Tropical Biofuels Getting Less and Less Green

Picture of rainforest

Knockdown fight. New research suggests that using tropical rainforests to grow biofuels could be even trickier than previously estimated.

A new analysis suggests that biofuels grown in the tropics are not a much greener source of energy than drilling for oil–at least in the short term. The research paints an even gloomier picture of biofuels than previous studies, which have begun to cast doubts on the greenhouse gas benefits that these alternatives to petroleum might provide.

Proponents see plant-based biofuels as a carbon-friendly alternative to fossil fuels. That’s because plants that produce, say, palm oil or corn ethanol recycle carbon dioxide from the atmosphere as they grow. In contrast, petroleum production introduces new carbon into the air that was previously sequestered deep within Earth.

Two studies published earlier this year in Science, however, suggest that the carbon benefits from biofuels are delayed for centuries when farmers knock down carbon-absorbing forests in order to grow the plants. One paper, for example, estimated that cutting down Brazilian rainforest to grow soybeans for diesel fuel would result in a so-called carbon debt that would take 319 years to repay–essentially rendering the fuel as carbon-unfriendly as gasoline in the short term.

But critics, including the U.S. Department of Energy, have charged that such analyses underestimate the yield of biofuel crops, especially those grown in the tropics.

To get a better sense of just how green biofuels are, Holly Gibbs, a tropical land-use scientist at the University of Wisconsin, Madison, and colleagues used newly available data on the yields of 10 crops in various seasons and ecosystems within South American, African, and Asian rainforests. Even when Gibbs assumed that the plants would perform in the top 10% of all global varieties–with corn ethanol varieties, for example, producing more than seven times as much ethanol as current species in Africa–the picture remained gloomy. For example, corn grown with high yields in tropical forests (thanks to fertilizer, irrigation, and sophisticated farming) repaid its carbon debt in 100 years: five times faster than corn grown at normal yields. But the improvement is still a "losing proposition," Gibbs says, given the goal of stemming carbon emissions immediately. What’s more, she notes, such yields would be hard to achieve throughout the developing world anyway given the cost of world-class agriculture.

To make biofuels more efficient, Gibbs suggests growing biofuel crops in places where trees wouldn’t have to be cut down, such as in West African scrublands where cocoa plantations once grew. Otherwise, growing, say, oil palm trees on land that was previously carbon-rich peatland forests in Southeast Asia can create a nearly millennium-long carbon debt, the team reports online today in Environmental Research Letters. The paper highlights the short-term risk of ramping up production of tropical biofuels and cutting down carbon-rich forests to grow them, says Gibbs.

The new studies offer a set of estimates more precise than before for the carbon tradeoff that biofuels entail, says Princeton University agricultural expert Timothy Searchinger, an author of one of the Science papers. "Forests and grasslands have a lot of carbon, so there is really no way to transform those lands into biofuel crops that produce net benefits," he says.



A Trickle on the Moon

Picture of volcanic glass bits

Beady clues. Water molecules lurk in these volcanic glass bits from the moon’s surface.

Credit: NASA

A team of researchers has discovered the first evidence of water on the moon. A new type of chemical analysis has spotted the telltale signs of water molecules inside tiny beads of volcanic glass brought to Earth decades ago by the Apollo astronauts. The find may force astronomers to rethink their theories of how the moon formed, and it might mean that future missions could mine water from the lunar soil, helping to sustain colonists and fuel voyages to other planets.

Soon after it coalesced, about 4.5 billion years ago, Earth took at hit from a Mars-sized object. The resulting cloud of debris eventually condensed to form the moon–or so the current thinking goes. But if the moon came from Earth, and Earth is awash with water, where is the lunar water?

Many planetary scientists think any water blown away from Earth by the impact would have been instantly vaporized by the high temperatures of the collision. Nevertheless, some researchers continue to believe that the moon does contain some water, perhaps locked deep within its interior. Over the years, they’ve intensely scanned tiny glass beads–brought back by the Apollo missions in the 1960s and 1970s–that had been ejected from inside the moon by volcanic eruptions about 3 billion years ago. Up to now, however, these samples have shown no evidence that the liquid ever existed on the moon.

A team led by geochemist Alberto Saal of Brown University decided to use a more sensitive method. The technique, called secondary ion mass spectrometry, was developed to detect trace amounts of volatile gases such as chlorine and fluorine in Earth soil samples. Applying it to the lunar samples, the team found trace amounts of water–about 46 parts per million–in the volcanic beads. Because the water was embedded in the beads, it can’t be a contaminant picked up since the samples arrived on Earth, the researchers report tomorrow in Nature.

Saal declines to speculate about how much water the moon contains or if any of it is still present in liquid form. Extrapolating the results to estimate the amount of lunar water would be like predicting "the final score of the game after we saw the first touchdown in the first 5 minutes of the first quarter," he says. Meanwhile, he and his team will be studying as many lunar glass beads as possible to refine their analysis.

Planetary scientist David Stevenson of the California Institute of Technology in Pasadena calls the findings important and says they open up a new possibility. "It is likely that at the time of the giant impact, Earth had water and the impacting body had water," he says, so some of that water might still be trapped in the moon.

Rain on the Martian Plain?



Picture of channels

Before the rains came. Martian water may have carved out channels like these early in its history, but eventually the torrents were replaced by light rain.

Martian soil data collected by five robotic missions indicates that rain fell on the Red Planet billions of years ago. The findings provide no new insight into the possibility of martian life, but they do suggest that further clues to Mars’s past could be found right here on Earth.

There’s little doubt now that Mars once was wet. The twin Mars Exploration rovers–Spirit and Opportunity–have been finding signs of water-associated minerals for 4 years now. And less than 2 weeks ago, the Phoenix Mars Lander struck water ice while digging at the north polar region (ScienceNOW, 20 June). What remains to be determined is where this wetness came from and how long it lasted. Preliminary investigations by Mars mission scientists, as well as high-resolution images taken by orbiters, have suggested that water on Mars surged up from deep below the surface, sometimes carving extensive channels and gullies (see photo).

Now, a team led by geologist Ronald Amundson of the University of California, Berkeley, has found indications of rain by studying our own planet’s geochemistry. Analyzing soil samples collected by five previous missions, including the 1976 Viking and 1997 Pathfinder landers, the researchers found a distinctive pattern of chloride and sulfate deposits. In all of the samples, the data show that the sulfates tend to stay nearer to the surface, whereas chloride concentrations increase with depth. That’s the same pattern found in extremely arid places on Earth such as Antarctica’s dry-valley regions and Chile’s Atacama Desert. In these areas, rain is light and infrequent, but over millions of years it can change the chemical makeup of soil by depositing sulfates near the surface and by transporting the more soluble chlorides farther into the soil.

So the picture emerging is that by about 3 billion years ago, the biggest bodies of water on the martian surface, which were derived from groundwater, had mostly frozen or evaporated, the researchers report online this month in Geochimica et Cosmochimica Acta. Then a prolonged period of intermittent drizzle and dew began. That climate apparently continued long enough to alter the chemistry of surface minerals, creating the pattern detected by the analyses.

It’s a convincing argument, says planetary scientist Itay Halevy of Harvard University: "Atmospherically delivered water and downward migration of salts, both common processes on Earth, played a part in the formation of martian soils, too." Moreover, the results "provide further chemical support for what previous studies have found: that during early parts of Mars’s history, liquid water existed on the surface for geologically significant periods of time."

Pollutants in the deep-ocean food web

Scientists say the concentrations of pollutants they documented in deep-sea squid are surprising?

Research published online May 22 in Marine Pollution Bulletin presents new evidence that human-made contaminants are finding their way into the deepest parts of the ocean. The paper is one of the first reports of persistent organic pollutant uptake by deep-sea mollusks, an important part of the marine food chain.

This deep-sea mollusk, <em>Histioteuthis reversa</em>, is called the jewel squid because of its many photophores, or light-producing organs, which appear as dark dots on its skin.

This deep-sea mollusk, Histioteuthis reversa, is called the jewel squid because of its many photophores, or light-producing organs, which appear as dark dots on its skin.

A team of researchers from the Virginia Institute of Marine Science and the National Marine Fisheries Service (NMFS) collected nine species of cephalopods, a class of organisms that includes octopods, squids, cuttlefish, and nautiluses, from depths between 1000 and 2000 meters (about 3300 to 6600 feet) in 2003 in the western North Atlantic Ocean. The team selected species for chemical analysis on the basis of their importance as prey and analyzed specimens for 11 classes of anthropogenic chemical contaminants. The compounds the researchers detected include DDT, PAHs, PCBs, PBDEs, tributyltin, and toxaphene.

“It was surprising to find measurable and sometimes high amounts of toxic pollutants in such a deep and remote environment,” says coauthor Michael Vecchione of NMFS.

Although scientists have previously looked for persistent organic pollutants in deep-sea fish, there is little information on such chemicals in deep-sea cephalopods. The large variety of contaminants that the scientists reported in the new paper makes it “apparent that contamination of the deep-sea oceanic food web is occurring,” they write.

“The cephalopod species we analyzed span a wide range of sizes and represent an important component of the oceanic food web,” Vecchione says. He explains that he and his colleagues initiated the study in response to recent reports documenting the accumulation of persistent organic pollutants in the blubber and tissues of whales and other predatory marine mammals as well as in some deep-sea fish. The researchers set out to determine whether whales have a unique capacity to accumulate pollutants or are simply one of the top predators in a contaminated deep-sea food web. The finding that cephalopod tissues contained some of the same compounds that have been reported to bioaccumulate in marine mammals points to the latter hypothesis.

“Contamination of the deep-sea food web is happening, and it is a real concern,” Vecchione concludes.



  • Antarctic iceCrash! In one doomsday scenario, global warming triggers titanic chunks of ice to break and slide off the Antarctic landmass, causing sea levels to rise by meters. The surrounding Antarctic ice shelf has been splitting over the past 2 decades–but is this a harbinger of doom or just part of some natural cycle? Researchers using underwater acoustic sensors originally designed to detect nuclear explosions have listened to the grinding and cracking of the ice, and they have now determined that–at least over the past 7 years–there has been no increase in Antarctic ice shelf break-up. The results, reported this week at the Acoustics 2008 meeting in Paris, France, provide a baseline for the rate of Antarctic splitting. The question now is whether it will increase as the temperature rises.




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* 污染环境修复以及资源综合利用;

* 清洁生产与风险评价;

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古力特心中历史最佳11人:超级锋线 球王非他莫属


  新浪体育讯 足坛巨星古力特接受英国《442》杂志邀请,评出了自己心中的历史最佳11人阵容。