Top 10 STRANGE and Fascinating Facts About ICE

Top 10 Strange and Fascinating Facts About Ice We usually don’t think about ice too much, unless there’s none in the freezer and all we have to drink is a warm can of Coke. Artificial refrigeration has been around for almost a century now, and it’s safe to say that we take ice for granted, just as we will take food for granted when the replicators come online. But the cold, hard, slippery truth is that ice deserves more consideration than that- and not just the kind you put in your drink. There’s much to be learned about our past, present and future from studying the cold stuff, so grab yourself a nice beverage or a refreshing popsicle and prepare for a brain freeze. 10. Ice Harvesting Before the advent of freon-based refrigeration in the early 1900s, ice was the only way to keep things cool (and food from spoiling). While there were ice-making machines in use in the mid- to late-1800’s, they were mostly for commercial use – beef packing plants and the like – and also used d1angerous chemicals such as ammonia and ether.

But ice was still needed for the home, and commercial ice harvesting was a huge business around the turn of the century. The process was every bit as labor-intensive as one would imagine it to be without the use of modern tools- gigantic ice picks and saws, along with horses pulling around what amounted to huge ice plows, were common for larger jobs, which could employ dozens of men for months at a time. Ice was then conveyed mechanically or by river to an ice house. Thousands of small, private ice houses- along with dozens of much larger, commercial ones- dotted the American landscape at this time. Ice houses were double-walled, tightly insulated structures packed with sawdust and other insulating materials, capable of keeping large amounts of ice through the warm months. One of the larger ice houses, on the shore of Connecticut’s Bantam Lake, was the length of two football fields, contained fourteen compartments, and could store 112 million pounds of ice.1 Much of this ice departed daily by train, for the larger cities including New York- up to twenty cars full per day. Of course, it still had to make its way to the home, which is why before refrigerators, there were… 9.

Ice Delivery and Iceboxes As one might imagine, New England dominated the early ice industry. It had plenty of the stuff to harvest each year, and sawdust from its many timber mills was readily available for insulation. Frederick Tudor, father of the New England ice trade, was shipping ice all over the world by the middle of the 19th century; cleverly, he mitigated the shipping costs by shipping fruit and other perishables along with the valuable ice. By the turn of the century, the icebox was just as common in American homes, grocers and restaurants as electric refrigerators are today. As you can see from the illustration, the principle was largely the same: ice was kept in a top compartment; as the air cooled, it was forced down to where the food was stored; warmer air rose, where it would be cooled by the ice, and so on. Melt was caught in a drip pan underneath the unit, and every morning, the friendly neighborhood Ice Man would come by with another fresh chunk for you. Depending on the region, ice could be gotten for as little as four cents per pound. Old-fashioned ice boxes were often beautifully hand-made; since they were not necessarily thought of yet as kitchen appliances, their look was more in line with living room decor.

8. Density If you punch the surface of a lake, and then a block of ice, you’re probably insane. You also might be tempted to think that ice is far denser than water. While there is no disputing that ice is HARDER than water, this would display a misunderstanding of the scientific property of density. One curious property of ice is that as it freezes, it expands (this is why standing water in your pipes will cause them to burst if they freeze). Put another way, as water freezes, it retains the same mass while taking up more space- about 9% more. This means that ice is actually quite a bit less dense- its molecules are spaced farther apart- than water, which reaches its maximum density at about 40 degrees Fahrenheit (slightly above freezing). This is why ice floats in water– which, actually, is a pretty important mechanism for life on Earth. It’s also what causes potholes in the road in cold areas, and why a can of soda will burst when frozen.

7. Different Types While most probably figure there is more than one type of ice, there are actually sixteen that are known to science. Their different properties present themselves at different atmospheric pressures and temperatures; Ice IV is the kind you find in the freezer. Among the types that science has helpfully labeled I through XV (9), the major differences lie in the structures of the crystals; some strange properties emerge under certain conditions. For example, Ice XI is ferroelectric- it exhibits electric polarization, which can be manipulated and reversed. Ice V has the most complicated crystalline structure; Ice III is actually denser than water, and would sink if you put some in your glass. Strangest of all is the one type not classified by number, which is called amorphous ice. It has no crystalline structure, and is the type of ice most often found in space; there are also three different types (depending on density) of this amorphous ice, which is closest to simply being a solid form of water- it’s actually classified as a mineral.

6. Slippery When Cold So, why is ice slippery? Sure, it’s made out of water, but what about ice that’s at far below freezing temperature? It stands to reason that if it’s ten below freezing outside, the ice should be frozen hard enough to be a solid surface, with no liquid water on it, and that it should not be slippery enough for us to fall and damn near break our tailbone on the way to work. This, obviously, is not the case. Before the phenomenon was properly understood, science took an educated guess that sounded right, so it was widely taught in textbooks; basically, that friction (caused by your foot) caused an ever-so-slight raising in temperature at the surface of the ice, which produced a microfilm of water, which made you slip before immediately freezing up again. It sounds plausible, but unfortunately, it was a bit off the mark. The real reason has to do, again, with ice being less dense than liquid water. Scientists within the last decade have come to believe (no, this is still not completely understood) that because of this difference in density, and through a principle that would take six (very boring) lists to explain, surface molecules of ice- those in contact with air- cannot bond properly to the mass of molecules beneath.

These surface molecules essentially retain liquid properties while being solid ice, and even we couldn’t make up an explanation that cool for ice being slippery. 5. Commercial Production When one thinks about a world without refrigerators, it’s easy to imagine how gigantic an industry commercial ice production must have been a hundred years ago. What’s really mind-boggling is just how enormous an industry it remains to this day- only now, of course, it’s produced mechanically instead of harvested from natural sources. Commercial ice makers today produce three main types- flake (shaved ice), tubular (the little pellets you still see in some ice machines), and plate (regular cubes). In addition to being bagged and sold commercially, it has many industrial uses including the manufacturing of chemicals, and is used in mixing concrete. Believe it or not, there’s enough demand for ready-made ice that, as recently as 2002, a census study showed over 400 ice production companies generating almost $600 million annually in the United States.

That’s JUST from producing and selling ice, and doesn’t even count companies that manufacture smaller ice makers for food service and such. 4. Building Material When we think of structures made of ice, it’s safe to say that not a lot jumps to mind beyond the igloo. But ice has shown to have many practical uses in building- and some NOT so practical, if totally dazzling. For example, Antarctica’s McMurdo Sound is a remarkably inhospitable place. Fuel tankers and supply vessels had a hell of a time even docking there until 1973, when the U.S. Navy devised an ingenious solution to the difficulty of building a pier in the ice- they built a pier FROM the ice. The process has since been perfected, and five more such piers built, each lasting several seasons before being allowed to melt. Attempts have even been made- not quite so successful- to build structures or vessels out of what is called pykrete, which is a mixture of 86 percent ice with 14 percent wood pulp. The pulp reinforces the naturally brittle ice, resulting in an extremely resilient- if obviously temporary- substance.

The British military considered the viability of building warships out of the substance during World War II (it was not viable). And finally, there is the more recent phenomenon of ice hotels like the one shown above, which pop up annually during the cold season at various locales inside the Arctic Circle. Such hotels typically use ice not only for the architecture but the furniture, light fixtures, even drinking glasses and art objects. Polar-rated sleeping bags are the only real amenity, which is great, since they’ll be necessary for surviving your stay. 3. Glaciers Glaciers don’t exactly ignite the public imagination, even if one played a co-starring role in a very successful movie about a famous, doomed ocean liner. But consider the facts that water is obviously important to human life, that glaciers are made of water, and that ten percent of the Earth is covered with them.

In fact, fully three quarters of the fresh water in the entire world is contained in glaciers. Think about that; the volume of every fresh water lake in the world is nothing compared to the volume that sits frozen around the Earth’s poles, and if all of the glaciers in the world suddenly melted, we’d all be a couple of hundred feet underwater as a result. Also, seasonal glacial runoff is an incredibly important source of fresh water- for example, in Washington state alone, 470 billion gallons of water are produced each year from glacial melt. One glacier range in the Canadian Arctic has been found to produce ten percent of the glacial melt in the entire world. The range is the size of the state of New York, and is pretty much a primary reason for rising sea levels worldwide. 2. Ice Core Drilling The Greenland Ice Sheet covers 80% of that land mass- the world’s second-largest body of pure ice, after the one in Antarctica. At the bottom of it, miles below the surface, there is ice that froze over a hundred thousand years ago. In 1955, scientists began drilling there, collecting core samples of the ice; over the decades, many tools and techniques have been developed for extracting very well-preserved ice samples from far, far below the surface.

Contained therein is a record of climate change all throughout history. Using air samples trapped inside the ice, scientists are able to gather information about the temperatures and greenhouse gas levels of hundreds of centuries past. They hoped to determine how hot surface temperatures were during the last interglacial warm period before our current one, and how the planet coped- and thereby, perhaps gain insight as to how we could do the same if temperatures continue to rise. And they may have been successful. The most recent research suggests that temperatures were up to eight degrees hotter during this period- the Eemian period- than the present day, and sea levels 13 to 26 feet higher … in other words, “a number of environmental climatic conditions that could possibly be reproduced in the future.” 1. Indicator of Extra-Terrestrial Life Finally, as alluded to earlier, ice is everywhere in space.

Hydrogen and oxygen are among the most plentiful elements in the Universe – in fact, scientists believe that most, if not all, of the water on Earth came from ice-bearing comets and asteroids that smashed into the planet in its infancy. Being a requirement for life as we know it, liquid water would be great for astronomers to find on some distant planet- but ice would be almost as good. Life has been found on our own planet, in the form of microscopic organisms and tiny shrimp, beneath the previously mentioned ice shelves of the Antarctic, an environment long thought uninhabitable by life of any kind; why not on the brutally cold surface of another planet? Or, perhaps even a moon- Jupiter and Saturn both have moons chock full of ice, with other conditions science thinks may have at least once been favorable to life. All food for thought the next time you’re pouring your sun tea over ice, the stuff that may hold the key to the search for intelligent life in the Universe..

Ice Ages & Climate Cycles

As we try to unravel Earths history we look for signs in the landscape that provide indications of former episodes of extreme climates. In North America we recognize evidence of a recent ice age and wonder if it has ended or if we are just in a brief warm interlude before another cold interval. We have two learning objectives for this lesson. First to discuss the characteristics of ice ages and second to consider how the changing extent of glaciers and ice sheets is influenced by other components of the Earth system. We can identify several ice ages during the last billion years of Earths history. During these times thick glaciers and ice sheets covered large regions of Earth. Extensive glacial deposits provide evidence of massive ice sheets that may have extended almost to the equator near the end of the Proterozoic era creating a condition known as Snowball Earth.

Ice ages in the first half of the Phanerozoic era indicate times of cooler temperatures and lower greenhouse gas concentrations The most recent ice age, the Pliocene-Quaternary, began less than 3 million years ago and many scientist interpret data from this event to suggest that we are technically still in this ice age. During its maximum extent, a sheet of ice a couple of miles thick would have advanced southward out of Canada before retreating again as climate warmed. So why do we get ice ages? Ice ages last for millions of years and are generally related to the relative position of continents and oceans. As you might expect locating continents over a Pole allows ice to build up and may result in an ice age. This was the case for the events of the Karoo ice age when several pulses of glaciation occurred over a span of about 100 million years in the Paleozoic Era.

However, 3 million years ago the distribution of continents was not much different than today. With one significant exception, water was flowing freely between the Atlantic and Pacific Oceans through a narrow gap that separated North and South America. That gap soon closed and circulation patterns in the Atlantic Ocean changed leading to more humid air carried further north and resulting in an increase in precipitation and the development of ice sheets in northern latitudes. Contrary to what many people think, ice ages are not continuous times of extremely low temperature. For example, examine this graph to see how temperature varied over 450,000 years This includes the most recent part of the Pliocene Quaternary ice age As you can see an ice age is actually characterized by a series of shorter climate cycles composed of alternating pulses of warmer and colder temperatures. We can observe a series of longer cold intervals known as glacials that are interrupted by shorter warm intervals known as interglacials.

These alternating cold and warm intervals reflect the advance and retreat of glaciers. The interglacials last for 10,000 to 20,000 years. We may actually be in an interglacial now. Or maybe the ice age has ended. We'll just have to wait about 10,000 years to find out. If you look more closely at the graph you can see that even within cold glacials there are significant fluctuations of temperature resulting in colder or warmer intervals. All of these changes can be explained by small changes in the shape of the Earth orbit and/or the inclination of Earth's axis. Temperatures in the polar regions become colder if Earth's orbit takes it farther from the sun during winter. and if there is an increase in the tilt of Earths axis. Over the course of tens of thousands of years these types of changes have the potential to drastically change Earth's climate. When they all align in just the right way they can lead to substantial warming or cooling trends to generate glacials and interglacial cycles as well as shorter more frequent cycles within these intervals.

Okay, so now we know that several long lasting ice ages have been triggered in Earth's history due to changes in the relative positions of continents and oceans and that climate cycles through warm and cold intervals during these events. but what causes an ice age to be sustained or to end. We'll consider the factors to help sustain an ice age to be positive feedbacks and processes that lead to the end of an ice age as negative feedbacks. Perhaps the most significant positive feedback arises from the ice itself. Ice and snow make very reflective surfaces, the term albedo is used to describe the reflectivity of a surface. Bright, shiny or light colored surfaces have high albedo values and will reflect solar radiation. Reflection results in less solar energy being absorbed at the Earths surface and produces a cooling effect.

In contrast, dark surfaces like forests or oceans have low albedos and will absorb solar radiation and become warmer. Positive feedbacks in the climate system would result in larger ice sheets. Ice sheets reflect solar energy causing less to be absorbed and leading to a decrease in temperatures, and thus sustaining the growth of the ice sheets and prolonging the ice age. Further, the growth of ice sheets would diminish the area of the globe covered in by dark ocean waters and forests. Further reducing the solar energy capable of being absorbed. In contrast negative feedbacks represent processes that result in an increase in temperature that would encourage melting of the ice sheets and the expansion of the oceans and forests. This might result from gradual changes in the distribution of continents and oceans or from an increase in atmospheric carbon dioxide concentrations.

Carbon dioxide and other greenhouse gases would trap heat close to Earth's surface, accelerating the collapse of ice sheets. Such an influx of gases would result from volcanic eruptions or from the decrease in photosynthetic activity due to cooler temperatures. So for today we had two learning objectives How confident are you that you could successfully complete both these tasks?.

Glaciers and Global Warming | MconneX | MichEpedia

My research involves looking at how ice sheets and glaciers break One of the things that we observed right around 2002, which was shocking, was the Larsen Ice Shelf, the entire peninsula, it’s a tiny little ice shelf But as far is anybody knows, it sat there there happily for ten thousand years, possibly a lot longer Then, over about six weeks, culminating in March 2002, The entire ice shelf completely disintegrated So it’s just gone And so we have these extremely rapid events that have potential to change the picture that… what we’ve always thought about ice sheets is that they change really rapidly When you think about things over a century we normally ignore the ice sheets like we used to because it’s gonna change really slowly That’s the way we’re used to thinking about it But this type of event completely upended our thinking about that that you could have really rapid changes that occur over days, weeks, maybe even less than a day So these are pretty dramatic changes We have an idea; we have a theory about how it’s happened, but we can’t predict it yet What are the likelihood that it happens to different ice shelves? What if it happens to one of the really big ice shelves? Then what’s gonna happen? We know that ice sheets are these huge masses of ice, and they’ve been there for a long time.

And we have smaller glaciers that have also been there for a while but not quite as long And the way they lose mass is they can either melt, or bits of ice can break off and if it’s in contact with the ocean, they float away and then they eventually melt And it turns out, for the major ice sheets Greenland and Antarctica, a significant portion of their mass is lost by breaking, by iceberg calving-is what we call it it’s about fifty percent maybe as high as seventy percent But it’s very uncertain; it’s a huge amount of mass and it’s really significant because we’ll occasionally get these icebergs that are the size of Massachusetts close to the size of texas sometimes the break off oversight then they float off paidcontent rupturing lanes eventually built into the ocean and is an important process that we need to understand the biggest question that we’re looking back is really how much age she scan contrary to seal to arise over the next century cell you’ve lived close to the ocean you probably want to know if segal was gonna rise by a meter or two which is the upper end of the estimates or maybe only five or ten or twenty centimeters which seems unlikely given what we’ve observed but we can entirely rule out this is one piece twelve the facts of global warming and one piece of intact open we don’t really understand how increased surface temperatures capture temperatures or function temperature taken effect if you move it up but there or hot water close to the asians we know what’s going on and leaving so is the big part of that and what do you start melton there’s going to get your adding fresh walking for changing the system and with the positive and negative feedback is interesting but we don’t know willful.


Earth in 1000 Years

Ice in its varied forms covers as much as 16% of Earth’s surface, including 33% of land areas at the height of the northern winter. Glaciers, sea ice, permafrost, ice sheets and snow play an important role in Earth’s climate. They reflect energy back to space, shape ocean currents, and spawn weather patterns. But there are signs that Earth’s great stores of ice are beginning to melt. To find out where Earth might be headed, scientists are drilling down into the ice, and scouring ancient sea beds, for evidence of past climate change. What are they learning about the fate of our planet, a thousand years into the future and even beyond? 30,000 years ago, Earth began a relentless descent into winter, Glaciers pushed into what were temperate zones. Ice spread beyond polar seas. New layers of ice accumulated on the vast frozen plateau of Greenland.

At three kilometers thick, Greenland’s ice sheet is a monumental formation built over successive ice ages and millions of years. It’s so heavy that it has pushed much of the island down below sea level. And yet, today, scientists have begun to wonder how resilient this ice sheet really is. Average global temperatures have risen about one degree Celsius since the industrial revolution. They could go up another degree by the end of this century. If Greenland’s ice sheet were to melt, sea levels would rise by over seven meters. That would destroy or threaten the homes and livelihoods of up to a quarter of the world’s population. These elevation maps show some of the areas at risk. Black and red are less than 10 meters above current sea level. The Southeastern United States, including Florida, And Louisiana.

Bangladesh. The Persian Gulf. Parts of Southeast Asia and China. That’s just the beginning. With so much at stake, scientists are monitoring Earth’s frozen zones, with satellites, radar flights, and expeditions to drill deep into ice sheets. And they are reconstructing past climates, looking for clues to where Earth might now be headed, not just centuries, but thousands of years in the future. Periods of melting and freezing, it turns out, are central events in our planet’s history. That’s been born out by evidence ranging from geological traces of past sea levels, the distribution of fossils, chemical traces that correspond to ocean temperatures, and more. Going back over two billion years, earth has experienced five major glacial or ice ages. The first, called the Huronian, has been linked to the rise of photosynthesis in primitive organisms. They began to take in carbon dioxide, an important greenhouse gas. That decreased the amount of solar energy trapped by the atmosphere, sending Earth into a deep freeze.

The second major ice age began 580 million years ago. It was so severe, it’s often referred to as “snowball earth.” The Andean-Saharan and the Karoo ice ages began 460 and 360 million years ago. Finally, there’s the Quaternary, from 2.6 million years ago to the present. Periods of cooling and warming have been spurred by a range of interlocking factors: volcanic events, the evolution of plants and animals, patterns of ocean circulation, the movement of continents. The world as we know it was beginning to take shape in the period from 90 to 50 million years ago. The continents were moving toward their present positions. The Americas separated from Europe and Africa. India headed toward a merger with Asia. The world was getting warmer.

Temperatures spiked roughly 55 million years ago, going up about 5 degrees Celsius in just a few thousand years. CO2 levels rose to about 1000 parts per million, compared to 280 in pre-industrial times, and 390 today. But the stage was set for a major cool down. The configuration of landmasses had cut the Arctic off from the wider oceans. That allowed a layer of fresh water to settle over it, and a sea plant called Azolla to spread widely. In a year, it can soak up as much as 6 tons of CO2 per acre. Plowing into Asia, the Indian subcontinent caused the mighty Himalayan Mountains to rise up. In a process called weathering, rainfall interacting with exposed rock began to draw more CO2 from the atmosphere, washing it into the sea. Temperatures steadily dropped.

By around 33 million years ago, South America had separated from Antarctica. Currents swirling around the continent isolated it from warm waters to the north. An ice sheet formed. In time, with temperatures and CO2 levels continuing to fall, the door was open for a more subtle climate driver. It was first described by the 19th century Serbian scientist, Milutin Milankovic. He saw that periodic variations in Earth’s rotational motion altered the amount of solar radiation striking the poles. In combination, every 100,000 years or so, these variations have sent earth into a period of cool temperatures and spreading ice. Each glacial period was followed by an interglacial period in which temperatures rose and the ice retreated. The Milankovic cycles are not strong enough by themselves to cause the shift.

What they do is get the ball rolling. A decrease in solar energy hitting the Arctic allows sea ice to form in winter and remain over summer, then to expand its reach the following year. The ice reflects more solar energy back to space. A colder ocean stores more CO2, which further dampens the greenhouse effect. Conversely, when ocean temperatures rise, more CO2 escapes into the atmosphere, where it traps more solar energy. With so many factors at play, each swing of the climate pendulum has produced its own unique conditions. Take, for example, the last interglacial, known as the Eemian, from 130 to 115,000 years ago. This happened at a time when CO2 was at preindustrial levels, and global temperatures had risen only modestly. But with higher solar energy striking the north, temperatures rose dramatically in the Arctic. The effect was amplified by the lower reflectivity of ice-free seas and spreading northern forests.

There is still uncertainty about how much these changes affected sea levels. Estimates range from a 5 to 9 meters, levels that would be catastrophic today. That’s one reason scientists today are intensively monitoring Earth’s frozen zones, including the ice sheet that covers Greenland. Satellite radar shows the flow of ice from the interior of the island and into glaciers. In the eastern part of the island, glaciers push slowly through complex coastal terrain. In areas of higher snowfall in the northwest and west, the ice speeds up by a factor 10. The landscape channels the ice into many small glaciers that flow straight down to the sea. In the distant past, the center of the island may have been drained by a giant canyon, recently discovered. Scientists found that it’s 550 kilometers long and up to 800 meters deep.

It leads from Greenland’s interior to one of today’s most volatile glaciers. This is the Petermann Glacier in Northwest Greenland. Amid unusually warm summer temperatures in 2012, satellites tracked a giant iceberg as it broke off and moved down the glacier’s outlet channel. At about 31 square kilometers, this island of ice stayed together as it floated along. After two months, it finally began to fragment. The Jakobshavn glacier on Greenland’s west coast flows toward the sea at a rapid rate of 20 to 40 meters per day. At the ice front, where the glacier meets the sea, Jakobshavn has been retreating as it dumps more and more ice into the ocean. You can see it in this map. In 1851, the front was down here. Now it’s 50 kilometers up. One reason, scientists say, is that water seeping down into its base is acting like a lubricant.

Another is that as the glacier thins, it’s more likely to break off, or calve, when it interacts with warmer ocean waters. Scientists are tracking the overall rate of ice loss with the Grace Satellite. They found that from 2003 to 2009, Greenland lost about a trillion tons, mostly along its coastlines. This number mirrors ice loss in the Arctic as a whole. By 2012, summer sea ice coverage had fallen to a little more than half of what it was in the year 1980. While the ice rebounded in 2013, the coverage was still well below the average of the last three decades. Analyzing global data from Grace, one study reports that Earth lost about 4,000 cubic kilometers of ice in the decade leading up to 2012. Sea levels around the world are now expected to rise about a meter by the end of the century. What will happen beyond that? To gauge the resilience of Greenland’s great ice sheet, scientists mounted one of the most intensive glacial drilling projects to date, the North Greenland Eemian Ice Drilling Project, or NEEM. The ice samples they obtained from the height of Eemian warming told a surprising story.

If you were a visitor to Northern Greenland in those times, you would have stood on ice over two kilometers thick. Temperatures were warmer than today by about 8 degrees Celsius. And yet, the ice had receded by only about 25%, a relatively modest amount. That has shifted the focus to Earth’s other, much larger ice sheet, on the continent of Antarctica. Antarctica contains 90% of all the ice, and 70% of all the fresh water on the Earth. Scientists are asking: how dynamic are its ice sheets? How sensitive are they to melting? Data from Grace and other satellites shows that this frozen continent overall has lately been losing as much ice as it gains. The vast plateau of Antarctic ice is one of the driest deserts on Earth. What little snow falls, remains, adding to the continent’s mass. You can see evidence of this in the snow and ice that piles up at the South Pole research station. This geodesic dome was built in the 1970s.

By the time it was decommissioned in 2009, the entrance was nearly buried. With a thickness of up to 4 kilometers, the ice on which this outpost sits will not melt easily. That’s true in part because of the landmass below it, captured in an extraordinary radar image. The eastern part of the continent, the far side of the image, is a stable foundation of continental crust. In contrast, the western side dips as much as 2500 meters below present day sea level. Along the Amundsen Sea Coast, the ice is disappearing at an accelerating rate. Inland ice streams are moving toward the ocean at at least 100 meters per year. They end up in floating ice shelves that extend hundreds of miles into the ocean. This region is the greatest source of uncertainty about global sea level projections. When ice shelves like this grow, they become prone to fracturing. A giant crack, for example, recently appeared in the Pine Island Glacier. Within two years, a 720 square kilometer iceberg had broken off.

But the scientists are more concerned about what’s happening below the surface. In recent times, the Southern ocean that swirls around the continent has been getting warmer, at the rate of .2 degrees Celsius per decade. That has affected ice shelves like Pine Island by melting them from below. In a comprehensive survey of the continent, scientists concluded that this process was responsible for 55 percent of the mass lost from ice shelves between 2003 and 2008. It’s also been blamed for one of the more puzzling twists in the story of climate change, the spread of sea ice all around Antarctica. One possibility is that ramped up winds, circling the pole, are pushing the ice into thicker, more resilient formations. Another is that the melting of ice shelves has spread a layer of cold, fresh water over coastal seas, which readily freezes.

A team of researchers has come to the Pine Island Glacier to try to monitor the melting in real time. After five years of preparation, they drilled through 500 meters of ice to begin measuring ice volume, temperature, salinity, and flow. In some places, they found melt rates of about 6 centimeters per day, or about 22 meters in a year. Because ice shelves hold back inland glaciers, the melting could trigger larger changes. That’s likely what happened to the Larsen ice shelf on the Antarctic Peninsula in the year 2002. It’s thought to have been stable since the last interglacial. Warmer ocean waters had been eating away at Larsen’s underside. By early February of 2002, the shelf began to splinter into countless small icebergs. By March 7th, when this picture was taken, it had completely collapsed, forming a vast slush that drifted out to sea. Without the shelf’s buttressing effect, a series of nearby glaciers picked up speed, dumping an additional 27 cubic kilometers of ice into the ocean per year.

Evidence from the last interglacial, the Eemian, brings an ominous warning of what could lie ahead. It’s based on the height of ancient coral reefs, which grow to a depth relative to the sea level above them. Based on reefs along the Australian coast, a recent study published in the journal Nature showed that sea levels remained stable for most of the Eemian, at 3-4 meters above those of today. But the authors found that in the last few thousand years of the period, starting around 118,000 years ago, sea levels suddenly shot up to 9 meters above today. The authors concluded, in their words, that “a critical ice sheet stability threshold was crossed, resulting in the catastrophic collapse of polar ice sheets.” Looking ahead, uncertainties about the future of our climate abound. According to one study, the long cool down to the next glacial period is due to start in the next 1500 years or so, based on the timing of Milankovic cycles. But for this actually to happen, the study says, enough new ice would have to form to get the ball rolling. CO2 would have to retreat to below pre-industrial levels.

Instead, it appears that a warming climate is becoming a fact of life. The danger is that if the melting gains a momentum of its own, even reducing CO2 emissions may not be enough to stop it. The still unfolding story of Earth’s past tells us about the mechanisms that can shape our climate. But it’s the unique conditions of our time that will determine sea levels, ice coverage, and temperatures. What’s at stake in the coming centuries is the world we know, the one that has nurtured and sustained us. The Earth itself will go on, ever changing on short and long time scales, a dynamic living planet 1.