L y aura un quiz sur le vocabulaire

Bradbury’s message has been greeted by many coral advocates as a welcome dose of realism. “Roger’s editorial is the most powerful piece of writing on coral reefs I’ve seen in a long time, maybe ever,” says marine biologist-turned-filmmaker Randy Olson. “Scientists have to maintain the public’s trust by being honest, and Roger tells the truth instead of clinging to false hope.”

If anything, Bradbury’s op-ed undersold the peril by omitting coral bleaching from the litany of threats. Bleaching is typically caused by increased water temperatures, which induce stressed corals to eject the symbiotic algae that provide nutrients when times are good. Without their algal partners, corals turn a ghostly white, and reefs that remain bleached for too long can perish. Mass bleaching events, such as the die-off that swept Southeast Asia in 2010, are almost certain to occur more frequently in coming years.

Like acidification, warming water is a diffuse danger inflicted by the worldwide burning of fossil fuels. But while carbon emissions represent the greatest existential hazard to corals, many reefs are, at least for now, more damaged by local pressures such as overfishing and agricultural runoff. In the minds of many scientists, the fate of reefs will be determined by whether solving these local, comparatively manageable problems can make corals more resilient against intractable global ones.

For example, studies have suggested that large populations of herbivores like parrotfish, which graze seaweed and so prevent reefs from being engulfed by vegetation, can help corals recover from damage. This revelation has led scientists to advocate for the creation of Marine Protected Areas (MPAs) to safeguard parrotfish from overfishing and, in turn, preserve corals.

But can algae-eating fish fortify reefs against rampant warming and acidification? Probably not: a 2012 study by a trio of American scientists indicated that protected areas haven’t saved reefs from die-offs caused by temperature spikes. “The majority of coral scientists think that creating MPAs will improve coral resilience, but a lot of science suggests that hasn’t worked,” says John Bruno, a marine ecologist at the University of North Carolina and one of the study’s authors.

If interventions such as MPAs won’t save corals from runaway carbon, is there any hope that corals will save themselves? Certain species appear to be capable of adjusting to heat stress, and some, like the Northern Star Coral, can increase the pH of their calcifying fluid – the substance they excrete to form skeletons – under acidic conditions. As researchers wrote in Science in 2011, studies that forecast irreversible demise “may not adequately take account of reef organisms’ capacity for coping with stress and their potential for adaptation.”

Yet relying on acclimation and evolution is foolhardy, as the slow growth rates of many species impede rapid adaptation. “Corals can do some adapting, but the change that’s coming down the road is too great for them to handle,” says Doug Fenner, a reef ecologist at the Department of Marine and Wildlife Resources in American Samoa. “They’re pretty sensitive little animals.”

Coral scientists are unanimous on one point: if humans don’t cease pumping copious amounts of carbon dioxide into the atmosphere, reefs will eventually perish. “I’ve seen reefs that were destroyed by hurricanes bounce back in a decade,” says Fenner, “so I’m convinced that preventing local abuses can buy us some time. But if we don’t reduce CO2, we’re in deep trouble.” According to a 2007 study, reefs begin to erode faster than they grow when atmospheric CO2 exceeds 450 parts per million; our atmosphere already holds 396 ppm, and emissions show no signs of slowing.

Of course, just because we are on pace to turn oceans into hot, acidic dead zones does not mean that we necessarily will. Corals are only damned if civilization fails to stem the CO2 tide, and while Bradbury considers failure a fait accompli, not everyone agrees. “If we can get a handle on greenhouse gas emissions, corals have a chance,” says Bruno, who, it is worth noting, has been described as a pathological optimist. “I don’t think all reefs will die as soon as we cross, say, 400 ppm. I think we have some wiggle room.”

But Bruno’s if is a huge one, and ultimately, whether you think corals are “doomed” comes down to whether you believe society can completely transforming itself in the proximate future. On that point, Randy Olson is pessimistic. “Imagine a truck approaching a cliff at 100 miles per hour,” he says. “Sure, the driver could wake up and slam on the brakes, but that’s not likely.”

Coral’s destiny, like that of so many natural and human systems, is inseparably hitched to the trajectory of climate change. The rest of it – establishing MPAs, mitigating local pollution, praying for evolution to intervene – represents, in all likelihood, a collection of stall tactics that, if we’re extremely proactive and fortunate, will stave off extinction until we’re able to muster the political will to cut carbon. “We know what we need to do, and it’s pretty simple,” says Fenner. “Then again, our society has lots of fixable problems that we never manage to fix.”

By James Macintyre Wednesday, 19 March 2008 The Independent

Arthur C Clarke: Author of 2001: A Space Odyssey

Arthur C Clarke, the science fiction author of over a hundred books including 2001: A Space Odyssey, has died in Sri Lanka at the age of 90.

The author, who is credited with acting as a bridge between science and the arts, died after suffering breathing problems, an aide said last night.

Clarke, whose grounding in science allowed his fiction to act as the forerunner to real inventions, predicted as early as 1945 that satellites would one day broadcast TV images around the world. Geosynchronous orbits, which keep satellites in a fixed position relative to the ground, are known as Clarke orbits.

Born in Minehead, Somerset, in 1917, Clarke moved to London in 1936 and pursued his early passion for space science by joining the British Interplanetary Society. He also began to contribute to the BIS Bulletin and to write science fiction.

After the outbreak of war in 1939, he joined the RAF, becoming an officer in charge of pioneering radar equipment. His only non-science-fiction novel, Glide Path, was based on his role in the military. But it was for 2001: A Space Odyssey that he was most famous, published in 1968 while the author collaborated with Stanley Kubrick on the film by the same name.

Clarke moved to Sri Lanka in 1956, attracted by marine diving which he said was as close as he could get to the weightlessness of space. He was knighted in 2000.

The astronomer Sir Patrick Moore last night described his friend Clarke as, "a great visionary, a brilliant science fiction writer and a great forecaster ... he said there would be a man on the moon by 1970 – while I said 1980 – and he was right."

This was evident at this time by his increasing belief in the use of communications to bring mankind together in what he called the "global village". His lifetime thoughts on this were gathered in 1992 into a collection of ideas and idealistic possible futures published under the title How the World was One: Beyond the Global Village, a dream that satellite communications would promote understanding and worldwide peace. By this time, however, it was clear that, as with any other technology, the effect of communication satellites depends entirely on their manner of use. The coverage of the Falklands campaign of 1982 and Operation Desert Storm, the American-led liberation of Kuwait from Iraq of 1990-91, showed clearly that global TV, rather than bringing mankind together in peace, can transform the horror of war into exciting and technically interesting family entertainment. It was never evident that this reality soured the dreams that had driven Clarke for eight decades, for he never lost either his smile or his enthusiasm. Born in Minehead, Somerset, during the final appalling battles of the first world war, in which his father suffered injuries that brought him to an early death 13 years later, Clarke went to Huish's grammar school, Taunton, and, at 19, into the civil service in London. His father was a telephone engineer who, disastrously, turned to farming after the war because of lung damage, and his mother Nora (Willis) was formerly a telegraphist. His was a communications family. Like many schoolboys at this time, Clarke became fascinated by American science-fiction magazines ,which reached Britain in bulk, probably as scrap-paper ballast in returning cargo ships. But as Clarke later wrote, the turning point of his life was the discovery, shortly before his father died, of W Olaf Stapleton's book Last and First Men. Its imagination, timescale of billions of years and grand perception of the scale of the universe, provided a cosmic framework large enough to set Clarke's imagination free. He began writing science fiction. At 17 he joined the British Interplanetary Society, an organisation then widely regarded as crackpot, but of which he was later to be treasurer and, eventually, chairman. In the civil service his mathematical ability took him into the audit branch. But, after the outbreak of the second world war, he opted to join the RAF where, via electronics training, he became an instructor at radio school. Finally he went to work on the development and proving of American ground control approach - talk-down - radar at Davidstow Moor in north Cornwall, a system which pilots never liked because it robbed them of control until the last moments.

The head of the US team was Nobel-prizewinning physicist Luis W Alvarez - the first high-level scientist with whom Clarke had worked. As he described obliquely in his book Glide Path (1963), his only non-science fiction novel, this period shaped his decision to turn to science. In 1945 he published his famous pioneering paper on the possibility and technical potential of geosynchronous satellite orbits in global and interplanetary communications. He went on to gain a first in physics and mathematics at King's College London, and then a postgraduate degree in astronomy. The course was so boring that he became assistant editor on Science Abstracts, so that he would have time to think and to write.

The rest is almost a legend of our time. In 1953, on a US tour and with success already evident, he had a whirlwind romance with Marilyn Mayfield, a very young and beautiful divorcee who described the then bearded and buccaneering Clarke as her own Errol Flynn. A decade later, as Clarke chose the Sri Lankan culture as his working environment, the marriage was dissolved. Clarke's energy and momentum was at its height, taking him to the depths of the Indian Ocean and to every forum in the world where missiles and spaceflight were an issue. Clarke unwaveringly spoke for collaboration and peace. His last years were, increasingly, limited: post-polio syndrome left him confined to his wheelchair, and much of his public contact with the wider world was by telephone and then videolink. He was often - almost always by television link - one of the celebrities exploited by Nasa and other agencies to mark great moments in the exploration of space. But he remained unsentimental, and with a cheerful capacity for sending himself up: having lent his name to books and television programmes that explored the unlikely, the downright improbable and the decidedly dotty end of New Age speculation, he was once asked for his views on corn circles, those unexpected patterns that appeared suddenly, like eczema, in the wheat and barley fields of southern England, to be interpreted by New Age enthusiasts as messages from alien civilizations. "I do have a theory," he volunteered at a Science Museum press conference, on one of his rare visits. "They were made by half-witted extraterrestrials." His confinement and his age seemed not to trouble him, but in 1998 a British newspaper printed claims that Sir Arthur - his knighthood had just been announced - had been involved in sexual predation upon the young. He refused to accept his honour until the Sri Lankan authorities had investigated, and cleared his name. His knighthood was then awarded by Prince Charles on a visit to Sri Lanka in 2000. Apart from his huge output of fiction and scientific books, Clarke left us his Three Laws. These are touched by the kind of eternal practicality which make his science fiction so effective and reveal his inner convictions:

1. When a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong.
2. The limits of the possible can only be found by going beyond them into the impossible.
3. Any sufficiently advanced technology may, at first, be indistinguishable from magic.

Certainly, Clarke's imagination was magical, carrying him beyond the limits of possibility: his greatness was and remains that, from his almost Olympian heights, he could see more than ordinary men will ever see. Moreover, he possessed the power to carry anyone who wished to join him on these great heights of mystery and clarity. If the world believes the clarity to be deceptive, it is not the fault of Arthur C Clarke

John Clute

By Patricia Sullivan

Arthur C. Clarke, 90, the world-famous science-fiction writer, futurist and unofficial poet laureate of the space age, died of a respiratory ailment March 18 at his home in Colombo, Sri Lanka.

Mr. Clarke co-wrote, with director Stanley Kubrick, the screenplay for "2001: A Space Odyssey," which is regarded by many as one of the most important science fiction films made. A prolific writer, with more than 100 published books, he was praised for his ability to foresee the possibilities of human innovation and explain them to non-scientific readers.

The most famous example is from 1945, when he first proposed the idea of communications satellites that could be based in geostationary orbits, which keep satellites in a fixed position relative to the ground.

Some scoffed, but the idea was proved almost a generation later with the launch of Early Bird, the first of the commercial satellites that provide global communications networks for telephone, television and high-speed digital communication. The orbit is now named Clarke Orbit by the International Astronomical Union.

"He had influenced the world in the best way possible," writer Ray Bradbury said in Neil McAleer's 1992 book "Arthur C. Clarke: The Authorized Biography." "Arthur's ideas have sent silent engines into space to speak in tongues. His fabulous communications satellite ricocheted about in his head long before it leaped over the mountains and flatlands of the Earth."

In addition to his books, he wrote more than 1,000 short stories and essays. One of his short stories, "Dial F for Frankenstein" (1964), inspired British computer scientist Tim Berners-Lee to invent the World Wide Web in 1989.

Mr. Clarke also popularized the idea of a space elevator as an energy-efficient alternative to rockets. Conceived by a Russian engineer in 1960 and re-invented at least four times in the next decades, Mr. Clarke's inclusion of the idea in a 1979 novel brought it to popular attention and helped launch a new field of study. He told New Scientist magazine last year that it would be built "50 years after everyone stops laughing."

But it was his collaboration with Kubrick in the 1968 film that made him internationally famous. The screenplay for "2001: A Space Odyssey" was based on Mr. Clarke's 1951 short story "The Sentinel," and Mr. Clarke simultaneously wrote the companion novel, which was released three months after the film and was believed by many to be a more detailed explanation of the ideas in the film.

Mr. Clarke's work inspired the names of spacecraft, an asteroid and a species of dinosaur. He joined American broadcaster Walter Cronkite as a commentator on the Apollo moonshots in the late 1960s. Two television series in the 1980s spread his ideas around the world.

He was knighted in 1998, nominated for the Nobel Peace Prize in 1994 and received the Franklin Institute gold medal, the United Nations Educational, Scientific and Cultural Organization-Kalinga Prize and other honors.

Mr. Clarke, a resident of Sri Lanka since 1956, worked with Jacques Cousteau and others to help perfect scuba equipment. He moved to the country, then known as Ceylon, to open a dive shop and explore the undersea world. Disabled by post-polio syndrome, the lingering effects of a disease that had paralyzed him for two months in 1959, Mr. Clarke said diving was as close as he could get to the weightless feeling of space.

"I'm perfectly operational underwater," he once said.

His dive shop was destroyed in the 2004 tsunami.

Born Dec. 17, 1917, in Minehead, Somerset, England, he was the son of a postal service engineer turned farmer and a post office telegrapher. He became addicted to science fiction at 11.

In 1936, he moved to London and joined the British Interplanetary Society and began writing science fiction. After enlisting in the Royal Air Force in 1941, he became a radar instructor and participated in the development of ground-controlled landings of aircraft under zero-visibility conditions. That experience proved the inspiration for his only non-science-fiction novel, "Glide Path."

It is also where, in 1945, he wrote an RAF memo about satellites. He later revised it and submitted it as "Extra-Terrestrial Relays" to Wireless World, which almost rejected it as too far-fetched. He was wrong about some things: He expected that three satellites would take care of the world's communication needs and that each would require a crew in residence.

After World War II, Mr. Clarke obtained a bachelor of science degree in physics and mathematics at King's College, London.

In 1954, Mr. Clarke wrote to Harry Wexler, then chief of the Scientific Services Division at the U.S. Weather Bureau, about satellite applications for weather forecasting. From these discussions, a new branch of meteorology was born.

Mr. Clarke's marriage to Marilyn Mayfield ended in divorce. Survivors include a brother and sister, both of whom live in England.

According to a news release from the Arthur C. Clarke Foundation, Mr. Clarke reviewed the final manuscript of his latest science fiction novel, "The Last Theorem," a few days ago. It is scheduled to be published later this year.

Although he rarely left Sri Lanka, he kept in touch with the rest of the world by using the satellite communication he predicted so long ago. He told the Associated Press that he didn't regret never going into space because he had arranged to have the DNA from his hair sent into orbit.

"Some day, some super civilization may encounter this relic from the vanished species and I may exist in another time," he said.

In a 90th birthday video recorded in December, Mr. Clarke said he had only three last wishes: That someone find evidence of extraterrestrial life; that the world adopt clean energy sources; and that an end be found to the long civil war in Sri Lanka.

"I'm sometimes asked how I would like to be remembered. I've had a diverse career as a writer, underwater explorer, space promoter and science populariser," he said. "Of all these, I want to be remembered most as a writer -- one who entertained readers, and, hopefully, stretched their imagination as well."

© 2008 The Washington Post Company

• 
  05 December 2007
  
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  NewScientist.com news service
  
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  Andrew Robinson
  

"I BET Arthur has forgotten this," British astronomer Patrick Moore tells me before launching into a story about Arthur C. Clarke, his old friend from the heyday of the British Interplanetary Society. In those cold-war times, a group such as the BIS - which advocated space travel and collaboration with the Russians - was the object of official suspicion, not to mention derision from scientists working for the establishment. (In 1956, no less a figure than Richard Woolley, the UK's astronomer royal, asserted: "All this writing about going to the moon is utter bilge.")

Moore recalls that around 1950, Clarke went into a museum - it may have been London's Science Museum - carrying a suitcase. "Knowing that he was a member of the BIS, one of the attendant officers insisted on looking into the suitcase to make sure it didn't contain a bomb."

Clarke has indeed forgotten the suitcase incident when I mention it over lunch on the veranda of his house in Sri Lanka, where he has lived for almost half a century, and where I first met him in the 1980s. This is hardly surprising, given that he turns 90 on 16 December. His memory, he says ruefully, has undergone a "data dump", even if his mind ranges as swiftly and eclectically as ever. But he is curious to know what was in the suitcase. Perhaps, we speculate, it contained some futuristic, though no doubt technically sound, designs for a rocket put forward by the precocious enthusiasts of the BIS.

Clarke's fascination with rockets goes back to his teenage years in England, when he launched home-made ones from his mother's farm in his native Somerset. His father, a post office engineer, died when Arthur was 13, from the lingering effects of being gassed in the first world war. Space rockets became possible, at least technically, with the launch of Germany's V2 rocket during the second world war, when Clarke was serving in the Royal Air Force, working on radar. Looking back, that feels like the "Jurassic" period of his life, he says. Even the start of the space age 50 years ago is "sort of ancient history - the Battle of Hastings so far as I'm concerned".

By then he had fully embarked on his tireless advocacy of space travel in both fiction and non-fiction, through books such as The Sands of Mars, A Fall of Moondust, The Exploration of Space and Profiles of the Future. Nevertheless, he was amazed that the moon landing happened so soon, in 1969. He had not expected to see it in his lifetime. "And then I was also surprised, and disappointed, that it wasn't followed up. We abandoned space for decades." Clarke's screenplay and companion novel for the movie 2001: A Space Odyssey, made by Stanley Kubrick in 1968, had imagined the construction of a moon base in the 1990s.

He still expects the establishment of scientific bases and perhaps colonies on the moon and in other parts of the solar system by the end of the century. But will people go to live in these outposts and regard them as their home planets? They probably will, Clarke says, pointing out that this has already happened on Earth in very "improbable", inhospitable places. "With the technologies we have, or should have, I'd expect people to live, most certainly, on Mercury, Venus and Mars, the satellites of Jupiter and quite a few asteroids." As he once remarked, twisting Oscar Wilde: "We have to clean up the gutters in which we are now walking - but we must not lose sight of the stars."

There is an element of faith in Clarke's attitude to space, though not the religious type. His attitude is more like a boundless optimism in the power of intelligence. Such optimism underlies his best-known novels, Childhood's End, 2001 and Rendezvous with Rama. Kubrick, who tended to be sparing with his praise, once said of his collaborator: "Arthur somehow manages to capture the hopeless but admirable human desire to know things that can really never be known."

“Clarke has a boundless optimism in the power of intelligence”

This visionary hopefulness is Clarke's chief appeal to his legion of non-scientist admirers. These include Rupert Murdoch and Steven Spielberg, and a host of science fiction writers such as Ray Bradbury, Stephen Baxter and the late Gene Roddenberry, the brain behind the TV series Star Trek. Ronald Reagan was also an admirer, despite Clarke's opposition to his "Star Wars" strategic defence initiative in the 1980s.

Many scientists - and astronauts - go further in their admiration, respecting Clarke for his unique combination of scientific knowledge, intellectual originality and literary flair. J. B. S. Haldane, Wernher von Braun, Luis Alvarez, Isaac Asimov and Carl Sagan were all personal friends of Clarke, as well as fans of his writing. As a high-school student in the early 1950s, Sagan decided to become an astronomer after reading Interplanetary Flight, Clarke's first book.

Moore considers the greatest science fiction books to be Last and First Men and Star Maker by Olaf Stapledon, but "these were Stapledon's only two great books, which is why on balance I must make him number two to Arthur". Martin Rees, the UK's current astronomer royal, agrees: "The geostationary satellite idea - just one of his far-sighted concepts - was 'rediscovered' after Sputnik, and soon became reality. But his other concepts still lie far ahead - some, indeed, in a post-human future billions of years hence... Scientists can derive more benefit and stimulus from him than from routine science fact."

Clarke's influence on the development of satellites is profound. John Pierce and Harold Rosen, the two engineers principally responsible for the design of communications satellites in the 1960s, regarded him as the "father" of satellite communications on the strength of his technical article "Extra-terrestrial relays", published in Wireless World in late 1945 while its 27-year-old author was still in the RAF. This acknowledgement has now entered encyclopedias - much to the satisfaction of Clarke, who regards the article as "the most important thing I ever wrote", even above his novels. Though he has never been one to downplay his science fiction, or indeed any of his achievements - witness his annual self-styled "Egogram" newsletter to friends and acquaintances - Clarke is probably right about his "comsat" idea: it will be his most enduring legacy.

He cannot recall exactly how the basic idea came to him, though he says it emerged from a combination of his family's connection with post office engineering, his passion for rockets and his work during the war on ground-controlled radar, later fictionalised in Glide Path. "While working on radar I remember thinking: could the beam be powerful enough not just to detect the other guy but also to shoot his plane down? Power-beaming was one of the ingredients in the comsat idea, I'm sure." But deferring to the engineers who made his 1945 concept a reality, he prefers to style himself not as the father of satellite communication but as its godfather. "If I hadn't written that paper in October 1945, 10 people would have done it the next year."

“He styles himself as godfather to satellite communications”

While this may be uncharacteristically modest, it is true that a similar idea had been discussed by others before 1945, and that Pierce's first paper on the subject was published a decade later without knowledge of Clarke's pioneering proposal.

One irony of all this is that Clarke now depends on comsats, since he can no longer travel far due to the debilitating effects of post-polio syndrome. For years, he has sent video messages via satellite to conferences across the globe - most recently on the 60th anniversary of his 1945 article. Yet as a "failed recluse" addicted to email, he is ambivalent about the benefits of everyone being able to communicate instantaneously. "It's the fractal future," he says. "Although everybody is ultimately connected to everybody else, the branches of the fractal universe are so many orders of magnitude away from each other that really nobody knows anyone else. We will have no common universe of discourse. You and I can talk together because we know when I mention poets and so on who they are. But in another generation this sort of conversation may be impossible because everyone will have an enormously wide but shallow background of experience that overlaps by only a few per cent."

Prescient though many of his ideas are, Clarke is aware he is as vulnerable as anyone to what he calls "the perils of prophecy". In his 1945 article he assumed that the three geostationary space satellites required for a global communications service would need a crew, with supplies ferried up by a "regular rocket service". The radar he was in charge of in 1945 contained over 1000 vacuum tubes, at least one of which burned out every day, so it seemed inconceivable to him that any complex piece of electronic equipment could function in space without on-the-spot engineers. "Well, along came the transistor, and then the microchip. So within a decade, electronic equipment that was once as large as a house could be put in a hatbox."

The other major scientific idea that makes him proud is the space elevator - an energy-efficient alternative to rockets, which envisions carbon-fibre ribbons stretching from the Earth's surface to a geostationary orbital station some 36,000 kilometres up. Unlike comsats, Clarke didn't invent the space elevator; it was conceived in 1960 by Russian engineer Yuri Artsutanov (who called it a "heavenly funicular"). It was independently reinvented at least four times by American scientists in the 1960s and 1970s. But it was Clarke who brought it to popular attention with his 1979 novel The Fountains of Paradise, in which the elevator rises from the summit of a sacred mountain on an equatorial island remarkably similar to his adopted home. The novel, and his subsequent technical writing on the elevator, helped to spawn a large new field of study. There is now an annual competition to encourage the development of a workable space elevator - the Spaceward Games, organised by the Spaceward Foundation and NASA's Centennial Challenges programme.

It may sound like outlandish fantasy, but in 1945 so did communication satellites and landing on the moon. He doesn't always get it right, however: in 1999 he predicted the last coal mine would close in 2006. Nevertheless, Clarke maintains that the space elevator will be built "50 years after everyone stops laughing" - probably sometime this century. Whenever this fabulous structure is finally constructed, some aspect of it will surely be named after him. Sir Arthur - who already has a geostationary orbit and an asteroid for namesakes - would expect no less.

Andrew Robinson is the author of The Story of Measurement (Thames & Hudson, 2007) and a visiting fellow of Wolfson College, University of Cambridge

From issue 2632 of New Scientist magazine, 05 December 2007, page 58-60

By Kwame Anthony Appiah Sunday, September 26, 2010; B01 The Washington Post

Once, pretty much everywhere, beating your wife and children was regarded as a father's duty, homosexuality was a hanging offense, and waterboarding was approved -- in fact, invented -- by the Catholic Church. Through the middle of the 19th century, the United States and other nations in the Americas condoned plantation slavery. Many of our grandparents were born in states where women were forbidden to vote. And well into the 20th century, lynch mobs in this country stripped, tortured, hanged and burned human beings at picnics.

Looking back at such horrors, it is easy to ask: What were people thinking?

Yet, the chances are that our own descendants will ask the same question, with the same incomprehension, about some of our practices today.

Is there a way to guess which ones? After all, not every disputed institution or practice is destined to be discredited. And it can be hard to distinguish in real time between movements, such as abolition, that will come to represent moral common sense and those, such as prohibition, that will come to seem quaint or misguided. Recall the book-burners of Boston's old Watch and Ward Society or the organizations for the suppression of vice, with their crusades against claret, contraceptives and sexually candid novels.

Still, a look at the past suggests three signs that a particular practice is destined for future condemnation.

First, people have already heard the arguments against the practice. The case against slavery didn't emerge in a blinding moment of moral clarity, for instance; it had been around for centuries.

Second, defenders of the custom tend not to offer moral counterarguments but instead invoke tradition, human nature or necessity. (As in, "We've always had slaves, and how could we grow cotton without them?")

And third, supporters engage in what one might call strategic ignorance, avoiding truths that might force them to face the evils in which they're complicit. Those who ate the sugar or wore the cotton that the slaves grew simply didn't think about what made those goods possible. That's why abolitionists sought to direct attention toward the conditions of the Middle Passage, through detailed illustrations of slave ships and horrifying stories of the suffering below decks.

With these signs in mind, here are four contenders for future moral condemnation.