Life

by Tim Flannery

  So you might be surprised to learn that temperatures remain cold—indeed they are cooling—over the highest parts of both the Greenland and Antarctic ice domes. These are the only places on Earth where significant negative temperature trends are occurring. This is comforting, for a recent study has concluded that should the Greenland ice cap ever melt it would be impossible to regenerate it, even if our planet’s atmospheric CO2 was returned to pre-industrial levels.4

  The greatest extent of ice in the Northern Hemisphere is the sea ice covering the polar sea, and since 1979 its extent in summer has contracted by 20 per cent. Furthermore the remaining ice has greatly thinned. Measurements taken using submarines reveal that it is only 60 per cent as thick as it was four decades earlier. This prodigious melting, however, has no direct consequence for rising seas, any more than the melting ice cube in a glass of scotch raises the level of liquid in the glass. This is because the Arctic ice cap is sea ice, nine-tenths of which is submerged, and when it melts it condenses into water in precisely the same proportion as it projected from the sea. Only land ice, as it melts and runs into the sea, adds to sea levels.

  Although the melting of sea ice has no direct effect, its indirect effects are important. At its current rate of decline, little if any of the Arctic ice cap will be left by the end of this century, and this will significantly change the Earth’s albedo. Remember, one-third of the Sun’s rays falling on Earth is reflected back to space. Ice, particularly at the Poles, is responsible for a lot of that albedo, for it reflects back into space up to 90 per cent of the sunlight hitting it. Water, in contrast, is a poor reflector. When the Sun is overhead it reflects a mere 5 to 10 per cent of light back to space, though, as you may have noticed while watching a sunset by the sea, the amount of light reflected off water increases as the Sun approaches the horizon. Replacing Arctic ice with a dark ocean will result in a lot more of the Sun’s rays being absorbed at Earth’s surface and re-radiated as heat, creating local warming which, in a classic example of a positive feedback loop, will hasten the melting of the remaining continental ice.

  As recently as 2001, rising seas looked to be one of the least pressing problems confronting humanity as a consequence of climate change, for over the preceding 150 years the oceans had only risen by ten to twenty centimetres, which amounts to 1.5 millimetres per year—around a hundredth as fast as your hair grows.5 Over the last decade of the twentieth century, however, the rate of sea level rise doubled to around three millimetres per year. Scientists are concerned at the momentum of the rise, for the sea is the greatest juggernaut on our planet, and when movements within it reach a certain pace, all the effort of all the people on Earth can do nothing to slow it.

  The oceans, of course, are massive when compared with the atmosphere, having 500 times the mass, and they are very dense. So when we think of the atmosphere changing the oceans, we must imagine something like a VW Beetle pushing a tank down a slope. It takes effort to get the monster moving, but when it does shift there’s little the Beetle can do to alter the tank’s trajectory. Another factor important in slowing the oceans’ reaction to climate change is the stratification of its waters. If all the oceans’ water was homogenised to one temperature, it would be a chilly 3.5°C. Away from the Poles the oceans’ upper layers are far warmer, but they become ever cooler until, in the depths (because the water is salty), the temperature can be below freezing point.

  Any cooling of the surface helps the water layers to mix, thus speeding the cooling process. As the oceans warm they become more stratified, and as a result water mixing from the surface to the depths is impeded so that it takes a long time for the heat to finds its way to the abyssal plain kilometres below.6 This means that when Earth is on a cooling trend, there is little lag between the reduction of greenhouse gases and the changed climate they entail. When our planet is heating, however, it takes the surface layers of the oceans about three decades to absorb heat from the atmosphere, and a thousand years or more for this heat to reach the ocean depths; all of which means that—from the perspective of global warming—the oceans are still living in the 1970s.

  Despite this great inertia, rises in temperature are occurring at the surface of the oceans, and information is also emerging for a sharp rise in temperature at depth.7 There is nothing we can do to prevent this slow transfer of heat from air to sea, which is very bad news, for the heat acts in two ways to cause rising of the waters.

  When most of us think of a rising sea, we imagine melting glaciers and ice caps pouring into the oceans. Over the past century, however, much of the sea level rise has come from an expansion of the oceans, for warm water occupies more space than cold. This ‘thermal expansion’ of the oceans is expected to raise sea levels by 0.5 to 2 metres over the next 500 years. In 2001 the Intergovernmental Panel on Climate Change estimated that (in round figures) the oceans would rise a mere ten centimetres to a metre over this century. Thermal expansion, they suggested, would contribute between ten and forty-three centimetres of this rise, while melting mountain glaciers would add up to twenty-three centimetres more, mostly from the melting of non-polar glaciers and from Greenland.

  In the late 1990s, when the panel was compiling its report, the rate of melting of many glaciers was not known, and the situation around the South Pole was particularly uncertain. Heroic scientific efforts have now yielded new data, making the science of sea-level change one of the fastest moving aspects of climate science. Typical of this new generation of studies is one published by Eric Rignot of the Jet Propulsion Laboratory, Pasadena, and his collaborators.8 They measured the melt-rate of the Patagonian ice fields—the largest temperate ice masses in the Southern Hemisphere—and found that they are contributing more water per unit area to global sea level rise (0.1 mm per year) than even the gigantic glaciers of Alaska.

  But it’s Antarctica that provides the most alarming news of melting ice. By 2004 one scientific report after another was crowding the pages of learned journals with news of ominous changes to the ice of the Antarctic Peninsula and adjacent areas. These studies make clear that a great domino effect—wherein the destabilisation of one ice field leads to the destruction of a neighbour—is playing itself out at the southern extremity of the world. Because the decline is affecting ever-larger expanses of ice, it is becoming evident that melting polar ice will be by far the greatest contributor to a rising sea in coming decades.

  The first dramatic indications that all was not well came in February 2002 when the Larsen B ice shelf—at 3250 square kilometres it was the size of Luxembourg—broke up over a matter of weeks. Although scientists knew that the Antarctic Peninsula was warming more rapidly than almost anywhere else on Earth, the speed and abruptness of Larsen B’s collapse shocked many. In the aftermath, scientists learned that there was an important and hitherto overlooked exception to the rule that melting of sea ice does not affect sea levels. Almost immediately after the breakup, the glaciers that fed into the now fragmented ice sheet began to flow more rapidly. Glaciers, of course, flow much more slowly than rivers. Yet they do flow, and the collapse of Larsen B demonstrated forcefully that one of the most important features determining glaciers’ speed is the extent of ice at their mouth. A thick ice sheet acts much like a dam, slowing the flow of the glacial ice to the sea, thereby restricting its rate of melting. Remove the ice plain and the glacier speeds up.

  It’s difficult and expensive to study Antarctica’s glaciers and ice sheets, but the fate of the Larsen B soon had researchers looking both at the details of its demise and at other ice shelves in the region. In 2003 a study summarising a decade of satellite data revealed the ultimate cause of Larsen’s collapse. Summer melting at both the top and the bottom of the ice sheet, brought about by warming of both the atmosphere and the ocean, had so thinned it and riven it with crevasses that its destruction was inevitable.9 But melting of the ice from below was the most important factor. While the Weddell Sea’s deep waters, which flow past the ice, were still cold enough to kill a pe
rson in minutes, they had warmed by 0.32°C since 1972, and this change was enough to initiate the melting.10

  Scientists are convinced that sometime this century the rest of the Larsen ice shelf will break up, but by then our attention will be gripped by the fate of far greater ice-masses.11 The first to enter our consciousness is likely to be the Amundsen ice plain, an extensive area of sea ice off the coast of West Antarctica. In late 2002 a team of scientists led by NASA researchers discovered that it was thinning rapidly. In their study, published in October 2004, they reported that large sections of the ice plain had become so thin that they were nearing a point that could allow them to float free of their ‘anchors’ on the ocean bed and collapse like Larsen B.12 The fatal moment for the Amundsen, they ventured, could be as little as five years off, for already its thinning had led to a quickening of glacial flow. At the time of the survey, the glaciers feeding into the Amundsen had increased their rate of discharge to around 250 cubic kilometres of ice per year—enough to raise sea levels globally by 0.25 of a millimetre per annum. As there is enough ice in the glaciers feeding into the Amundsen Sea to raise global sea levels by 1.3 metres, their increasing rate of flow, and the incipient break-up of their ice-plain ‘brake’, are of concern to everyone.

  Across the Antarctic Peninsula lies one of the world’s largest surviving expanses of sea ice. The West Antarctic ice sheet is also tenuously anchored to the bottom of a shallow sea. The possibility that it may destabilise was raised back in the 1970s, when University of Ohio glaciologist John Mercer pointed out the similarities between it and the Eurasian Arctic. Both regions, he noted, are shallow seas of similar topography that do (or did) support vast ice sheets. The ice sheets of the Eurasian Arctic broke up in spectacular fashion between 15,000 and 12,000 years ago and Mercer worried that, as a result of global warming (something which was then almost unheard of ), the West Antarctic ice sheet may soon do the same thing.13

  It was recently discovered that the West Antarctic ice sheet is bounded by rapidly moving ‘ice streams’ that flow over gravels which, in certain circumstances, facilitate their flow.14 Just how difficult it is to measure the rate of flow of these ‘streams’ was demonstrated by a two-week study of the Whillans ice stream. It was long thought to be stable—indeed it was thought to be slowing in its rate of flow—which would have been a good sign for stability of the ice sheet overall. Yet the study revealed that it could move at the extremely rapid rate—for ice, at least—of one metre per hour! This, however, only occurred when the tide was right; when it wasn’t, the ice stream stopped.15 With the ice stream so finely balanced, it’s easy to see how rising sea levels or thinning ice might make rapid flow permanent.

  If the West Antarctic ice sheet ever does detach itself from the sea floor, it would add sixteen to fifty centimetres of sea level rise by 2100. Even worse, the glaciers feeding into it would accelerate, adding much more to sea levels. In all, the 3.8 million cubic kilometres of sea and glacial ice contained and held back by the West Antarctic ice sheet comprise enough water to raise global sea levels by six to seven metres.

  There is one bright spot in all of this. The increased precipitation occurring at the Poles is expected to bring more snow to the high Antarctic ice cap, which may compensate for some of the ice being lost at the continent’s margins, though just how much compensation this will bring, and for how long, is currently unknown.

  So swift have been the changes in ice-plain science, and so great is the inertia of the oceanic juggernaut, that climate scientists are now debating whether humans have already tripped the switch that will create an ice-free Earth. If so, we have already committed our planet and ourselves to a rise in the level of the sea of around sixty-seven metres. The next great question would be, how long will it take for the ice to melt? Many scientists think that, regardless of the amount of melting in store, the bulk of the sea level rises will occur after 2050, and it will take millennia for all of the ice to melt. Still, some scientists are predicting a rise in sea levels of three to six metres over a century or two.16

  Predicting the future has never been humanity’s strong suit, but with technological advances made over two decades—including satellite surveillance data of changes at the surface of our planet, better computers, and a firm grasp of Earth systems such as the carbon cycle—scientists have been able to build virtual worlds to see the approximate shape of things to come, and how things might stand if we change our ways. These wondrous new playthings of science have much to tell us about our climatic future over coming decades.

  PART IV

  A Fresh Look at Earth

  2010–2017

  A Fresh Look at Earth

  2010

  Big ball of iron with some rock on the outside and a very very thin coating of moisture and oxygen and dangerous creatures.

  A DESCRIPTION OF EARTH, WIKIPEDIA

  WHAT IS LIFE? Is it separable from Earth? At the most elemental level, we living beings are not even properly things, but rather processes. A dead creature is in every respect identical to a live one, except that the electrochemical processes that motivate it have ceased. Life is a performance—heavens’ performance—which is fed and held in place, and eventually extinguished, by fundamental laws of chemistry and physics. Another way of thinking about life is that we are all self-choreographed extravaganzas of electrochemical reaction, and it is in the combined impacts of those reactions, across all of life, that Gaia itself is forged.

  Thinking of life as something separate from Earth is wrong. A striking instance concerns the origins of diamonds. Analysis shows that many diamonds are made from living things. Tiny organisms adrift on an ancient sea took in carbon from the atmosphere, then died and sank into the abyss. From there geological processes carried the carbon into the Earth’s very mantle, subjecting it to unimaginable heat and pressure, thereby transforming it into diamonds. Eventually these were shot back to the surface in great pipes of molten rock, and today some grace our fingers.1

  Our planet formed some 4.5 billion years ago as a result of a ‘gravitational instability in a condensed galactic cloud of dust and gas’.2 It formed in an astonishingly short time, perhaps as little as 10 million years, and critically important qualities were added when a heavenly body the size of Mars struck the proto-Earth, liquefying it and ejecting from it a mass destined to become the Moon. The liquefied remainder then began to differentiate into a metallic core, making up almost 30 per cent, a silicate mantle making up almost 70 per cent, and a thin crust making up just 0.5 per cent. Within a billion years, or perhaps just a few hundred million years, parts of that crust had begun to organise into life.

  That was so long ago that the Moon was far closer than it is today, and was replete with active volcanoes. It loomed large in the sky, and exerted such gravitational pull that Earth’s crust buckled many metres with each tidal swing. It challenges our imagination to think of microscopic portions in that ancient crust slowly becoming living things, and indeed how the spark of life was first kindled remains one of science’s great mysteries. But there is no doubt that the electrochemical processes that are life are entirely consistent with an origin in Earth’s crust—our very chemistry tells us that we are, in all probability, of it. This concept of life as living Earthly crust challenges the dignity of some. It should not. We have long understood, from biblical teaching and practical experience, that we are naught but earth: ashes to ashes, dust to dust, as the English burial service puts it. Indeed, ‘dust thou art, and unto dust shalt thou return’ are among the oldest written words we have.3

  The building blocks of life, however, go back even further than the formation of our planet. The elements that form us, the carbon, phosphorus, calcium and iron to name but a few, were created in the hearts of stars. And not just in one generation of stars, for it takes the energy of three stellar generations combined to form some of the heavier elements, such as carbon, that life finds indispensible. Stars age very slowly, and to complete three generations takes almost
all of time—from the Big Bang to the formation of Earth. We are, as the astrophysicist Carl Sagan said, mere stardust, but what a wondrous thing that is.

  Earth’s crust may seem like a passive organ, a mere substrate, but it has been profoundly influenced by life, and it is the sheer size of life’s energy budget (the total amount of energy living things capture from the Sun) that makes this possible. Plants capture the Sun’s energy using photosynthesis. Inside green leaves lie tiny structures, called chloroplasts, which use the energy of sunlight to break apart molecules of CO2 which, if they were not so dealt with, would eventually make up most of Earth’s atmosphere. Plants use the CO2 to form organic compounds, which in turn are used to build bark, wood and leaves—indeed all the tissues of the plants around us. Look at a tree and what you see is mostly congealed carbon, a tonne of dry wood being the result of the destruction, by photosynthesis, of around two tonnes of atmospheric CO2.