Nature: Nearly half of Antarctica’s ice shelves—the portions of the ice sheet that extend over the ocean—are thinning due to warming ocean currents, according to new monitoring data and computer modeling. In fact, some ice sheets are losing more ice from such basal melting than from the calving—or breaking off—of icebergs, once thought to be the primary factor in ice-shelf dynamics. Eric Rignot of the University of California, Irvine, and colleagues, whose paper has been published in Science, also found that about half of the total meltwater comes from just 10 small ice shelves along the southeast Pacific coastline. Despite those losses, other ice shelves are thickening or maintaining equilibrium. Rignot and coworkers’ findings point up the difficulty of projecting long-term ice-sheet evolution because of the many factors involved, including sea-floor topography and ocean circulation, which change over time.
Ars Technica: As global temperatures increase, sea levels are predicted to rise, more severe weather events could occur, and agriculture and animal habitats may be disrupted, all of which will cause problems for humans. In an effort to limit world temperature rise to no more than 2 °C by 2020, the International Energy Agency (IEA) has proposed a four-step plan of action: accelerate the phasing out of fossil fuels, limit the construction and use of the least efficient coal plants, capture more of the methane generated before it enters the atmosphere, and improve the efficiency of buildings, vehicles, and industrial processes. Despite the reasonableness of the proposal, similar efforts in the past have been met by opposition from countries and companies because of the initial costs and potential loss of income from not developing their fossil-fuel reserves.
New York Times: Surface temperatures have risen slower in the past 15 years than in the previous 20, but that hasn’t changed the longer-term warming trend. Why warming has slowed in the short term isn’t known, but several theories have been proposed, and they may all contribute. One theory is that much of the heat trapped by greenhouse gases is being absorbed by the deep oceans, possibly due to shifts in winds and currents. Another points to a similar slowdown between the 1950s and 1970s. That period of slower warming may have been caused by an increase in atmospheric pollution that reflected sunlight. And in the past few decades, China and other developing countries have massively increased air pollution. Despite the slowdown, and whatever its cause, most of the hottest years on record have occurred during this recent period of slower warming.
New Scientist: Hydraulic fracturing—commonly called fracking—is a technique for extracting oil and natural gas from underground rock layers by pumping in water mixed with sand and chemicals. Use of the technique has become more common, but has been criticized for increasing groundwater pollution and causing geologic instability. And in California, which is home to the Monterey Shale Formation, concerns have arisen over potential air pollution. The formation is estimated to hold 1900 million tons of recoverable oil—more than 2.5 times as much oil as in the fields of North Dakota that sparked a boom economy there. However, much of the field is located in densely populated Los Angeles County, which already has high levels of air pollution. A petition was presented to Governor Jerry Brown asking for a statewide ban on fracking, but a bill proposing a moratorium on fracking was recently defeated in the legislature.
Science News: As the climate warms, monsoons could become more severe, bringing fewer but heavier rainfalls. In a study published this week in the Proceedings of the National Academy of Sciences, Yemane Asmerom of the University of New Mexico and colleagues analyzed cave formations in the state’s Carlsbad Caverns and compared the data with that from other caves across the Northern Hemisphere. Caves contain clues to past precipitation because features such as stalagmites grow as water seeps into the cave, evaporates, and leaves behind dissolved minerals. What the researchers found was that over long time periods of decades and even centuries, warm weather makes monsoons wetter and cold weather makes them drier. However, because of regional differences such as the concentration of aerosols or types of land surface features, monsoon activity is much less predictable on shorter time scales.
Los Angeles Times: The Oklahoma City suburb of Moore has been hit by major tornadoes in 1999, 2003, and now 2013. Weather experts believe that the tornado strikes are just a case of statistical bad luck and that the town’s specific location does not make it especially prone to storm formation. However, the middle part of the US is called Tornado Alley because it is the meeting area of warm, humid air from the Gulf of Mexico to the south and cool, dry air from the Rocky Mountains to the west. The two masses of air create swirling winds that spawn massive supercell thunderstorms. On the day of the most recent tornado, a lot of warm, moist air lay near the ground, with a quick drop in temperature as altitude increased. And a nearby dissipating storm may have caused a surge of low-level air that fed the circulation driving the storm. The resulting storm developed incredibly quickly, with the supercell forming in 10 to 15 minutes. The tornado itself lasted for 50 minutes and traveled for 20 miles, whereas most tornadoes last less than 10 minutes. Weather scientists hope to use extensive radar measurements and other observational data to try to determine why the tornado formed so quickly.
Telegraph: A period of significant global cooling called the Younger Dryas, which occurred between 12 800 and 11 500 years ago may have been caused by a meteorite explosion and impact. James Wittke of Northern Arizona University and his colleagues examined carbon spherules from 18 archeological sites worldwide, dating to 12 800 years ago. They found that the spherules were formed by sediments melting at temperatures of 2200 °C. They compared them with similar spherules from volcanoes, lightning, and human sources and determined that the ones they found were caused by heat and shock waves from an object passing through and exploding in the atmosphere. They estimate that 10 million tons of the spherules were spread over an area of 49 million km2 as a result of the meteorite fragmentation. The dust and ash could have triggered the significant cooling that followed and that was partly responsible for the extinction of several species, including woolly mammoths, and for major changes in human behaviors.
BBC: When an underwater earthquake generates a tsunami, every second counts because it takes only a few minutes before a wall of water can hit a shoreline. The current early warning system for tsunamis relies on seismographs to measure Earth movement and hence calculate the amount of energy dissipated into wave energy, but the technique is not reliable. A team from the GFZ German Research Centre for Geosciences says that GPS sensors placed around the coastlines of vulnerable countries could make highly precise measurements of how underwater tremors shift the ground. In turn, the data could be used to reconstruct the source of the earthquake and calculate its magnitude. ”You can then predict the tsunami and see how high a wave could be expected, with some accuracy,” says Andreas Hoechner, one of the researchers.
NPR: What some consider to be the most important historical site in the US—Jamestown, Virginia—may disappear by the end of the century because of global warming. Jamestown, founded in 1607, was the first permanent English settlement in the Americas. Because it sits just above sea level, it is being threatened by the rising ocean, whose surface, climate scientists say, could swell by as much as 1 meter by 2100. The area has already suffered water damage: In 2003 Hurricane Isabel flooded Jamestown’s visitor center and glass factory, where present-day glassblowers replicate Old World techniques. The National Park Service is considering its options, which could involve levees and sea walls, all of which will be expensive. As many treasures there are still buried in the ground, archaeologists are debating whether to dig up everything while they still can.
Spectroscopy Now: In 1286 a storm washed a large part of the English town of Dunwich into the North Sea and deposited significant amounts of silt in the mouth of the Dunwich River. Over the next 200 years, further storms continued to silt up the harbor and eat away parts of the city until most of the inhabitants abandoned the area. In the half-millennium since, most of the rest of the city has been washed into the sea. David Sear of Southampton University and his colleagues used high-resolution acoustic imaging technology to map the city’s underwater remains. Primarily used for imaging shipwrecks, the acoustic imaging was necessary because of the generally muddy nature of the water in the area. The imaging revealed that the city covered 1.8 km2, almost the area of present-day London. The coastal erosion that Dunwich experienced was due to storms that occurred during a period of significant global climate change. A better understanding of erosion processes caused by storms may help countries and towns prepare for potential effects of rising oceans and changing weather patterns due to global warming.