NEWS | I N D E P T H
1184
ATMOSPHERIC SCIENCE
California fogs are thinning Warming linked to urbanization prevents low clouds from forming, Los Angeles area study shows
F
or years, sun worshippers have flocked to southern California’s coast, only to be disappointed each spring when the weather turns drab and foggy, a phenomenon locals call “May Gray” and “June Gloom.” But the low-hanging marine clouds responsible for that gloom have declined dramatically over the past 60 years, a new study concludes. It fingers the growth of cities and their heat-retaining concrete as a prime cause. The research, recently published online in Geophysical Research Letters, offers insight into how increasing urbanization may erode coastal fog banks in the future, with potentially serious consequences for people and ecosystems. It’s “the first definitive look at how fog might change for a specific coastal region,” says Travis O’Brien, a research scientist at Lawrence Berkeley National Laboratory in California, who was not involved in the research. To understand how California’s coastal fog might be changing, some 6 years ago lead author Park Williams, now a bioclimatologist at Columbia University’s Lamont-Doherty Earth Observatory in Palisades, New York, began assembling data from 24 southern California airports, which keep hourly records of fog conditions. He hoped to identify key climate variables influencing fog, such as sea surface temperatures and wind patterns. He revisited the data for years, but was unable to
spot any notable trends. Last year, however, Rachel Schwartz, a Ph.D. candidate at the Scripps Institution of Oceanography in San Diego, California, sent Williams a study she was finishing. It showed that low clouds had declined slightly over the past 60 years from coastal California to Alaska. But fog had nearly disappeared at the Los Angeles and Long Beach airports over a similar period, earlier studies by another researcher concluded. Those contrasting results gave Williams an idea: Perhaps the low clouds had not disappeared, exactly, but gained height. He realized that he had lumped together two potentially distinct data sets on stratus clouds, which form between the cool sea surface and a warm, stable inversion. The clouds can form close to the ground, as fog, which tends to burn off by afternoon; they can also sit higher in the sky and linger all day. Reanalyzing his data, Williams saw—at last—some intriguing trends. The lowest tier of clouds, it turned out, was heavily influenced by land use—and changing more dramatically than the higher clouds. At some airports, fog was becoming a threatened species; at one strip in Ontario, California, the average height of the summer clouds lifted by 170 meters between 1950 and 2014. That amounted to an 87% decline in the lowest clouds; summer fog that once regularly cloaked nearby mountains in moisture now visits them rarely. Overall, the Los Angeles region showed a 64% reduction in
Downloaded from www.sciencemag.org on March 13, 2015
By Cally Carswell
Foggy days are an increasingly rare sight in Los Angeles.
PHOTO: © SUPERSTOCK/CORBIS
combination of properties to keep the Higgs light. In supersymmetry that would happen “naturally,” as the effects of partnered particles on the Higgs mass would cancel because of the difference in their spins. Unfortunately for physicists, those superpartners didn’t show up in the LHC’s first run. So now researchers are focusing mainly on finding the “stop squark,” the superpartner of the top quark, the standard model particle that most influences the Higgs’s mass. Even those searches are looking a bit iffy, as the failure to see the stop so far shows that it must weigh more than 0.7 TeV, a value that strains the theory. Still, Sanjay Padhi of the University of California, San Diego, says he’s optimistic. “I will start to worry if the stop is not found up to 1.5 TeV,” says Padhi, who works on CMS, one of the detectors that discovered the Higgs. Interest is also rising in trying to blast out particles of dark matter—the mysterious stuff whose gravity binds the galaxies. Cosmological measurements show that it makes up 85% of all matter in the universe. “We know there is something beyond the Higgs,” says Stephanie Majewski, a physicist at the University of Oregon in Eugene who works on the ATLAS particle detector, which also discovered the Higgs. “We know that there is dark matter, and we ought to be able to produce it with the LHC.” The dark matter particles themselves would not be directly detectable. To deduce their presence, physicists will look for lopsided “mono-X” events: proton-proton collisions that send a standard model particle or a jet of them flying in one direction and nothing detectable going the opposite way—an absence that would reveal a hidden particle. But John Ellis, a theorist at King’s College London, cautions that dark matter particles could have different, more complicated signatures. If nothing new shows up in the next few years, people may drift away from the LHC, Pierini says. But Ellis says physicists have a good decade before they should worry. CERN plans to upgrade the LHC’s particle detectors in 2018 and the accelerator itself around 2022, to boost its intensity. A bigger concern, Pierini says, is that experimenters might inadvertently overlook a new effect. To keep the data rate manageable, physicists rely on computerized “triggers” to sift out the few encounters between countercirculating bunches of protons that contain interesting proton-proton collisions. The triggers toss data from all but a few of every 100,000 bunch crossings. “It’s really terrifying to think that there is something there but that we didn’t discover it because we just didn’t look for it,” Pierini says. “That’s what keeps me up at night.” ■
sciencemag.org SCIENCE
13 MARCH 2015 • VOL 347 ISSUE 6227
Published by AAAS
PHOTO: SUZANNE BOTT
fog. In contrast, the San Diego area saw less dramatic declines, and Santa Barbara saw little change. To explain the variability, Williams tried comparing the trends with land use data. “The scatterplot came out, and everything just lined up,” he recalls. The airports that experienced the greatest fog declines tended to sit within the landscapes that had undergone the most development since 1950. That urbanization led to a marked increase in nighttime air temperatures, a result of all that concrete and asphalt absorbing heat during the day and slowly radiating it after dark. The warmth pushed up the elevation at which air cools enough for water vapor to condense—effectively eliminating fog. Williams says this warming mechanism could eventually squeeze out stratus clouds, which form only below about 800 meters, especially in inland regions, where the ocean’s cooling effect is smaller. Indeed, in his study, though the lowest clouds changed most dramatically, overall cloud cover in the Los Angeles region declined as well. Such changes could have implications for both regional ecosystems and humans. Fog is likely a key source of water in the arid forests and chaparral that ring Los Angeles, notes Christopher Still of Oregon State University, Corvallis. Loss of the moisture could result in “a lot of plant mortality and … ecological change,” he says. And although clearer conditions could increase the region’s ability to produce solar energy, they might also bump up temperatures in existing urban “heat islands,” leading to greater energy use for cooling and raising health issues related to heat stress. What Williams’s study portends for global fog trends is less clear. He found, for example, that even as the cloud layer lifted inland, it slipped to lower altitudes off the California coast over the Channel Islands, increasing fog there. Without the urban heat island effect, he says, “this same trend might have been seen over L.A. and San Diego.” And how marine clouds might change in a warming world is murky. Rising sea surface temperatures would tend to reduce stratus cloud cover, notes Katinka Bellomo, a doctoral candidate at the University of Miami in Florida, who is using ship records to study clouds over the Pacific and Indian oceans. But climate models also project changes in the lower atmosphere that would increase the clouds. So far, she says, “we don’t know which one prevails.” In California, however, everyday concerns are often more parochial. When people learn she studies the clouds that cause May Gray and June Gloom, Schwartz says they often ask: “You’re trying to figure out how to get rid of them, right?” She politely tells them no. ■
The arches and statues of Hatra in northern Iraq stood for 2000 years, but now may be gone.
ARCHAEOLOGY
Militants leave trail of destruction at Iraqi sites The Islamic State group strikes one valuable archaeological site after another, destroying priceless ruins and artifacts By Andrew Lawler
T
he ancient city of Hatra fended off two Roman emperors and repulsed a ruler of Persia’s powerful Sassanid dynasty. But late last week, local people near the ornate ruins about 110 kilometers southwest of the Iraqi city of Mosul heard massive explosions that likely marked the demise of the 2000-year-old city and its spectacular, well-preserved sculptures and stone architecture. While inflicting misery on the people of northern Iraq, supporters of the Islamic State group have also attacked one ancient site after another in the past 2 weeks, systematically taking sledgehammers and drills to artifacts. Other reports say that the forces of the group, increasingly known by its Arabic acronym Daesh, are using bulldozers to demolish ancient buildings. By last week the toll included the statues in the Mosul Museum, the classical site of Hatra, and the ancient Assyrian capitals of Nineveh, Nimrud, and Khorsabad, famed for their massive protective deities in the form of humanheaded winged bulls. Assur, a 4500-year-old temple-studded Assyrian city where kings and queens were laid to rest for centuries, is likely the next target, say archaeologists, who are desperately trying to piece together the extent of the damage. The unprecedented wave of destruction has prompted a small protest march in Washington, D.C., as well as statements of
SCIENCE sciencemag.org
outrage from archaeologists and museum curators around the world. U.N. officials have said that the events constituted a war crime. “Those barbaric, criminal terrorists are trying to destroy the heritage of mankind and Iraq’s civilization,” said Iraqi Prime Minister Haider al-Abadi. He spoke during a ceremony on 28 February in which his government reopened Baghdad’s long-shuttered Iraq Museum as a way of reaffirming the importance of the country’s heritage. Outside experts feel the losses keenly, because northern Iraqi sites have been largely off-limits to study since the start of the first Gulf War a quarter-century ago. “Assyria was the first true empire in world history,” says Yale University Assyriologist Eckart Frahm. Its “scholarly exploration is far from complete.” For example, many of the inscriptions at Nimrud have yet to be properly documented, he says. Representatives and publications from the Islamic State group have said that statues and reliefs of animals and humans are anathema to their brand of Sunni Islam. “We were ordered by our prophet to take down idols and destroy them,” explained an unidentified Daesh representative in a video widely distributed earlier this month, which showed men pushing intricately carved statues off their plinths and smashing the remains with sledgehammers. Another video image showed a man using an electric drill to destroy the human face of a huge winged bull standing at a gate at Nineveh. 13 MARCH 2015 • VOL 347 ISSUE 6227
Published by AAAS
1185
1184
ATMOSPHERIC SCIENCE
California fogs are thinning Warming linked to urbanization prevents low clouds from forming, Los Angeles area study shows
F
or years, sun worshippers have flocked to southern California’s coast, only to be disappointed each spring when the weather turns drab and foggy, a phenomenon locals call “May Gray” and “June Gloom.” But the low-hanging marine clouds responsible for that gloom have declined dramatically over the past 60 years, a new study concludes. It fingers the growth of cities and their heat-retaining concrete as a prime cause. The research, recently published online in Geophysical Research Letters, offers insight into how increasing urbanization may erode coastal fog banks in the future, with potentially serious consequences for people and ecosystems. It’s “the first definitive look at how fog might change for a specific coastal region,” says Travis O’Brien, a research scientist at Lawrence Berkeley National Laboratory in California, who was not involved in the research. To understand how California’s coastal fog might be changing, some 6 years ago lead author Park Williams, now a bioclimatologist at Columbia University’s Lamont-Doherty Earth Observatory in Palisades, New York, began assembling data from 24 southern California airports, which keep hourly records of fog conditions. He hoped to identify key climate variables influencing fog, such as sea surface temperatures and wind patterns. He revisited the data for years, but was unable to
spot any notable trends. Last year, however, Rachel Schwartz, a Ph.D. candidate at the Scripps Institution of Oceanography in San Diego, California, sent Williams a study she was finishing. It showed that low clouds had declined slightly over the past 60 years from coastal California to Alaska. But fog had nearly disappeared at the Los Angeles and Long Beach airports over a similar period, earlier studies by another researcher concluded. Those contrasting results gave Williams an idea: Perhaps the low clouds had not disappeared, exactly, but gained height. He realized that he had lumped together two potentially distinct data sets on stratus clouds, which form between the cool sea surface and a warm, stable inversion. The clouds can form close to the ground, as fog, which tends to burn off by afternoon; they can also sit higher in the sky and linger all day. Reanalyzing his data, Williams saw—at last—some intriguing trends. The lowest tier of clouds, it turned out, was heavily influenced by land use—and changing more dramatically than the higher clouds. At some airports, fog was becoming a threatened species; at one strip in Ontario, California, the average height of the summer clouds lifted by 170 meters between 1950 and 2014. That amounted to an 87% decline in the lowest clouds; summer fog that once regularly cloaked nearby mountains in moisture now visits them rarely. Overall, the Los Angeles region showed a 64% reduction in
Downloaded from www.sciencemag.org on March 13, 2015
By Cally Carswell
Foggy days are an increasingly rare sight in Los Angeles.
PHOTO: © SUPERSTOCK/CORBIS
combination of properties to keep the Higgs light. In supersymmetry that would happen “naturally,” as the effects of partnered particles on the Higgs mass would cancel because of the difference in their spins. Unfortunately for physicists, those superpartners didn’t show up in the LHC’s first run. So now researchers are focusing mainly on finding the “stop squark,” the superpartner of the top quark, the standard model particle that most influences the Higgs’s mass. Even those searches are looking a bit iffy, as the failure to see the stop so far shows that it must weigh more than 0.7 TeV, a value that strains the theory. Still, Sanjay Padhi of the University of California, San Diego, says he’s optimistic. “I will start to worry if the stop is not found up to 1.5 TeV,” says Padhi, who works on CMS, one of the detectors that discovered the Higgs. Interest is also rising in trying to blast out particles of dark matter—the mysterious stuff whose gravity binds the galaxies. Cosmological measurements show that it makes up 85% of all matter in the universe. “We know there is something beyond the Higgs,” says Stephanie Majewski, a physicist at the University of Oregon in Eugene who works on the ATLAS particle detector, which also discovered the Higgs. “We know that there is dark matter, and we ought to be able to produce it with the LHC.” The dark matter particles themselves would not be directly detectable. To deduce their presence, physicists will look for lopsided “mono-X” events: proton-proton collisions that send a standard model particle or a jet of them flying in one direction and nothing detectable going the opposite way—an absence that would reveal a hidden particle. But John Ellis, a theorist at King’s College London, cautions that dark matter particles could have different, more complicated signatures. If nothing new shows up in the next few years, people may drift away from the LHC, Pierini says. But Ellis says physicists have a good decade before they should worry. CERN plans to upgrade the LHC’s particle detectors in 2018 and the accelerator itself around 2022, to boost its intensity. A bigger concern, Pierini says, is that experimenters might inadvertently overlook a new effect. To keep the data rate manageable, physicists rely on computerized “triggers” to sift out the few encounters between countercirculating bunches of protons that contain interesting proton-proton collisions. The triggers toss data from all but a few of every 100,000 bunch crossings. “It’s really terrifying to think that there is something there but that we didn’t discover it because we just didn’t look for it,” Pierini says. “That’s what keeps me up at night.” ■
sciencemag.org SCIENCE
13 MARCH 2015 • VOL 347 ISSUE 6227
Published by AAAS
PHOTO: SUZANNE BOTT
fog. In contrast, the San Diego area saw less dramatic declines, and Santa Barbara saw little change. To explain the variability, Williams tried comparing the trends with land use data. “The scatterplot came out, and everything just lined up,” he recalls. The airports that experienced the greatest fog declines tended to sit within the landscapes that had undergone the most development since 1950. That urbanization led to a marked increase in nighttime air temperatures, a result of all that concrete and asphalt absorbing heat during the day and slowly radiating it after dark. The warmth pushed up the elevation at which air cools enough for water vapor to condense—effectively eliminating fog. Williams says this warming mechanism could eventually squeeze out stratus clouds, which form only below about 800 meters, especially in inland regions, where the ocean’s cooling effect is smaller. Indeed, in his study, though the lowest clouds changed most dramatically, overall cloud cover in the Los Angeles region declined as well. Such changes could have implications for both regional ecosystems and humans. Fog is likely a key source of water in the arid forests and chaparral that ring Los Angeles, notes Christopher Still of Oregon State University, Corvallis. Loss of the moisture could result in “a lot of plant mortality and … ecological change,” he says. And although clearer conditions could increase the region’s ability to produce solar energy, they might also bump up temperatures in existing urban “heat islands,” leading to greater energy use for cooling and raising health issues related to heat stress. What Williams’s study portends for global fog trends is less clear. He found, for example, that even as the cloud layer lifted inland, it slipped to lower altitudes off the California coast over the Channel Islands, increasing fog there. Without the urban heat island effect, he says, “this same trend might have been seen over L.A. and San Diego.” And how marine clouds might change in a warming world is murky. Rising sea surface temperatures would tend to reduce stratus cloud cover, notes Katinka Bellomo, a doctoral candidate at the University of Miami in Florida, who is using ship records to study clouds over the Pacific and Indian oceans. But climate models also project changes in the lower atmosphere that would increase the clouds. So far, she says, “we don’t know which one prevails.” In California, however, everyday concerns are often more parochial. When people learn she studies the clouds that cause May Gray and June Gloom, Schwartz says they often ask: “You’re trying to figure out how to get rid of them, right?” She politely tells them no. ■
The arches and statues of Hatra in northern Iraq stood for 2000 years, but now may be gone.
ARCHAEOLOGY
Militants leave trail of destruction at Iraqi sites The Islamic State group strikes one valuable archaeological site after another, destroying priceless ruins and artifacts By Andrew Lawler
T
he ancient city of Hatra fended off two Roman emperors and repulsed a ruler of Persia’s powerful Sassanid dynasty. But late last week, local people near the ornate ruins about 110 kilometers southwest of the Iraqi city of Mosul heard massive explosions that likely marked the demise of the 2000-year-old city and its spectacular, well-preserved sculptures and stone architecture. While inflicting misery on the people of northern Iraq, supporters of the Islamic State group have also attacked one ancient site after another in the past 2 weeks, systematically taking sledgehammers and drills to artifacts. Other reports say that the forces of the group, increasingly known by its Arabic acronym Daesh, are using bulldozers to demolish ancient buildings. By last week the toll included the statues in the Mosul Museum, the classical site of Hatra, and the ancient Assyrian capitals of Nineveh, Nimrud, and Khorsabad, famed for their massive protective deities in the form of humanheaded winged bulls. Assur, a 4500-year-old temple-studded Assyrian city where kings and queens were laid to rest for centuries, is likely the next target, say archaeologists, who are desperately trying to piece together the extent of the damage. The unprecedented wave of destruction has prompted a small protest march in Washington, D.C., as well as statements of
SCIENCE sciencemag.org
outrage from archaeologists and museum curators around the world. U.N. officials have said that the events constituted a war crime. “Those barbaric, criminal terrorists are trying to destroy the heritage of mankind and Iraq’s civilization,” said Iraqi Prime Minister Haider al-Abadi. He spoke during a ceremony on 28 February in which his government reopened Baghdad’s long-shuttered Iraq Museum as a way of reaffirming the importance of the country’s heritage. Outside experts feel the losses keenly, because northern Iraqi sites have been largely off-limits to study since the start of the first Gulf War a quarter-century ago. “Assyria was the first true empire in world history,” says Yale University Assyriologist Eckart Frahm. Its “scholarly exploration is far from complete.” For example, many of the inscriptions at Nimrud have yet to be properly documented, he says. Representatives and publications from the Islamic State group have said that statues and reliefs of animals and humans are anathema to their brand of Sunni Islam. “We were ordered by our prophet to take down idols and destroy them,” explained an unidentified Daesh representative in a video widely distributed earlier this month, which showed men pushing intricately carved statues off their plinths and smashing the remains with sledgehammers. Another video image showed a man using an electric drill to destroy the human face of a huge winged bull standing at a gate at Nineveh. 13 MARCH 2015 • VOL 347 ISSUE 6227
Published by AAAS
1185
