17 INTO THE TROPOSPHERE

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    THANK GOODNESS FOR the atmosphere. It keeps us warm. Without it, Earth would be alifeless ball of ice with an average temperature of minus 60 degrees Fahre. In additiomosphere absorbs or deflects ining swarms of ic rays, charged particles,ultraviolet rays, and the like. Altogether, the gaseous padding of the atmosphere is equivalentto a fifteen-foot thiess of protective crete, and without it these invisible visitors fromspace would slice through us like tiny daggers. Even raindrops would pound us senseless if itweren’t for the atmosphere’s slowing drag.

    The most striking thing about our atmosphere is that there isn’t very much of it. It extendsupward for about 120 miles, which might seem reasonably bounteous when viewed fromground level, but if you shrank the Earth to the size of a standard desktop globe it would onlybe about the thiess of a couple of coats of varnish.

    For stifiveniehe atmosphere is divided into four unequal layers: troposphere,stratosphere, mesosphere, and ionosphere (now often called the thermosphere). Thetroposphere is the part that’s dear to us. It alone tains enough warmth and oxygen to allowus to fun, though even it swiftly bees ungenial to life as you climb up through it.

    From ground level to its highest point, the troposphere (or “turning sphere”) is about ten milesthick at the equator and no more than six or seven miles high iemperate latitudes wheremost of us live. Eighty pert of the atmosphere’s mass, virtually all the water, and thusvirtually all the weather are tained within this thin and wispy layer. There really isn’tmuch between you and oblivion.

    Beyond the troposphere is the stratosphere. When you see the top of a storm cloudflattening out into the classivil shape, you are looking at the boundary betweeroposphere and stratosphere. This invisible ceiling is known as the tropopause and wasdiscovered in 1902 by a Fren in a balloon, Léon-Philippe Teisserenc de Bort. Pause inthis sense doesn’t mean to stop momentarily but to cease altogether; it’s from the same Greekroot as menopause. Even at its greatest extent, the tropopause is not very distant. A fastelevator of the sort used in modern skyscrapers could get you there in about twenty mihough you would be well advised not to make the trip. Such a rapid ast withoutpressurization would, at the very least, result in severe cerebral and pulmonary edemas, adangerous excess of fluids in the body’s tissues. When the doors ope the viewingplatform, anyone inside would almost certainly be dead or dying. Even a more measuredast would be apanied by a great deal of disfort. The temperature six miles up be -70 degrees Fahre, and you would need, or at least very much appreciate,supplementary oxygen.

    After you have left the troposphere the temperature soon warms up again, to about 40degrees Fahre, thanks to the absorptive effects of ozone (something else de Bortdiscovered on his daring 1902 ast). It then pluo as low as -130 degrees Fahre inthe mesosphere before skyrocketing to 2,700 degrees Fahre or more ily  very erratic thermosphere, where temperatures  vary by a thousand degrees from dayto night—though it must be said that “temperature” at such a height bees a somewhatnotional cept. Temperature is really just a measure of the activity of molecules. At sealevel, air molecules are so thick that one molecule  move only the ti distance—aboutthree-millionths of an inch, to be precise—before banging into another. Because trillions ofmolecules are stantly colliding, a lot of heat gets exged. But at the height of thethermosphere, at fifty miles or more, the air is so thin that any two molecules will be milesapart and hardly <q></q>ever e in tact. So although each molecule is very warm, there are fewiioween them and thus little heat transferehis is good news for satellitesand spaceships because if the exge of heat were more effit any man-made objectorbiting at that level would burst into flame.

    Even so, spaceships have to take care ier atmosphere, particularly ourn trips toEarth, as the space shuttle bia demonstrated all tically in February 2003.

    Although the atmosphere is very thin, if a craft es in at too steep an angle—more thanabout 6 degrees—or too swiftly it  strike enough molecules to gee drag of anexceedingly bustible nature. versely, if an ining vehicle hit the thermosphere attoo shallow an a could well bounce bato space, like a pebble skipped across water.

    But you  veo the edge of the atmosphere to be reminded of what hopelesslyground-hugging beings we are. As anyone who has spent time in a lofty city will know, youdon’t have to rise too many thousands of feet from sea level before your body begins toprotest. Even experienced mountaineers, with the bes of fitness, training, and bottledoxygen, quickly bee vulnerable at height to fusion, nausea, exhaustion, frostbite,hypothermia, migraine, loss of appetite, and a great many other stumbling dysfuns. In ahundred emphatic ways the human body reminds its owhat it wasn’t desigo operateso far above sea level.

    “Even uhe most favorable circumstances,” the climber Peter Habeler has written ofditions atop Everest, “every step at that altitude demands a colossal effort of will. Youmust force yourself to make every movement, reach for every handhold. You are perpetuallythreatened by a leaden, deadly fatigue.” Iher Side of Everest, the British mountaineerand filmmaker Matt Dison records how Howard Somervell, on a 1924 British expeditionup Everest, “found himself choking to death after a piece of ied flesh came loose andblocked his windpipe.” With a supreme effort Somervell mao cough up theobstru. It turned out to be “the entire mucus lining of his larynx.”

    Bodily distress is notorious above 25,000 feet—the area known to climbers as the DeathZo many people bee severely debilitated, even dangerously ill, at heights of nomore than 15,000 feet or so. Susceptibility has little to do with fitness. Grannies sometimescaper about in lofty situations while their fitter offspring are reduced to helpless, groaningheaps until veyed to lower altitudes.

    The absolute limit of human tolerance for tinuous living appears to be about 5,500meters, or 18,000 feet, but even people ditioo living at altitude could not tolerate suchheights for long. Frances Ashcroft, in Life at the Extremes, hat there are Andean sulfurmi 5,800 meters, but that the miners prefer to desd 460 meters each evening andclimb back up the following day, rather than live tinuously at that elevation. People whohabitually live at altitude have oftehousands of years developing disproportionatelylarge chests and lungs, increasing their density of oxygen-bearing red blood cells by almost athird, though there are limits to how much thiing with red cells the blood supply stand. Moreover, above 5,500 meters even the most well-adapted women ot provide agrowius with enough oxygen t it to its full term.

    In the 1780s when people began to make experimental balloon asts in Europe,something that surprised them was how chilly it got as they rose. The temperature drops about3 degrees Fahre with every thousa you climb. Logic would seem to indicate thatthe closer you get to a source of heat, the warmer you would feel. Part of the explanation isthat you are not really getting he Sun in any meaningful sehe Sun is hreemillion miles away. To move a couple of thousa closer to it is like taking oepcloser to a bushfire in Australia when you are standing in Ohio, and expeg to smell smoke.

    The answer again takes us back to the question of the density of molecules imosphere.

    Sunlight energizes atoms. It increases the rate at which they jiggle and jounce, and in theirenliveate they crash into one another, releasi. When you feel the sun warm onyour ba a summer’s day, it’s really excited atoms you feel. The higher you climb, thefewer molecules there are, and so the fewer collisioween them.

    Air is deceptive stuff. Even at sea level, we tend to think of the air as beihereal and allbut weightless. In fact, it has plenty of bulk, and that bulk oftes itself. As a marinestist named Wyville Thomson wrote more than a tury ago: “We sometimes find whe up in the m, by a rise of an in the barometer, that nearly half a ton has beely piled upon us during the night, but we experieno invenience, rather a feeling ofexhilaration and buoyancy, si requires a little less exertion to move our bodies in thedenser medium.” The reason you don’t feel crushed uhat extra half ton of pressure is thesame reason your body would not be crushed deep beh t藏书网he sea: it is made mostly ofinpressible fluids, which push back, equalizing the pressures within and without.

    But get air in motion, as with a hurrie or even a stiff breeze, and you will quickly beremihat it has very siderable mass. Altogether there are about 5,200 million milliontons of air around us—25 million tons for every square mile of the pla—a notinseque<dfn></dfn>ntial volume. When you get millions of tons of atmosphere rushing past at thirty orforty miles an hour, it’s hardly a surprise that limbs snap and roof tiles go flying. As AnthonySmith notes, a typical weather front may sist of 750 million tons of cold air pinh a billion tons of warmer air. Hardly a wohat the result is at timesmeteically exg.

    Certainly there is no she of energy in the world above our heads. Ohuorm, ithas been calculated,  tain an amount of energy equivalent to four days’ use ofelectricity for the whole Uates. In the right ditions, storm clouds  rise to heightsof six to ten miles and tain updrafts and downdrafts of one hundred miles an hour. Theseare often side by side, which is why pilots don’t want to fly through them. In all, the internalturmoil particles within the cloud pick up electrical charges. For reasons irelyuood the lighter particles tend to bee positively charged and to be wafted by aircurrents to the top of the cloud. The heavier particles li the base, accumulatiivecharges. These ively charged particles have a powerful urge to rush to the positivelycharged Earth, and good luck to anything that gets in their way. A bolt of lightning travels at270,000 miles an hour and  heat the air around it to a decidedly crisp 50,000 degreesFahre, several times hotter than the surface of the sun. At any one moment 1,800thuorms are in progress around the globe—some 40,000 a day. Day and night across thepla every sed about a hundred lightning bolts hit the ground. The sky is a lively place.

    Much of our knowledge of what goes on up there is surprisingly ret. Jet streams, usuallylocated about 30,000 to 35,000 feet up,  bowl along at up to 180 miles an hour and vastlyinfluence weather systems over whole tis, yet their existence wasn’t suspected untilpilots began to fly into them during the Sed World War. Even now a great deal ofatmospheric phenomena is barely uood. A form of wave motion popularly known asclear-air turbulence occasionally enlivens airplane flights. About twenty suts a yearare serious enough to need rep. They are not associated with cloud structures oranything else that  be detected visually or by radar. They are just pockets of startlingturbulen the middle of tranquil skies. In a typical i, a plane en route fromSingapore to Sydney was flying over tral Australia in calm ditions when it suddehree hundred feet—enough to fling unsecured people against the ceiling. Twelve peoplewere injured, one seriously. No one knows what causes such disruptive cells<mark>..</mark> of air.

    The process that moves air around imosphere is the same process that drives theinternal engine of the pla, namely veoist, warm air from the equatorial regionsrises until it hits the barrier of the tropopause and spreads out. As it travels away from theequator and cools, it sinks. When it hits bottom, some of the sinking air looks for an area oflow pressure to fill and heads back for the equator, pleting the circuit.

    At the equator the ve process is generally stable and the weather predictably fair,but in temperate zohe patterns are far more seasonal, localized, and random, whichresults in an endless battle between systems of high-pressure air and low. Low-pressuresystems are created by rising air, which veys water molecules into the sky, f cloudsaually rain. Warm air  hold more moisture than cool air, which is why tropical andsummer storms tend to be the heaviest. Thus low areas tend to be associated with clouds andrain, and highs generally spell sunshine and fair weather. When two such systems meet, itoften bees ma in the clouds. For instaratus clouds—those unlovable,featureless sprawls that give us our overcast skies—happen when moisture-bearing updraftslack the oomph to break through a level of more stable air above, and instead spread out, likesmoke hitting a ceiling. Indeed, if you watch a smoker sometime, you  get a very goodidea of how things work by watg how smoke rises from a cigarette in a still room. Atfirst, it goes straight up (this is called a laminar flow, if you o impress anyone), and thenit spreads out in a diffused, wavy layer. The greatest superputer in the world, takingmeasurements in the most carefully trolled enviro, ot tell you what forms theseripplings will take, so you  imagihe difficulties that froeists whery to predict such motions in a spinning, windy, large-scale world.

    What we do know is that because heat from the Sun is unevenly distributed, differences inair pressure arise on the pla. Air ’t abide this, so it rushes around trying to equalizethings everywhere. Wind is simply the air’s way  to keep things in balance. Airalways flows from areas of high pressure to areas of low pressure (as you would expect; thinkof anything with air under pressure—a balloon or an air tank—and think how insistently thatpressured air wants to get someplace else), and the greater the discrepan pressures thefaster the wind blows.

    Ially, wind speeds, like most things that accumulate, grow expoially, so a windblowing at two hundred miles an hour is not simply ten times strohan a wind blowing attwenty miles an hour, but a huimes stronger—and hehat much more destructive.

    Introduce several million tons of air to this accelerator effed the result  be exceedinglyeic. A tropical hurrie  release iy-four hours as muergy as a rich,medium-sized nation like Britain or France uses in a year.

    The impulse of the atmosphere to seek equilibrium was first suspected by EdmondHalley—the man who was everywhere—and elaborated upon in the eighteenth tury by hisfellow Briton Gee Hadley, who saw that rising and falling ns of air teoproduce “cells” (known ever since as “Hadley cells”). Though a lawyer by profession, Hadleyhad a keen i in the weather (he was, after all, English) and also suggested a liween his cells, the Earth’s spin, and the apparent defles of air that give us our tradewinds. However, it was an engineering professor at the école Polyteique in Paris,Gustave-Gaspard de Coriolis, who worked out the details of these iions in 1835, andthus we call it the Coriolis effect. (Coriolis’s other distin at the school was to introducewatercoolers, which are still known there as Corios, apparently.) The Earth revolves at a brisk1,041 miles an hour at the equator, though as you move toward the poles the rate slopes offsiderably, to about 600 miles an hour in London or Paris, for instahe reason for thisis self-evident when you think about it. If you are on the equator the spinnih has tocarry you quite a distance—about 40,000 kilometers—to get you back to the same spot. If youstand beside the North Pole, however, you may ravel only a few feet to plete arevolutio in both cases it takes twenty-four hours to get you back to where you began.

    Therefore, it follows that the closer you get to the equator the faster you must be spinning.

    The Coriolis effect explains why anything moving through the air in a straight lierallyto the Earth’s spin will, given enough distance, seem to curve to the right in the northernhemisphere and to the left in the southern as the Earth revolves beh it. The standard wayto envision this is to imagine yourself at the ter of a large carousel and tossing a ball tosomeone positioned on the edge. By the time the ball gets to the perimeter, the target personhas moved on and the ball passes behind him. From his perspective, it looks as if it has curvedaway from him. That is the Coriolis effect, and it is what gives weather systems their curl andsends hurries spinning off like tops. The Coriolis effect is also why naval guns firingartillery shells have to adjust to left ht; a shell fired fifteen miles would otherwisedeviate by about a hundred yards and plop harmlessly into the sea.

    sidering the practical and psychological importance of the weather to nearly everyo’s surprising that metey didn’t really get going as a stil shortly before theturn of the eenth tury (though the term metey itself had been around since1626, when it was ed by a T. Granger in a book of logic).

    Part of the problem was that successful metey requires the precise measurement oftemperatures, and thermometers for a long time proved more difficult to make than you mightexpect. An accurate reading was depe oing a very even bore in a glass tube, andthat wasn’t easy to do. The first person to crack the problem was Daniel Gabriel Fahre, aDutch maker of instruments, who produced an accurate thermometer in 1717. However, forreasons unknown he calibrated the instrument in a way that put freezing at 32 degrees andboiling at 212 degrees. From the outset this numeric etricity bothered some people, and in1742 Anders Celsius, a Swedish astronomer, came up with a peting scale. In proof of theproposition that iors seldom get matters entirely right, Celsius made boiling point zeroand freezing point 100 on his scale, but that was soon reversed.

    The person most frequently identified as the father of moderey was an Englishpharmacist named Luke Howard, who came to promi the beginning of the eeury. Howard is chiefly remembered now fiving cloud types their names in 1803.

    Although he was an active and respected member of the Linnaean Society and employedLinnaean principles in his new scheme, Howard chose the rather more obscure AskesianSociety as the forum to announce his new system of classification. (The Askesian Society,you may just recall from an earlier chapter, was the body whose members were unusuallydevoted to the pleasures of nitrous oxide, so we  only hope they treated Howard’spresentation with the sober attention it deserved. It is a point on which Howard scholars arecuriously silent.)Howard divided clouds introups: stratus for the layered clouds, cumulus for thefluffy ohe word means “heaped” in Latin), and<cite></cite> cirrus (meaning “curled”) for the high,thihery formations that generally presage colder weather. To these he subsequentlyadded a fourth term, nimbus (from the Latin for “cloud”), for a rain cloud. The beauty ofHoward’s system was that the basipos could be freely rebio describe everyshape and size of passing cloud—stratocumulus, cirrostratus, cumulogestus, and so on. Itwas an immediate hit, and not just in England. The poet Johann vohe in Germany wasso taken with the system that he dedicated four poems to Howard.

    Howard’s system has been much added to over the years, so much so that the encyclopedicif little read Iional Cloud Atlas runs to two volumes, but iingly virtually all thepost-Howard cloud types—mammatus, pileus, nebulosis, spissatus, floccus, and mediocris area sampling—have never caught on with aside metey and not terribly muchthere, I’m told. Ially, the first, much thinion of that atlas, produced in 1896,divided clouds into ten basic types, of which the plumpest and most cushiony-looking wasnumber nine, cumulonimbus.

    1That seems to have been the source of the expression “to be oncloud nine.”

    For all the heft and fury of the occasional anvil-headed storm cloud, the average cloud isactually a benign and surprisingly insubstantial thing. A fluffy summer cumulus severalhundred yards to a side may tain no more thay-five or thirty gallons of water—“about enough to fill a bathtub,” as James Trefil has noted. You  get some sense of theimmaterial quality of clouds by strolling through fog—which is, after all, nothing more than acloud that lacks the will to fly. To quote Trefil again: “If you walk 100 yards through a typicalfog, you will e into tact with only about half a cubich of water—not enough togive you a det drink.” In sequence, clouds are not great reservoirs of water. Only about0.035 pert of the Earth’s fresh water is floating around above us at any moment.

    Depending on where it falls, the prognosis for a water molecule varies widely. If it lands iile soil it will be soaked up by plants or reevaporated directly within hours or days. If itfinds its way down to the groundwater, however, it may not see sunlight again for manyyears—thousands if it gets really deep. When you look at a lake, you are looking at acolle of molecules that have been there on average for about a decade. In the o theresideime is thought to be more like a hundred years. Altogether about 60 pert of1If you have ever been struck by how beautifully crisp and well defihe edges of cumulus clouds tend to be,while other clouds are more blurry, the explanation is that in a cumulus cloud there is a pronounced boundarybetween the moist interior of the cloud and the dry air beyond it. Any water molecule that strays beyond the edgeof the cloud is immediately zapped by the dry air beyond, allowing the cloud to keep its fine edge. Much highercirrus clouds are posed of ice, and the zoween the edge of the cloud and the air beyond is not soclearly delied, which is why they tend to be blurry at the edges.

    water molecules in a rainfall are returo the atmosphere within a day or two. Onceevaporated, they spend no more than a week or so—Drury says twelve days—in the skybefore falling again as rain.

    Evaporation is a swift process, as you  easily gauge by the fate of a puddle on asummer’s day. Even something as large as the Mediterranean would dry out in a thousandyears if it were not tinually replenished. Su event occurred a little under six millionyears ago and provoked what is known to sce as the Messinian Salinity Crisis. pened was that tial movement closed the Strait of Gibraltar. As the Mediterraneandried, its evaporated tents fell as freshwater rain into other seas, mildly diluting theirsaltiness—indeed, making them just dilute enough to freeze over larger areas than normal.

    The enlarged area of ice bounced back more of the Sun’s heat and pushed Earth into an iceage. So at least the theoes.

    What is certainly true, as far as we  tell, is that a little ge in the Earth’s dynami have repercussions beyond our imagining. Su event, as we shall see a little furtheron, may even have created us.

    Os are the real powerhouse of the pla’s surface behavior. Indeed, meteistsincreasingly treat os and atmosphere as a single system, which is why we must give thema little of our attention here. Water is marvelous at holding and transp heat. Every day,the Gulf Stream carries an amount of heat to Europe equivalent to the world’s output of coalfor ten years, which is why Britain and Ireland have such mild winters pared with adaand Russia.

    But water also warms slowly, which is why lakes and swimming pools are cold even oest days. For that reasoends to be a lag in the official, astronomical start of aseason and the actual feeling that that season has started. S may officially start ihern hemisphere in March, but it doesn’t feel like it in most places until April at the veryearliest.

    The os are not one uniform mass of water. Their differences in temperature, salinity,depth, density, and so on have huge effects on how they move heat around, whi turs climate. The Atlantic, for instance, is saltier than the Pacifid a good thing too. Thesaltier water is the de is, and deer sinks. Without its extra burden of salt, theAtlantic currents would proceed up to the Arctic, warming the North Pole but deprivingEurope of all that kindly warmth. The mai of heat transfer oh is what is knownas thermohaline circulation, which inates in slow, deep currents far below the surface—aprocess first detected by the stist-adventurer t von Rumford in 1797.

    2What happensis that surface waters, as they get to the viity of Europe, grow dense and sink to greatdepths and begin a slow trip back to the southern hemisphere. When they reatarctica,they are caught up iarctic Circumpolar Current, where they are driven onward intothe Pacific. The process is very slow—it  take 1,500 years for water to travel from the2The term means a number of things to different people, it appears. In November 2002, Carl WunsITpublished a report in Sce, &quot;What Is the Thermohaline Circulation?,&quot; in which he hat the expressionhas been used in leading journals to signify at least seven different phenomena (circulation at the abyssal level,circulation driven by differences iy or buoyancy, &quot;meridional overturning circulation of mass,&quot; and soon)-though all have to do with o circulations and the transfer of heat, the cautiously vague and embragsense in which I have employed it here.

    North Atlantic to the mid-Pacific—but the volumes of heat and water they move are verysiderable, and the influen the climate is enormous.

    (As for the question of how anyone could possibly figure out how long it takes a drop ofwater to get from one o to ahe answer is that stists  measure poundsier like chlorofluorocarbons and work out how long it has been sihey were lastin the air. By paring a lot of measurements from differehs and locations they reasonably chart the water’s movement.)Thermohaline circulation not only moves heat around, but also helps to stir up nutrients asthe currents rise and fall, making greater volumes of the o habitable for fish and othermarine creatures. Unfortunately, it appears the circulation may also be very sensitive toge. Acc to puter simulations, even a modest dilution of the o’s salttent—from increased melting of the Greenland ice sheet, for instance—could disrupt thecycle disastrously.

    The seas do oher great favor for us. They soak up tremendous volumes of carbon andprovide a means for it to be safely locked away. One of the oddities of our solar system is thatthe Sun burns about 25 pert more brightly now thahe solar system was young.

    This should have resulted in a much warmer Earth. Indeed, as the English geologist AubreyManning has put it, “This colossal ge should have had an absolutely catastrophic effe the Earth a appears that our world has hardly been affected.”

    So what keeps the world stable and cool?

    Life does. Trillions upon trillions of tiny marine anisms that most of us have neverheard of—foraminiferans and coccoliths and calcareous algae—capture atmospheric carbon,in the form of carbon dioxide, when it falls as rain and use it (in bination with otherthings) to make their tiny shells. By log the carbon up in their shells, they keep it frombeing reevaporated into the atmosphere, where it would build up dangerously as a greenhousegas. Eventually all the tiny foraminiferans and coccoliths and so on die and fall to the bottomof the sea, where they are pressed into limesto is remarkable, when you behold araordinary natural feature like the White Cliffs of Dover in England, to reflect that it ismade up of nothing but tiny deceased marine anisms, but even more remarkable when yourealize how much carbon they cumulatively sequester. A six-inch cube of Dover chalk willtain well over a thousand liters of pressed carbon dioxide that would otherwise bedoing us no good at all. Altogether there is about twenty thousand times as much carbonlocked away in the Earth’s rocks as imosphere. Eventually much of that limestone willend up feeding voloes, and the carbon will return to the atmosphere and fall to the Earth inrain, which is why the whole is called the long-term carbon cycle. The process takes a verylong time—about half a million years for a typical carbon atom—but in the absence of anyother disturba works remarkably well at keeping the climate stable.

    Unfortunately, human beings have a careless predile for disrupting this cycle byputting lots of extra carbon into the atmosphere whether the foraminiferans are ready for it ornot. Since 1850, it has beeimated, we have lofted about a hundred billion tons of extracarbon into the air, a total that increases by about seven billion tons each year. Overall, that’snot actually all that muature—mostly through the belgs of voloes and the decayof plants—sends about 200 billion tons of carbon dioxide into the atmosphere each year,nearly thirty times as much as we do with our cars and factories. But you have only to look atthe haze that hangs over our cities to see what a difference our tribution makes.

    We know from samples of very old ice that the “natural” level of carbon dioxide imosphere—that is, before we started inflating it with industrial activity—is about 280 partsper million. By 1958, when people in lab coats started to pay attention to it, it had risen to 315parts per million. Today it is over 360 parts per million and rising by roughly one-quarter of 1pert a year. By the end of the twenty-first tury it is forecast to rise to about 560 partsper million.

    So far, the Earth’s os and forests (which also pack away a lot of carbon) have mao save us from ourselves, but as Peter Cox of the British Meteical Office puts it:

    “There is a critical threshold where the natural biosphere stops buffering us from the effects ofour emissions and actually starts to amplify them.” The fear is that there would be a runawayincrease in the Earth’s warming. Uo adapt, many trees and other plants would die,releasing their stores of carbon and adding to the problem. Such cycles have occasionallyhappened in the distant past even without a human tribution. The good news is that eveure is quite wonderful. It is almost certain that eventually the carbon cycle wouldreassert itself aurn the Earth to a situation of stability and happiness. The last time thishappened, it took a mere sixty thousand years.

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