TORNADO TERROR 

2011 is already the deadliest U.S. tornado season since 1953 — with 481 deaths confirmed so far, including at least 116 from Sunday's monster EF-4 in Joplin, Mo. — but it's still far from over, the National Weather Service warns. As rescue crews continue digging through the rubble in Joplin, forecasters say more strong tornadoes are "likely" to form in the Midwest today, especially between 4 p.m. and midnight. The storm system is expected to develop over Oklahoma, Kansas and north Texas this afternoon, then move east toward Missouri and Illinois tonight and into Wednesday morning. AccuWeather is predicting "50 or more tornado reports," adding that the twisters will potentially be long-lived and long-tracked, "even more so than the tornado that destroyed Joplin."

The year is less than half over, yet the number of U.S. tornado fatalities is already eight times the annual average, CNN reports. Improved technology for storm tracking has helped cut that average from around 200 down to 55 per year in recent decades, but 2011 is already rivaling the carnage of some pre-radar tornado seasons — and experts are left scratching their heads. "That's the question of 2011," says Bob Henson of the University Corporation for Atmospheric Research. "Why have so many people died in these tornadoes? That's the open question. It's partly because of the strength of these tornadoes. Also because they've hit populated areas." The NWS issued a tornado watch for Joplin at 1:40 p.m. Sunday, and upgraded to a tornado warning 24 minutes before the twister touched down, but NWS Director Jack Hayes said Monday that more could have been done. "We need to ask ourselves, what can we do to protect Americans?" he said. "I have to say, it's not enough. We have to do more." TIME's Jeffrey Kluger also suggests the sheer number of tornadoes this year may have desensitized some people to the danger, preventing them from taking shelter quickly enough. "The sirens always go off, so no one thought anything of it," says Joplin resident Alexa Wattelet. "Where we were, nobody really seemed like they were in much of a shock." Ultimately, the reason so many tornadoes are forming this year is a low-slung jet stream fueled by La Niña, Reuters reports, which is causing moisture from the Gulf of Mexico to collide with cooler Arctic air right above the central U.S.

The Joplin tornado was also "rain-wrapped," meaning it was cloaked by rainfall and thus difficult to see. Any tornadoes that form in the Midwest today and Wednesday will likely occur under similar conditions, the NWS warns, so residents should be prepared to seek shelter even if they never actually see a funnel cloud. Still, as CNN meteorologist Chad Myers points out, sometimes a tornado is just too powerful for anyone to survive, regardless of preparation. "Some tornadoes, you just can't survive them. They're just too big," he says. "And that is not to scare anyone. But the people that did it right are not to blame."

(Sources: CNN, Wall Street Journal, AccuWeather, Associated Press, Reuters)

VINE OF THE TIMES 

Trees were supposed to save us from global warming — or at least help us slow down the process — but now there appears to be a double agent at work, taking down trees from within the forest canopy. As the Science Times reports, a type of vine called a liana is booming in tropical forests across Central and South America, threatening to overtake the towering trees that act as "carbon sinks," or absorbers of climate-altering carbon dioxide. And while it's not entirely clear why lianas are suddenly thriving, some scientists blame the same phenomenon the vines help support: climate change.

"Lianas are increasing in tropical forests, no doubt about it," says Stefan Schnitzer, a biologist and liana expert at the Smithsonian Tropical Research Institute. "But what's most important is that they are increasing relative to trees." With lianas growing faster than their hosts, they've begun choking out the trees' ability to soak up CO2, allowing more of the heat-trapping gas to collect in the atmosphere. "Tropical forests store around one-third of the terrestrial carbon on the planet," Schnitzer says, "so big changes in tropical forests will mean a huge change to the global carbon cycle." In some areas, about 75 percent of large trees have lianas infesting their crowns, the Times reports, an increase of 57 percent since 1980. "Almost everywhere he's looked, or other people have looked, they've found essentially the same pattern," a fellow liana researcher says of Schnitzer.

Lianas aren't completely useless, of course — they're a key food source for animals during dry seasons, and, like all plants, they also absorb some CO2. But they absorb much less than trees do, and since they outcompete other plants for soil nutrients, water and light, they can stunt the growth of their fellow vegetation, eventually killing it. Experts aren't sure why lianas are seemingly waging war on tropical trees, but there are some theories, the Times notes. The parasitic vines may be better able to use all the extra CO2 in the air, despite absorbing less of it, making them part of a climate change feedback loop. They're also extremely effective at pulling water from the ground, and since they grow during the dry season — when trees are already weak — they're essentially kicking trees when they're down. "They're like straws," Schnitzer says. "They're growing when trees are starting to shut down. It's a water-based competitive advantage."

(Source: New York Times)

MORE MELTDOWNS 

Two more reactors at Japan's crisis-stricken Fukushima Daiichi nuclear plant likely suffered meltdowns shortly after the March 11 earthquake and tsunami, the plant's operator admitted today, raising the number of acknowledged meltdowns to three. Tokyo Electric Power Co. had previously only confirmed a meltdown at the No. 1 reactor, although the Japanese government and outside experts had already said fuel rods at reactors No. 2 and No. 3 probably also melted early in the crisis. TEPCO's announcement came as the International Atomic Energy Agency began a two-week investigation at the plant, in preparation for an accident report to be presented to the U.N. on June 20.

All three meltdowns took place within days of the plant being flooded by sea water from the tsunami, and TEPCO says most of the melted fuel in all three reactors is now submerged and doesn't threaten to magnify the already-dangerous situation. "It is unlikely that the meltdowns will worsen the crisis because the melted fuel is covered in water," TEPCO spokesman Takeo Iwamoto tells the Guardian. As Sophia University political science professor Koichi Nakano adds, TEPCO may be revealing the additional meltdowns now because anxiety about radiation exposure has calmed in recent weeks. "In the early stages of the crisis TEPCO may have wanted to avoid panic," Nakano says. "Now people are used to the situation … nothing is resolved, but normal business has resumed in places like Tokyo." TEPCO also might have felt pressured to make the admission before it was revealed by IAEA inspectors, the Guardian points out, or by a newly appointed government investigator.

Meanwhile, the company is still insisting that Fukushima Daiichi's reactors were knocked out by the tsunami, not the earthquake, since the latter scenario would raise doubts about its claims the plant could withstand even powerful seismic waves. "We don't think the quake affected the important parts of the plant, such as its cooling capacity," adds Hidehiko Nishiyama, a spokesman for Japan's Nuclear and Industrial Safety Agency. But Nakano tells Reuters that TEPCO and NISA may both be downplaying the earthquake's effects in hopes of dispelling broad fears about nuclear safety. "It could very well be that TEPCO is rushing to conclude that the tsunami is to blame to prevent further questions and give more momentum to the nuclear camp," he says. "It's not just TEPCO, it's the whole nuclear industry, maybe business circles as a whole. It's highly political."

(Sources: Guardian, Reuters)

BEE MINUS 

American honeybees are still dying in droves, according to a newly released annual survey of colony-collapse disorder, or CCD. Conducted by the U.S. Department of Agriculture and the Apiary Inspectors of America, the bee census finds a mix of good and bad news: CCD is still mysteriously killing off large numbers of honeybees, but the death rate doesn't seem to be increasing from previous years. 

"The lack of increase in losses is marginally encouraging in the sense that the problem does not appear to be getting worse for honeybees and beekeepers," says Jeff Pettis, an entomologist with USDA's Agricultural Research Service and a co-author of the new study. "But continued losses of this size put tremendous pressure on the economic sustainability of commercial beekeeping." Total losses from managed honeybee colonies across the U.S. were 30 percent from all causes for the winter of 2010-2011, according to the survey, a similar percentage from past years. Losses were 34 percent for 2009-'10, 29 percent for 2008-'09, 36 percent for 2007-'08 and 32 percent for 2006-'07. On average, U.S. beekeepers tell the USDA they believe losses of up to 13 percent would be acceptable, but 61 percent of responding beekeepers report suffering losses greater than that amount.

The cause of CCD has yet to be proven, although there are a variety of theories, including the widespread use of neonicotinoid insecticides, the proliferation of cellphone towers and infection by invasive mites. A total of 5,572 beekeepers responded to this year's survey, according to the USDA, representing more than 15 percent of the country's estimated 2.68 million bee colonies.

(Source: USDA Agricultural Research Service)

THIS DAY IN HISTORY

Civil War vet explores U.S. rivers, "An Inconvenient Truth" is released, and more.

Russell McLendon

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Photo (tornado damage in Joplin, Mo., on May 23): ZUMA Press

Photo (lianas growing over a tree): National Science Foundation

Photo (Fukushima Daiichi nuclear power plant): ZUMA Press

Photo (honeybee on a leaf): U.S. Department of Agriculture

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