According to Bukovsky, his work could lead to advances in fertility treatment that would allow women to grow and store their own viable eggs, and delay having a family until an older age. The stem cells could also be used to rejuvenate aging ovaries, with the potential of delaying menopause for 10 to 12 years.

In the study, which appears in the journal Reproductive Biology and Endocrinology, Bukovsky’s team collected cells from the surface of ovaries in five women ages 39 to 52. They then tried different strategies to grow the cells in dishes over five to six days. The researchers found that cells grown in the presence of the growth-stimulating hormone estrogen transformed into large egglike cells, which later became mature human eggs capable of being fertilized.

Robert Winston, a fertility expert based at Hammersmith Hospital in London, said the achievement is highly important, if it has been proved to work: “If they’ve really done this, it would be extraordinary. There is such a shortage of eggs, it’s incredibly important.” Significantly, harvesting eggs from the outer surface of ovaries is a straightforward procedure, and can be done using a common flexible instrument called a laparoscope.

The use of stem cells to prolong the life of ovaries and so delay menopause is also a significant advance, Winston added. “There’ll be a demand for it, particularly from professional women who want to pursue their careers,” he said.

Bukovsky’s team is now planning to test whether the stem cells they collected from women’s ovaries can withstand being frozen. “Once we’ve frozen them, we’ll thaw them out and see if they still work. If we can preserve them effectively, women could have them stored for 20 years,” he said. If the next experiments are a success, thawed stem cells taken from a woman’s own ovaries could be transformed into fresh eggs in the lab whenever they were needed. “This could extend fertility to the age of 60,” Bukovsky said. Because the eggs are created just before use, they are less likely to be damaged or worn, as typically happens to eggs that remain in a woman’s ovaries for long periods of time.

Scientists also revealed Wednesday that they have uncovered a new clue to the mystery of implantation — the process by which an embryo becomes wedded to the womb. Implantation is the last step in the chain of events between fertilization and pregnancy, and one of the least understood. If an embryo does not properly attach itself to the wall of the womb, it cannot develop into a viable fetus. Scientists reported in the journal Nature Wednesday that they had identified a certain type of protein that appears to play a crucial role in implantation. The discovery may lead to treatments for some of the 20 percent of infertility cases that currently go unexplained.

The experiment took place a few months ago as part of a broader trial into what are known in the business as brain-computer interfaces. Although it is early days, aficionados of the technology see a world where brain implants return ability to those with disability, allowing them to control all manner of devices by thought alone. There are huge hurdles ahead. No one knows how much information we can usefully decipher from the electrical fizz of the brain’s 100 billion neurons. More important, scientists are still in the dark as to what effect, if any, long-term implants will have on the human brain, or how its circuitry will cope with the new tasks demanded of it.

Nagle got involved in the latest trial after hearing about John Donoghue, a professor of neuroscience at Brown University in Rhode Island, whose company Cyberkinetics has developed an implant called BrainGate. Under Donoghue’s instruction, Nagle was given a general anesthetic before a disk the size of a poker chip was cut from his skull. After making an incision in the brain’s protective membrane, a tiny array of 96 hair-thin electrodes, each protruding about a millimeter, was pressed onto the surface of his brain, just above a region of the sensory motor cortex that is home to the neuronal circuitry governing arm and hand movement. With the electrodes in position, the bony disk was replaced, leaving room for a tiny wire to connect the electrodes to a metal plate the size of a 10-pence piece that sits on Nagle’s head like a button.

To read brain signals from Nagle’s motor cortex, Donoghue’s researchers attach an amplifier to the metallic button on his head and run a cable to a computer. When he’s hooked up, the tiny voltages of the sparking neurons beneath the electrodes produce a series of brainwaves that dance on the computer screen.

Since having the electrodes implanted in June last year, Nagle has been test-driving the technology, seeing what he, and it, are capable of. “We’re evaluating his ability to do a whole range of things. We’ve hooked him to a computer that lets him turn a TV on and off, change channels and turn the volume up and down,” says Donoghue.

The success of the technology relies on being able to decipher accurately the electrical activity within Nagle’s brain and turn it into useful actions. The trials started tentatively. Nagle had been unable to move any of his limbs for nearly four years. The scientists had no idea how this would have affected the brain signals that normally control movement. Would they have fizzled out through lack of use, much as muscles waste away for those in the wheelchairs? “No one knew if it would work in someone with these injuries, but simply by asking him to imagine moving we got useful signals and it was amazing. I was overwhelmed by how beautifully the cells were still working,” says Donoghue.

Getting the signals is one thing; deciphering them is another. But Donoghue’s team found that some simple rules held — if the brain wanted to move the hand to the right, certain cells would fire a rapid series of impulses. If the brain was willing the hand to move left, the cells fired a different number of times. Other information, such as where the hand should end up, what trajectory it should take, and how quickly it should move, is also embedded in the electrical signals.

Part of the difficulty in reading brain signals is that while even a simple movement such as raising a hand requires electrical signals from many regions of the brain, the implanted electrodes pick up just a tiny fraction of those that fire. “We’re recording only a dozen or so, when a million might be active,” says Donoghue, who likens the process to dropping a microphone into a crowded room and trying to get the gist of all the conversations going on.

The limitations of taking signals from just a few active neurons have become apparent in the trial. Many of the tasks Nagle is given involve moving a cursor around a screen by thinking which way it should move. But the cursor jiggles, making it difficult to select icons on the screen with any precision. “We could smooth it out using software, but at the moment, we want to see if Matthew can learn to control the wobble,” says Donoghue, who is recruiting four other patients to complete the trial. “If he can do that, he could use computer software to answer e-mails, and if he can do that, he could be employed.”

Ultimately, Donoghue says there should be no need to connect cables to people’s heads to read their minds. Miniaturization should bring smaller devices that can be powered through unbroken skin and transmit signals wirelessly from the brain to a processor worn on a belt that triggers the intended device.

If all goes according to plan, Donoghue’s trial, designed to explore how well a variety of people can control different devices by the power of thought, will be completed in about 18 months. He’s not the only one keen to find out just how useful such devices could be. At Duke University in North Carolina, Miguel Nicolelis is in the final stages of getting permission to fit 16 quadriplegic patients — half in the United States, half in Brazil — with brain implants for a period of 30 days. Initially the trial will look at whether the patients’ brains still produce useful motor signals. “Then, we want to see if these patients can control a robotic arm that can reach and grab objects, and how well their brains get used to it,” says Nicolelis.

In previous studies, his team showed that when monkeys had their brains hooked up to robotic arms, they assimilated the arm, effectively making it their own. “Their brains actually incorporated the robotic arm by dedicating neuronal space to it. We want to see if the same thing happens in humans,” he adds.

For all the promise brain implants hold, there are some who believe they are not the best bet for many patients. Implants suffer from a number of drawbacks, the first being that they demand invasive surgery, with attendant risks. Second, implanted electrodes cause at least some inflammation of the brain tissues they push into. As well as obvious medical concerns, if the inflammation is significant, it can smother any signals the electrodes might pick up.

“Every one you put in gives some inflammation, but it’s minor. We’re still working on making electrodes more biocompatible, but we’ve got monkeys who have so far survived for nearly five years with implants and they are fine,” says Nicolelis. “The thing is, to do what we want to do, to get that level of control, you have to get into the brain.”

Nicolelis says his goal is to use brain implants to allow the disabled to walk again. He has already started designing a wearable robotic “exoskeleton” that could help power paralyzed legs — think Wallace and Gromit’s “The Wrong Trousers,” only with better control. Nicolelis is also developing something called “shared control” in which a robotic limb is triggered by a basic command from the brain, but refines and carries out the movement itself, using preprogrammed intelligence. “The hurdles ahead, after finding even better electrodes, are developing prosthetics that are more amenable to brain control,” he says.

Many of the labs looking at brain implants started out doing basic research into understanding how small numbers of neurons worked. The research required the development of thin wire electrodes that could cozy up to individual neurons, a legacy that led to fully implantable devices. But for many applications, simpler signals, which can be picked up without undergoing major surgery, may suffice.

At the Wadsworth Center, the laboratory arm of the New York State Health Department, John Wolpaw and his team recently proved that a hat not unlike a swimming cap peppered with electrodes could pick up clear enough signals to allow the wearer to move a cursor around a computer screen. “There was an unsupported assumption that to get that kind of control, you needed to implant, but our work showed that’s not the case. These systems can do better than a lot of people give them credit for,” says Wolpaw.

Instead of tapping into the brain’s natural signals for moving limbs, Wolpaw’s system picks up changes in general brain activity that the patient must learn to control. “We look at rhythms on the EEG that are normally just idling, but we’ve shown that by using mental imagery, people can learn to make the signals stronger or weaker, and we can translate that into cursor movement,” says Wolpaw.

Wolpaw’s patients are trained over 10 sessions, during which about 80 percent learn to control their brainwaves well enough to move a cursor around a screen. In time, most can do other things, such as think of answers to questions to select on-screen, without it interrupting their control. The risks of the technique are undoubtedly fewer than for full brain implants, though questions remain about the effects of forcing the brain to change its activity, in a way the electrodes can pick up. “It’s probably just like learning anything else. There’s been no indication that any of this does anything harmful, and it’s hard to see how it could, but we can’t say for sure,” says Wolpaw.

While Wolpaw has achieved control many thought impossible without implanting electrodes directly into the brain, he feels a third technique, called electrocorticography, or Ecog, might have the brightest future. Ecog involves a smaller operation to place a small sheet of electrodes on the surface of the brain. “With this, you get strong signals, you can pick them up from smaller areas, but you’re not sticking something into the brain,” he says. Preliminary trials show patients can learn to use Ecog devices much faster than electrodes placed on their scalps.

More than likely is that all three techniques will co-develop, each finding its own niche. Full implants may only be worthwhile for the severely disabled, who need to control complex machinery, such as prosthetic limbs, with their thoughts. For many, though, regaining even the most minor level of independence would help. “One fellow said to me, ‘I just want to be able to scratch my nose,’” says Donoghue. “It’s easy to forget the kinds of extraordinary things people can’t accomplish. If you can do something that lets them reach out to the world even a little, it can make a huge difference.”

“The Joy of Laziness” was written by a German father and daughter team. Peter Axt, say the publishers, is a former health sciences expert at Fulda University near Frankfurt, and Michaela Axt-Gadermann is a practicing dermatologist. The book begins with an explanation that we are all born with a limited amount of “life energy.” If we use it all up quickly — by exercising and getting stressed out — we will die early. If we do very little and live life at a snail’s pace, we can eke it out and live much longer.

It’s a theory that doesn’t find much support in the scientific community. “The idea’s been around nearly 100 years and we know that it’s wrong,” says Tom Kirkwood, codirector of the Institute of Ageing and Health at Newcastle University.

The authors illustrate their ideas on life energy by looking at how much longer wild animals live if kept in captivity. “While wild animals cover many miles daily in search of food, and consequently are under a great deal of stress, zoo animals lead a very restful and relaxed life,” they write, before citing how lions in the Serengeti live only eight years, but can live to the age of 20 in a zoo. Arctic polar bears may last only 20 years in the wild, but 40 in captivity. “Laziness and downtime are important for your health. It is well known that lazy animals have the longest life expectancy,” says Axt-Gadermann, who adds that priests, nuns, monks and artists also have long lives.

But the idea of life energy is seriously flawed, says Brian Merry, an expert on aging at Liverpool University. Putting an animal in a zoo has no effect on how quick it ages, he says. “A blue tit in your garden has about a 50 percent chance of dying in its first year. Put it in an aviary and it might last up to 12 years. What you’re doing is exactly what we’ve done for ourselves. You’re taking it out of the natural environment where individuals die mainly through starvation, disease, predation, accidents and so on and you’re protecting them from all those things. You’re not doing anything to slow their aging.”

The book goes on to warn against the dangers of too much exercise. Physical exertion increases the production of free radicals — an extremely reactive form of oxygen — that damage our bodies and so speed up aging. But while free radicals are certainly suspected of playing a major role in the aging process, exercising is not believed to speed aging because of how the body responds when we are physically active. “It’s true that if you’re working yourself harder, you’re burning up oxygen, and it is through burning oxygen that you contribute some of the damage that makes us age, but what happens when you stress yourself with exercise is that you boost your body’s capacity to handle the damage that these free radicals cause,” says Kirkwood. “If anything, you end up being better off.”

He concedes that too much exercise can be a bad thing, but how much is too much? It depends on the individual. But push too much and you are likely to damage joints so much they can’t recover. Some scientists suggest that overexercising can also weaken the immune system. “Supreme athletes sometimes get very obscure viral infections that can end their careers,” says Merry.

Having warned of the dangers of doing too much exercise, the book outlines how staying calm is essential for a longer life. By avoiding stress — and what better way to do that than by sitting around and doing nothing — levels of stress hormones such as cortisol will be kept to a minimum, the authors say.

Cortisol certainly can have health effects, suppressing the immune system and possibly damaging certain types of cells in the brain, but most of these effects are believed to become a problem only when a person is stressed for a long time, rather than in brief bursts. “When the body is subjected to mild stresses, the cells turn up their natural defenses. If a body is left in a completely unstressed state, it doesn’t do as well as if you apply a little bit of stress,” says Kirkwood.

If avoiding stress is the authors’ shield against aging, laughing is their sword. And not without good reason. Laughing, they say, releases the feel-good chemical serotonin that makes us feel happy and relaxed. “There is evidence that laughing is good for you — certainly being able to laugh at life does help you to age better,” says Kirkwood.

Axt-Gadermann says there are three things we need to do to ensure a longer life. “First, stay cool and calm.” Avoiding stress wherever possible helps reduce our levels of stress hormones, which speed up aging. Second, get enough sleep. And third, eat less or fast for two days a month, as cutting down on calories “is the most effective way to prolong your life and avoid illness,” she says.

According to Kirkwood, the main problem with “The Joy of Laziness” may be the message people take from it. “The idea that we should learn to relax if we’re living a very pressured and stressed life is entirely right, but the reasons given in the book for arguing against the benefits of exercise simply don’t hold water.” If people exercise less, they are more likely to suffer from obesity and cardiovascular disease and suffer muscle wasting as they get older, all of which will severely impact on their independence and the quality of their lives. “Things need to be stimulated and used in order to keep them in tiptop form,” he adds.

“A book like this can be quite damaging. There’s a lot of evidence that exercise is beneficial for healthy aging and for many people it’s already a struggle to do any exercise. Anything that undermines the well-informed message about the benefits of exercise is potentially very damaging because it provides an excuse. It’s the copout that all too many people will jump at,” Kirkwood warns.

Undeterred, Cabanac lined his students up against a wall. It was going to be bad, but not as bad as they might have thought. He got them to sit as if perched on an imaginary stool, a position that forced their weight onto their knees. “Try it,” he said. “The pain soon becomes unsufferable.” Cabanac then promised the students increasingly large lumps of cash to endure the pain. The more he offered, the longer they suffered. The longest lasted for eight minutes 20 seconds.

Ironically, Cabanac’s experiment was part of a broader investigation into the science of pleasure. His aim was to find out what, if anything, was the point of pleasure. His conclusions, and those of other scientists working in the field, suggest that not only is pleasure good for our health, but it is at the root of our ability to make sense of the complex world in which we live.

Cabanac’s proof that people will suffer pain for payment will come as no surprise to the millions who do things they hate in return for a monthly paycheck. But in a follow-up experiment, Cabanac showed there was a more fundamental point to make about what influences our behavior.

Before the second test, Cabanac asked people to rate the pleasure they got from playing a video game. They were then placed in a temperature-controlled room and Cabanac, while cooling it down, asked them to rate how unpleasant the feeling was. He then combined the two experiments. “We cooled the room down, and every time, the same thing happened. As soon as it was cold enough for their displeasure rating to just outweigh the pleasure of playing the game, they stopped the experiment,” he says.

According to Cabanac, the tests show that while it might not be obvious all the time, each of our decisions is ultimately driven by pleasure seeking. “Pleasure is the common currency that allows us to make any, and I mean any, decision in our lives,” he says. “Any decision is made according to the trend to maximize pleasure.”

Pleasure seeking certainly makes evolutionary sense. As organisms developed, the emergence of pleasure as a sensation would have helped reinforce healthy behavior, such as eating certain foods, having sex and keeping warm. But while Cabanac’s theory might make evolutionary sense, that doesn’t make it correct. It doesn’t take long to think of examples where a decision looks entirely unpleasurable. What about a decision that ultimately leads to a person’s own death? How could that choice come out as the most pleasurable path to take?

In 1969, Jan Palach, a Czech student, set himself on fire in protest at the Soviet invasion of his country. He died from his injuries three days later. “That’s an atrocious death, yet he did it by choice,” says Cabanac, who assumes Palach was not mentally ill. “The fact that he was suffering hell by dying by fire was compensated for by an overwhelming joy of telling the Russians, ‘Look. Look what we are able to do against you. You do not win.’”

At the Neurosciences Research Institute at the State University of New York, director George Stefano believes that pleasure is not only the driver for every decision we make but a crucial component for making sense of the world. “As human beings, we always pride ourselves in being rational, but if we were 100 percent rational, we would have to weigh every single possible action we might take at any time. Imagine how time-consuming that would be. Even a cognitive organism doesn’t have time to be truly rational,” he says. Pleasure, says Stefano, is our brain’s way of shortcutting the rational process by subconsciously and continuously ranking what is most important to us from the vast number of options we are faced with. Stefano’s phrase for it is likely to make dedicated hedonists smile: “Pleasure leads to pure rationality,” he says.

As with the majority of neuroscience, some of the most reliable evidence comes from studying people who were born with, or have later suffered, damage to specific parts of the brain. At the University of Iowa, a team lead by neuroscientist Hanna Damasio has been studying people with lesions in a region of the cortex associated with pleasure. They found that although the patients had no intellectual impairment, in a simple gambling test they made hopeless decisions. “They are oblivious to the consequences of their actions,” the team noted in a paper published in the journal Brain.

Despite decades of effort, scientists are still teasing out the precise neural circuitry that allows us to experience pleasure. In the 1980s, many scientists believed there was just one major brain circuit that governed pleasure. Triggered by the neurochemical dopamine, it excited the cerebral cortex and other areas of the brain such as the amygdala and nucleus accumbens. But more recent research has cast doubt on the role of dopamine. It now seems the chemical plays a subtly different role — making us feel desire rather than pleasure.

Scientists now know that another brain circuit, triggered by chemicals called opiods, plays a key role in pleasure sensations. Injecting drops of opiod into a part of the brain called the ventral pallidum heightens the enjoyment of sweet tastes, they found, suggesting it boosts the natural pleasure sensation. Meanwhile, at Oxford University, a team led by neuroscientist Edmund Rolls has discovered that a region of the brain called the orbitofrontal cortex (OFC), which lies just behind the eyes, contains bundles of cells that are triggered by different types of pleasurable experience. Signals from the OFC are then thought to feed into the dopamine and opiod circuitry.

According to Cabanac, pleasure can only be a transient sensation, the feeling of warming up when cold, or of eating when hungry. He believes that the lack of these gaps between how we feel and how we want to feel explains a lot of misery in modern society. “We’re not hungry, we’re not cold, we have everything,” he says. The result, he says, is that we are tempted to seek pleasure in other ways, by taking drugs or overindulging in pleasurable activities. Extremely hedonistic lifestyles may be caused by compulsive behavior leading to an endless craving for pleasurable sensations, or subtle damage to the underlying brain circuitry, he adds.

Of course, it’s possible to have too much of a good thing, and pleasure can easily become pain. This flipping of pleasure into pain has been investigated using brain scans focusing on the OFC, which have captured the fine line that is the difference between the two states. Marilyn Jones-Gotman of the Montreal Neurological Institute at McGill University recruited self-confessed chocoholics and fed them lumps of chocolate while monitoring their brain activity using a brain-scanning technique called positron emission tomography. After each chunk, the person was asked to rate how much they wanted another piece. “We fed them until they absolutely could not face another bite,” she says.

Jones-Gotman found that as the experience of eating chocolate flipped from being intensely pleasurable to downright repulsive, activity in the orbitofrontal cortex shifted from the center to nearer the outside. They had captured the exact point where pleasure became pain. But is this the change that tells us when we’ve had too much of a good thing? Jones-Gotman doesn’t think so. “If you’re overeating, especially in cases like Christmas dinner when you’re eating food that people like very much and associate with the good feeling of previous Christmases, you probably won’t stop until it’s actually painful,” she says.

While pleasure may have evolved as a way to encourage creatures to indulge in healthy behavior and avoid more harmful pursuits, Stefano believes there is another benefit. Inside brain neurons, and also other tissues in the body, is a chemical called proenkephalin. He says that when we experience pleasure, proenkephalin is broken down, producing a substance that causes a feel-good sensation. But the same enzymes involved in that process also release another chemical called enketylin, a strong antibacterial agent. “Just think of the beauty of that: When you’re feeling good, you protect yourself,” says Stefano.

Though scientists are slowly teasing out the secrets of pleasure, they have a long way to go. One problem is that little funding goes into looking at why things go right in humans. Instead, money is poured into researching disease and disorders. “It’s time that changed a little,” says Stefano. “Feeling good is healthy. Why don’t we look into it?”

Earlier this week, scientists reported that we may have less time to combat global warming than we realized. Measurements of carbon dioxide, a greenhouse gas, taken from the Mauna Loa Observatory, 12,000 feet up a mountain in Hawaii, suggest atmospheric carbon dioxide levels have risen sharply and inexplicably in the past two years, prompting fears of runaway global warming. Though it is too early to confirm that it is a definite upward trend, the results came as an unwelcome surprise to climatologists.

Over the span of the coming century, even the most extreme global warming scenario predicted by the Intergovernmental Panel on Climate Change — an increase of 5.8 degrees Celsius — seems gentle. Surely civilization will have enough time to protect itself against the consequences, while ecosystems could gradually adapt? Not so, say scientists studying the world’s weakest links.

John Schellnhuber, research director at the Tyndall Center for Climate Change Research in Norwich, U.K., played a key role in identifying the dozen systems where global warming could produce sudden and dramatic environmental damage. He calls them the “tipping points,” the Achilles’ heels of the planet. At a conference earlier this year, Schellnhuber and other scientists called for a concerted, global effort to investigate the Earth’s known tipping points and to search for new ones. Only then, he says, will we be able to identify where the consequences will be felt first.

“It’ll take a global effort to understand these, and we have to make sure that none are activated through human actions,” he says. Here, we present a list of the tipping points and what might happen if they are triggered.

Sahara desert
Occupying some 3.5 million square miles of northern Africa, the Sahara Desert is expected to shrink with global warming as more plentiful rain brings a flourish of vegetation to its southernmost reaches. For those on the edge of the desert, the fertile land will undoubtedly be a boon, but the Sahara plays a broader role in the health of the planet. The dry dust that is whipped up from the desert by strong prevailing winds contains crucial nutrients that seed the Atlantic and may even help fertilize the Amazon.

As the Sahara turns from brown to green, the flux of nutrients into the ocean is expected to drop, restricting food available for plankton, the smallest of links in the marine food chain. As the number of plankton falls, so does food for aquatic creatures further up the food chain.

That’s not the only knock-on effect. Plankton lock up the greenhouse gas carbon dioxide from the atmosphere, and so help counter global warming. With fewer plankton, the oceans will take less of the gas from the Earth’s atmosphere.

Dust from the Sahara has other, more subtle influences. When blown out over the Atlantic, clouds of Saharan dust act to stabilize the atmosphere, suppressing the formation of hurricanes. A greener Sahara could mean more frequent, or more severe, hurricanes slamming into the Caribbean, parts of Central and South America and the Southeastern U.S. Meanwhile, the now wetter Saharan regions of Sudan, Morocco and Algeria could become more prone to infestations of locusts, such as the swarms that have devastated crops in the region this year.

Amazon forest
The size of western Europe, the Amazon forest is one of the most biodiverse regions on Earth. Models suggest that with global warming will come a drop in Amazonian rainfall, leading to the gradual death of the forest and subsequent collapse of the myriad ecosystems it supports.

The extinction of species is only one consequence of a warmer planet. As the trees die off, they will fall and rot, releasing carbon dioxide. In the worst-case scenario, the quantities of carbon dioxide emitted could be of the same order of magnitude as from the 20th century’s total fossil fuel output.

“It’s the biggest biodiversity pool on Earth, and if it were lost, it would be an incredible loss for our nature capital. This is not just a fantasy. There’s clearly a vulnerability here,” says Schellnhuber.

Greenland ice sheet
The Greenland ice sheet holds about 2.6 cubic kilometers of fresh water, which is some 6 percent of the planet’s supply. It is imperative that this water remain frozen. If global warming sees temperatures rise by more than about 3 degrees Celsius, Greenland is likely to begin a slow thaw, steadily releasing all that water — currently resting on land — into the north Atlantic Ocean.

Climate models suggest that a more drastic temperature increase of some 8 degrees Celsius could see the Greenland ice sheet disappear almost entirely, a thaw that would see the seven seas rise by seven meters. Such a dramatic rise in sea level would cause flooding that is bound to have a devastating impact on people living on unprotected shorelines around the globe.

And the drowned land wouldn’t reappear for some time. “If the Greenland ice sheet goes, it probably will not come back for the next 60,000 years,” says Schellnhuber.

North Atlantic current
The North Atlantic current is one of the strongest ocean currents in the world, of which the Gulf Stream is the precursor. It works like a conveyer belt. Surface water in the North Atlantic is first cooled by westerly winds from North America, making the water more dense and salty so it sinks to the ocean floor before moving toward the equator. Driven by winds and replacing the cold water moving south, warm water from the Gulf of Mexico moves upward into the Atlantic. The effect of the current on climate is dramatic. It brings to Europe the equivalent of 100,000 large power stations’ worth of free heating, propping up temperatures by in excess of 10 degrees Celsius in some parts.

Global warming could change all that, though not very quickly. Computer models predict that as global warming increases, so will rainfall in the North Atlantic. Gradually, the heavier rains will dilute the sea water and make it less likely to sink, a process that could bring the whole conveyer to a gradual halt. “It won’t happen in a matter of weeks, like in the movie ‘The Day After Tomorrow,’ but it could happen over a few decades,” says Schellnhuber.

In the past 50,000 years, the current has stopped at least seven times. Collapse of the North Atlantic current would hit Iceland, Scotland and Norway most, where temperatures could drop 10 degrees Celsius or more. If it happened soon, we would notice a difference. But in 100 years, when global temperatures may be a few degrees higher anyway, temperatures may simply revert back to today’s levels. Total shutdown of the current would lead to a rapid regional sea level rise of around one meter along the U.K. coast as the ocean adjusts to the change.

Methane clathrates
Deep within the Siberian permafrost and ocean floor sediments lie vast deposits of gas-filled ice called methane clathrates. At Siberian temperatures, or under the weight of icy oceans, the clathrates are stable. But as global warming takes effect, the icy crystals that clutch the gas could rupture, releasing it into the oceans and atmosphere. According to the U.S. Geological Survey, some 10 to 11 trillion tons of carbon are locked up in clathrates in ocean floor deposits, the equivalent of 20 times the known reserves of natural gas. Some scientists believe sudden releases of methane from clathrates caused a severe environmental impact in the past.

If released into the atmosphere, methane from clathrates could exacerbate global warming. Some estimates suggest that since methane is such a strong greenhouse gas, a significant release could increase global warming by up to 25 percent. More likely, some scientists say, is that released methane would poison the oceans or oxidize and dissolve as carbon dioxide as it rises, which would still be toxic to some species.

The monsoon
During March and April, the Indian subcontinent begins to heat up, reaching some of the highest surface temperatures of the year by May. The hot land produces a sharp temperature gradient between the land and sea, which causes an abrupt reversal of the winds from seaward to landward.

As the winds strike the Himalayas and are deflected upward, they create a low pressure system, forcing rain clouds to release their stores of water. While the monsoon season can cause incredible flood damage, local populations are largely adapted and to some extent reliant on the weather.

If global warming has the expected effect of heating India even more, the monsoon season could become far more severe. What happens will be influenced by the level of pollution in the region. Sulfur dioxide and even dust make rain droplets smaller and so diminish overall rainfall. These substances also increase the reflectivity of clouds, which prevents the ground from heating up so much. Both of these factors would weaken the monsoon, causing havoc for Indian agriculture, with serious consequences for food production.

Ozone hole
Decades after many countries introduced a ban on CFCs, the danger of the ozone hole causing a nasty surprise remains very real. “In a sense, this is the mother of all tipping points, and it’s one that has been activated already,” says Schellnhuber.

Scientists are now generally agreed that global warming may drastically amplify the power of ozone-destroying chemicals, which linger in the stratosphere for decades. At high altitude, ozone acts as a shield against the sun’s damaging radiation. Global warming, while heating the lower atmosphere, can lead to cooling in the stratosphere where the ozone layer forms. Cooling this band of air has a complex knock-on effect, disrupting a chemical process that prevents ozone from breaking down. The result is a loss of ozone as the world warms up.

Though the ozone hole is often associated with Antarctica and Australia, ozone loss due to global warming could see a hole appear over parts of Europe. “If it were to stretch beyond Antarctica, it would increase, in an intolerable way, the risk of skin cancer and blindness,” says Schellnhuber.

Tibetan plateau
Spanning one-quarter of China’s entire landmass lies the Tibetan plateau. Because the region is permanently under snow and ice, it behaves like a giant mirror, reflecting the sun’s rays back into space. The effect is to keep a lid on global warming, at least locally, as the darker soils are unable to bask in the sun’s radiation and increase in temperature.

In a warmer world, the white of the Tibetan plateau will slowly turn to brown and gray as the snow retreats to reveal the ground beneath. As the ground warms, melting will accelerate. Tibet will become a much warmer place.

Salinity valves
In some parts of the world, local geography conspires to pinch the waters between adjacent seas into separate bodies of water. If one is saltier than the other, a flux of salt, nutrients and oxygen can be set up across the gap, producing what scientists refer to as a salinity valve. Arguably the most significant salinity valve is the Strait of Gibraltar, acting as a pinch between the Mediterranean and the north Atlantic Ocean. The gradients across the valves give rise to unique ecosystems that are highly adapted to local conditions.

As global warming is expected to disrupt ocean currents, by warming the seas and diluting the surface waters that drive other water circulations, marine life around salinity valves could in turn face major disruption. “Everything is in a balance now; all the ecosystems have adapted to a certain salinity,” says Schellnhuber. If conditions around salinity valves change rapidly, those ecosystems might not be able to adapt quickly enough to survive. “The Mediterranean is very fragile already. It could have an extremely negative effect for several decades,” adds Schellnhuber.

El Niño
The disruption caused by El Niño is well known, from droughts in Asia and Australia to flooding in regions such as Ecuador and northern Peru. The Peruvians gave El Niño its name, derived from the Spanish for “the boy child.” El Niqo was originally used to describe a warm ocean current that arrived around Christmas time.

Nowadays, the term refers to a general warming of the central and Asian Pacific, which causes a major shift in weather pattern and in particular responds sensitively to changes at the western boundary of the Pacific. El Niños are already somewhat erratic, occurring every two to seven years, but some models suggest global warming could make El Niño not just more severe but more frequent.

The impact on agriculture and so food production could be serious. Indonesia, the Philippines, Southeast Asia and eastern Australia could face damaging droughts while the heavy rains and flooding cause problems for the northwestern regions of South America.

West Antarctic ice sheet
The giant West Antarctic ice sheet is not about to melt anytime soon — the ice is up to a kilometer thick — but two years ago a vast chunk, the Larsen B ice shelf, broke off the eastern side of the Antarctic peninsula and fragmented into icebergs. In just 35 days, about 3,250 square kilometers of ice was lost; the size of the entire shelf is now roughly 40 percent of the size at which it had previously stabilized.

Some predictions suggest that the rest of the sheet could feel the force of global warming quickly. Should the entire sheet melt, it is estimated the sea level rise around the world would top six meters. Once more, coastal regions would be under threat.

The Atlantic circumpolar current
Some scientists believe the Atlantic circumpolar current to be the most significant on the planet. It swirls some 140 million cubic meters of water around Antarctica every second, mixing water from the Pacific, Atlantic and Indian oceans as it goes. The current taps into another circulation that sees cold surface water sink while warmer water rises, bringing with it vital nutrients from dead plankton and other marine life on the ocean floor.

Global warming is expected to produce more rainfall over the poles, which could slow the rise of nutrients for dispersal by the Atlantic circumpolar current. “For marine life, any change in the currents is extremely important,” says Schellnhuber.