trees that live in this type of forest grow slowly and seal (封存) carbon in their trunks and roots for hundreds of years, comprising a collection of trapped emissions that researchers call a carbon sink. But rising temperatures and related drought in these historically cool regions have led to an increase in extreme wildfire activity and threaten to release the carbon stored in the trees that grow there, transforming a carbon sink into a carbon source.

In all, fires in boreal forests released the carbon sink and produced nearly half a billion metric tons of carbon in 2021.That’s more carbon than the entire continent of Australia produced the same year, though some of the emissions produced by the fires will be sucked back up as forests regrow.

The researchers obtained the data for their study by tracking concentrations of emissions in the atmosphere using satellites, and then they put that information into a computer model to determine where, geographically, those emissions came from. They found that boreal forests, which typically produce about 10 percent of the globe’s annual wildfire emissions, accounted for 23 percent of the world’s wildfire emissions in 2021—more than twice as much as normal.

Canadell, who led the study, is most concerned about the study’s main takeaway; Boreal forests have served an important and underappreciated role in sequestering carbon emissions, but climate change threatens to release that carbon. “We need to be very careful with these systems in terms of their future development,” he said.

A major new facility to pull carbon dioxide out of the atmosphere started operating in Iceland on Wednesday. The carbon capturing plant is the biggest of its kind, its builder says, increasing global capacity for the technology by more than 40 percent. Many climate experts say that efforts to suck CO₂ out of the air will be key to making the world carbon neutral(碳中和)in the coming decades.

By 2050, humanity will need to pull nearly a billion metric tons of CO₂ from the atmosphere every year through direct air capture technology to achieve carbon neutral goals according to International Energy Agency recommendations in 2021. The plant in Iceland will be able to capture 4,000 metric tons annually—just a tiny amount of what will be necessary, but it can grow rapidly as efficiency improves and costs decrease.

For now, the plant in Iceland is an unlikely global protector. Human-sized fans are built into boxes that are the size of standard 40-foot shipping containers. They sip CO₂ out of the air, catching it in sponge-like filters(过滤器). The filters are heated at a high temperature needed to boil water freeing the gas. Then it combines with water to produce a mixture, which is pumped deep underground, where over time it cools down and turns into dark-gray stone.

Pumping CO₂ into the ground is just one way to dispose of it. It can also go to other uses, as well. Energy companies can mix the carbon dioxide with hydrogen to make fuel. Farmers can feed their plants with it. Soda manufacturers can use it to make their drinks bubble when there is a carbonation shortage.

At the moment, the costs are high: about $600 to $800 per metric ton of carbon dioxide, Gebald, the cofounder of Climeworks, said far from the levels around $100 to $150 per ton that are necessary to turn a profit without any financial help of the government. In the long term, Gebald thinks prices will be half that by the late 2030s—about the price where it will be a competitive method of reducing global emissions.