Coming Soon: the Next Great FluEpidemic
The virus first came to officials’ attention in a bag of dead chickens.Early in March 1997, a farmer from Hong Kong’s New Territories carried them into theAgriculture and FisheriesDepartment laboratory. The final state of some birds was a hideous, bloody mush.Cultures of their organs revealed they had died of avian influenza, type H5N1. Influenza of the H5 subtype had never been known to infect humans.But in the next seven months, 18 Hong Kong residents fell ill with H5N1 and six dieD、
In lateDecember 1997, public health officials took a drastic step, ordering the slaughter of every chicken in every farm and marketplace in Hong Kong. The HSN1 virus seemed to disappear but for how long
The specter of the 1918 flu was raised by this new avian flu. The 1918 flu was one of the most changeable and resistant viruses known to man.After we’ve been infected with one strain, it can mutate and infect us again. We are only immune to flu strains our bodies have seen before.
A、flu can also "jump species" to an animal it has never infected before, once such a flu moves into humans, if it can "learn" to pass easily between them, it can spark a pandemic—a global outbreak.
Birds carry the flu virus in their intestines and excrete it in their feces. In all likelihood, shoppers who got sick with H5 touched surfaces contaminated with chicken feces. Humans, however, carry flu in their respiratory tracts and usually spread them in a cough or sneeze. Flu strains that travel this way are highly contagious.
The H5 virus in Hong Kong was different. It sickened very few, but killed a third of those infecteD、Most who got sick with H5 seemed to catch it directly from a bird they bought in a live-poultry market.
After the Hong Kong outbreak, flu experts feared that H5—already deadly to humans—might learn to move between humans as well as between birds. That "raises the specter of 1918", says NancyCox, chief of the InfluenzaBranch of the U. S.Centers forDiseaseControl and PreventionCDCP).
Geographic isolation was no protection during the 1918 pandemiC、In theAlaska Territory, the mortality rate in some villages was as high as 90 percent.All told, at least 500000Americans perisheD、It could happen again.
The virus that became the Spanish flu probably came from a birD、Avian-flu expertDr. Robert Webster of St. JudeChildren’s Research Hospital in Memphis, Tenn., believes the virus may have leapt straight from birds to humans, possibly a year to two before the pandemic began. Once lodged in human lungs, it quickly passed from person to person in a simple cough or sneeze. To avoid that grim possibility, here are three measures all nations need to take:
The first step is better surveillance. Most countries, though, don’t start tracking avian flu until after an epidemic kills their chickens. The United States dramatically increased its monitoring after a deadly outbreak in Pennsylvania in the early 1980s. The USDA、(United StatesDepartment ofAgriculture) provides diagnostic support. Some virologists recommend enhancing surveillance of swine flu too. The U. S. National Institutes of Health is beginning to study the issue.
Elsewhere, the coverage is not good enough, saysDr. W. Paul Glezen of theBaylorCollege of Medicine’s Influenza ResearchCenter. He namesAfrica and SouthAmerica as areas where the World Health Organizations net is incomplete.
Another important measure is producing more vaccines and flu shots. Only three of the 15 known influenza subtypes—H1, H2 and H3—have been found in people. Vaccines exist for each, and an H5 vaccine is now being developeD、Some experts believe that we should develop a vaccine for the other known subtypes as well.
Health authorities add that more people need flu shots now. We should manufacture 120 million doses a year

WATERAND、LIFE、ON MARS
1The presence or absence of water has a direct bearing on the possibility of life on other planets. In the nineteenth century, it was commonly accepted that life, perhaps even intelligent life, was widespread in the solar system, and Mars was an obvious target in the search for life. New photographic technology offered a way for astronomers to learn more about the red planet. In 1888, Italian astronomer Giovanni Schiaparelli produced images that showed a network of long, thin, dark lines crossing the surface of Mars. He called these features canali in Italian, which became "canals" or "channels" inEnglish. The strange appearance of the canals suggested to some scientists that they had been formed artificially rather than naturally. The mystery deepened when Schiaparelli observed that many of the canals in the photographs were actually double.
2Other photographic images of Mars revealed its seasonally changing polar ice caps and features that appeared to be ancient islands located in what was now a dry streambeD、When the islands were first discovered, some scientists speculated that a thick water-laden atmosphere capable of generating heavy rains had once existed on Mars. However, others remained unconvinced of the presence of water. Then, in 1963, a team of astronomers obtained a good photographic plate of the near-infrared spectrum of Mars. The photograph showed that, faintly but definitely, water vapor lines could be seen. This photograph established that there really was water on Mars, though the amount was very small. Today, the presence of water vapor in the Martian atmosphere is generally accepted, as is the belief that the atmosphere was once much denser than it is now, with a much greater abundance of water vapor.
3The surface of Mars is dry today, but it does contain significant amounts of ice and signs that liquid water once flowed over the planet.All of the locations where evidence of water has been found are ancient, probably formed very early in Martian history.Data transmitted from spacecraft on Mars in 2004 have revealed that water was once common across a vast region of the planet, possibly as shallow lakes or seas that dried out and then filled up again. There are signs that the wind blew debris around during dry stages. These seas and lakes extended across hundreds of thousands of square miles, creating habitable conditions during long stretches of time billions of years ago.
4 Evidence of water includes the presence of various minerals known as evaporates, deposits left behind when liquid water turns to vapor. Small areas of mineral deposits have been found in Valles Marineris, a huge hole on Mars that is larger than the GrandCanyon onEarth. The minerals there contain water, so they had to be formed in the presence of water. Geologic research has also turned up clay and gypsum deposits that were formed by water in the soil. Rocks that clearly formed in water extend throughout 300 meters of layered materials in several locations across the Martian plains. The layers were built up over time, which means water was present, at least temporarily, for extended periods on ancient Mars.
5 Besides the ice packs at Mars’s poles, astronomers have discovered a frozen sea near its equator. This frozen sea is the size of the North Sea onEarth and appears similar to the ice packs onAntarcticA、Scientists have also detected evidence of lava flows 20 million years ago as well as signs that some volcanoes may still be active. Several recently formed volcanic cones near Mars’s North Pole indicate that the planet’s core may interact with the surface, meaning there was both warmth and moisture in the recent pas-circumstances that might have supported life.
6Liquid water is the key ingredient for life as we know it. Of all the other planets in the solar system, Mars is most likeEarth. The fact th

Rising Sea Levels
Perhaps the most pervasive climatic effect of global warming is rapid escalation of ice melt. Mount Kilimanjaro inAfrica, portions of the SouthAmericanAndes, and the Himalayas will very likely lose most of their glacial ice within the next two decades, affecting local water resources. Glacial ice continues its retreat inAlaskA、NASA、scientists determined that Greenland’s ice sheet is thinning by about 1 m per year. The additional meltwater, especially from continental ice masses and glaciers, is adding to a rise in sea level worldwide. Satellite remote sensing is monitoring global sea level, sea ice, and continental ice. Worldwide measurements confirm that sea level rose during the last century.
Surrounding the margins ofAntarctica, and constituting about 11% of its surface area, are numerous ice shelves, especially where sheltering inlets or bays exist.Covering many thousands of square kilometers, these ice shelves extend over the sea while still attached to continental ice. The loss of these ice shelves does not significantly raise sea level, for they already displace seawater. The concern is for the possible surge of grounded continental ice that the ice shelves hold back from the seA、
Although ice shelves constantly break up to produce icebergs, some large sections have recently broken free. In 1998 an iceberg (150 km by 35 km) broke off the Ronne Ice Shelf, southeast of theAntarctic PeninsulA、In March 2000 an iceberg taggedB-15 broke off the Ross Ice Shelf (some 90° longitude west of theAntarctic Peninsula), measuring 300 km by 40 kin. Since 1993, six ice shelves have disintegrated inAntarcticA、About 8,000 km of ice shelf are gone, changing maps, freeing up islands to circumnavigation, and creating thousands of icebergs. The Larsen Ice Shelf, along the east coast of theAntarctic Peninsula, has been retreating slowly for years. Larsen-A、suddenly disintegrated in 1995. In only 35 days in early 2002, Larsen-B、collapsed into icebergs. This ice loss is likely a result of the 2.5℃ temperature increase in the region in the last 50 years. In response to the increasing warmth, theAntarctic Peninsula is sporting new vegetation growth, previously not seen there.
A、loss of polar ice mass, augmented by melting of alpine and mountain glaciers (which experienced more than a 30 % decrease in overall ice mass during the last century) will affect sea-level rise. The IPCC、assessment states that "between one-third to one-half of the existing mountain glacier mass could disappear over the next hundred years".Also, "there is conclusive evidence for a worldwide recession of mountain glaciers... This is among the clearest and best evidence for a change in energy balance at theEarth’s surface since the end of the 19th century. "
Sea-level rise must be expressed as a range of values that are under constant reassessment.
The 2001 IPCC、forecast for global mean sea-level rise this century, given regional variations, is from 0.11～0.88 m.
The median value of 0.48 m is two to four times the rate of previous increase. These increases would continue beyond 2100 even if greenhouse gas concentrations are stabilizeD、

The Scripps Institute of Oceanography in La Jolla,California, has kept ocean temperature records since 1916. Significant temperature increases are being recorded to depths of more than 300 m as ocean temperature records are set.Even the warming of the ocean itself will contribute about 25% of sea-level rise, simply because of thermal expansion of the water. In addition, any change in ocean temperature has a profound effect on weather

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