Climate Change

The Earth’s climate is part of an ecological system which, despite spinning in cold space, manages to regulate its temperature and support life. Its ability to do so is shaped by three things:

1. Endowment: the physical properties of the Earth—its size and distance from the sun and moon; its continents and oceans; its life; the composition of gases; the laws of physics; the whole of its inheritance; the story so far.

2. Internal dynamics: the way in which the many parts of the system interact, with diversity and ingenuity.

3. Forcings: changes which are imposed from “outside”. But what “outside” means is, of course, rather arbitrary, since it could reasonably be argued that most are part of Gaia. So here it is simply affirmed that forcings consist of changes in the intensity of radiation from the sun; emissions of greenhouse gases arising from human activity; other human assaults on Gaia, such as the destruction of forests; and (a rare but spectacular forcing) meteorite strikes. Volcanic activity and discharges of methane are also taken to be forcings.^C92

The story of climate change in our time is one in which a massive intervention—a forcing—is in progress in the form of an imposed change to the composition of the atmosphere. The Earth’s ability to get rid of excess heat is being damaged, with results that—if left unrepaired—will be as destructive to the planet’s present ecology as a breakdown in the removal of waste heat would be to any other living system.

The greenhouse gases which are responsible for this take their name from the key property of the glass in a greenhouse: it is transparent to short-wave radiation from the sun, but not to the long wave radiation (heat) that is generated when the sunlight comes into contact with material objects such as dust particles, water, vegetation or the ground. Greenhouse gases keep heat in. In small quantities, they do an essential job since, without them, Earth would be too cold to support life. But, like any other good thing, you can have too much of it. The greenhouse gases that are the unintended consequence of industrial civilisation are present in excess.^C93

The six main greenhouse gases are these:^C94

• Carbon dioxide (CO₂), which is long-lived in the atmosphere, is the most important of the greenhouse gases. About half of the CO₂ emitted by man is quickly removed by fast processes such as photosynthesis. Other removal processes, such as absorption by the oceans, work on longer timescales, and the timescale for removal by weathering of rocks is longer still, so that some 20 percent remains in the atmosphere for thousands of years. Carbon dioxide is the product of combustion, respiration and decay; the default chemical that remains when the complex organic compounds from which life is made have broken down.^C95

Carbon itself is the defining element of organic chemistry—the chemistry of life—but (relative to the total quantity on the planet) the amount of carbon that actually participates in the living stages of the carbon cycle at any one time is minute. The great majority of it is safely stored out of the way in the rocks that, for the past four billion years, have by various means bonded it into their structures. Some of it is in more recent deposits of oil and gas. The quantity of carbon in the form of carbon dioxide that remains free in the atmosphere is tightly limited and regulated by the ecosystem, whose most powerful instrument is photosynthesis by plants and algae in their various forms, on land and in the oceans. In excess, carbon dioxide would spell the death of the planet. The atmosphere of Venus, being thick with it (but also closer to the sun), scorches at a temperature of 450°C.^C96

• Methane (CH₄) is made when organic matter is decomposed by microorganisms in places which are both wet and low in oxygen, such as peat bogs, the guts of ruminants (e.g., cows) and decomposing forests on their way to becoming coal. There are very large quantities of methane frozen into the permafrost of the land and seabed of the high latitudes, buried in the peat bogs, or lying undisturbed in crystalline form in sea beds round the world. Generally, it stays put. The last time the Earth’s methane was released in substantial quantities, some 251 million years ago, it raised the temperature so much, and turned the oceans so acid, that 95 percent of the species in existence on the planet at that time became extinct. This was the third Great Extinction—the Permian Extinction, the biggest of them all, coming statistically close to a complete elimination of life. If the permafrost of our own time were to thaw, in turn warming the sea by the few degrees needed to destabilise the crystals, methane would pour into our atmosphere, raising the temperature as it did so. That is not happening, as yet, on a scale which compares with the Third Extinction, but there is an amplifying feedback here—methane emissions warm the atmosphere, causing more methane emissions—and the current rate of species decline is on a path which already has some scientists describing our own epoch as “The Sixth Extinction”.^C97

Methane has only a short life in the atmosphere—half the methane emitted will be gone within twelve years, broken down to CO₂ and water—and much less methane (relative to carbon dioxide) is released into the atmosphere from human activities. And yet, a released tonne of methane has some 72 times the warming impact of a released tonne of carbon dioxide, over the first 20 years. Measured over 100 years, the climate impact is about 25 times that of the same mass of carbon dioxide. After taking all these factors into account, the Intergovernmental Panel on Climate Change (IPCC) estimates that the radiative forcing (total contribution to global warming) of anthropogenic methane emissions (i.e., those arising from human activity) is currently about 29 percent of that of carbon dioxide.^C98

• Nitrous oxide (N₂O)’s main anthropogenic source is from agriculture, including the use of nitrogen fertiliser, biomass-burning and cattle-raising, and industrial processes such as the production of nylon.

It has a lifetime of about 114 years in the atmosphere. Over 100 years the global warming potential of a tonne of nitrous oxide is about 298 times that of a tonne of carbon dioxide, but it is released in small quantities, and the IPCC estimates that its net impact is about 10 percent of that of carbon dioxide.^C99

• Halogenated compounds are synthetic chemicals in which one or more of the carbon atoms they contain is bonded with a halogen—chlorine, fluorine, bromine or iodine. Their stability makes them useful for pesticides (e.g., organochlorates), for the enrichment of nuclear fuel (uranium hexafluoride), and for refrigerants such as CFCs. Some halogenated compounds are now prohibited, notably CFCs and HFCs, because of the damage they do to the ozone layer, but they are long-lived, and those which were not listed in the 1988 rules on ozone depletion are still widely-used.

The global warming potential of these compounds is generally high—for example, HFC-23 has an expected life in the atmosphere of 270 years, and its global warming potential per kilogram, measured over 100 years, is about 14,800 times that of carbon dioxide—but they are released in low quantities, and the IPCC estimates a net impact of about 20 percent of that of carbon dioxide.^C100

• Ozone (O₃) in the lower atmosphere (tropospheric ozone) is a by-product of highly-energetic reactions such as photocopying and the combustion of fossil fuels, and of the action of sunlight on carbon dioxide, solvents and nitrous oxide. It has a life of only a few days, and its effects on the climate depend (for instance) on where it is, and its interactions with methane. The IPCC estimates that, overall, its impact is about 20 percent of that of carbon dioxide.^C101

• Water vapour (H₂O) is a significant greenhouse gas. The amount in the atmosphere depends mainly on the temperature, so that it has a gearing (amplifying/positive feedback) effect: the greater the warmth produced by atmospheric carbon dioxide, the greater the evaporation from the oceans, which tends to raise the temperature yet further. And the presence of water vapour in the atmosphere also affects the formation of clouds, whose impact on the climate is complex—both cooling (since clouds provide shade) and warming (since they keep the heat in).

In fact, both sides of the equation of forces which control atmospheric carbon dioxide levels (concentrations) are in trouble. Carbon is being emitted at the rate of about 8.7 billion tonnes per year (32 billion tonnes of carbon dioxide) by the burning of the fossil fuels (oil, gas and coal), with additions from the burning of forests and the draining of peat bogs; at the same time, the ‘sinks’ which take it out of the atmosphere (such as absorption by plants and oceans) are diminishing.^C102

Throughout the history of the Earth, the quantity of carbon dioxide in the atmosphere has varied widely and often, but there has been a pattern to it. Since the beginning of the more recent “ice ages” starting some 2.9 million years ago—actually a series of ice ages and interglacials, with each cycle lasting some 100,000 years—the quantity has been about 400 billion tonnes during the cold periods (the glaciations), and 600 billion tonnes during the warm periods (the interglacials). But that long-lived oscillation between deep cold and tolerable warmth may now have ended for a time. There are now more than 800 billion tonnes of carbon dioxide in the atmosphere, and rising.^C103

For the last twenty years, the implications of all this have been monitored in detail by the Intergovernmental Panel on Climate Change. It was set up in 1988, and it has published major bodies of work—its Assessment Reports—in 1990, 1995, 2001 and 2007: landmark studies with wide (unpaid) participation. Now, time-lags are inevitable between the time of a scientific advance and the time when it is considered suitable for publication in a report. Often, the most important insights are those which it is hardest to be certain about, and which may take many years to bring up to the level of verification which the IPCC ranks as “very likely”, or justifying “high confidence”. There is therefore a conservative bias in its work, but it nonetheless sets a standard and provides a common point of reference.^C104

In its 2007 report, the IPCC supplied estimates of the reduction in global emissions of carbon dioxide that would be required to maintain concentrations in the atmosphere within approximately the range in which we are now—350–400 parts per million (ppm). In order to achieve this, the IPCC finds that emissions of carbon dioxide would have to peak by 2015 and be reduced by between 50% and 85% (relative to 2000 levels) by 2050. The report adds that, even if this were achieved, the global mean temperature of the planet would continue to rise from the present 0.8°C above the pre-industrial equilibrium level, eventually settling at a new long-term equilibrium between 2°C and 2.4°C hotter.^C105

We have a comment on the implications of temperature rise from the climate scientist James Hansen. Hansen’s projections of the consequences are not shared by the majority of climate scientists, but they do tell us something about the range of possibilities being debated at present:

Global warming of 2–3°C above the present temperature [i.e., 2.8–3.8°C above pre-industrial levels] would produce a planet without Arctic sea-ice, a catastrophic sea level rise in the pipeline of around 25 metres, and a super drought in the American West, southern Europe, the Middle East and parts of Africa.^C106

Now, it is for the reader of the IPCC’s work to make his or her own judgment about its conclusions on the temperature rises in prospect. The starting point is to note that the IPCC’s work is based on a combination of good data and good modelling. Its quality is explicitly discussed in the report, which gives three reasons to believe that the modelling is sound. First, it is based on established physical laws, such as the conservation of mass, energy and momentum, along with a wealth of observations. Secondly, it can predict events in the present climate in some detail, such as monsoon patterns and regional changes in temperature and pressure. Thirdly, the modelling performs well not only when it is asked to reproduce the essential features of the climate in the recent past, but also, in broad terms, older changes such as ocean temperatures during the last glaciation. The modelling is criticised by climate contrarians on the grounds that the science is biased by political pressure, by the system of grants that are more available to research which shows that there is a problem than to research that concludes that everything is just fine, and by the money to be made out of responses such as international carbon credits. It would be surprising if climate science were an exception to the rule that everything that can be exploited will be exploited, but the field of climate and paleoclimate is one of the most brilliant and necessary that has been opened up by science, and this is reflected in the modelling and in the current imperfect but impressive understanding of our planet as a dynamic living system.^C107

And yet, there is a problem here. The problem is not that the models may be exaggerating the changes in prospect, but that they may be underestimating them. Here are three things to consider:

1. Feedbacks

There can be positive (amplifying) and negative (damping) feedbacks in any system, where each effect knocks on to other effects which intensify, or reduce, the consequences. Negative feedbacks in the climate system include the stimulating effect of higher levels of CO₂ on the growth of plants, and the rise in the amount of dust in the atmosphere—produced by industrial activity, drought and loss of vegetation—reducing the amount of sunlight that penetrates. But such effects are recognised to be short-lived: the effect of CO₂ on plants peaks, easing off as concentrations rise, and the dust would clear after a week or two if industrial activity were to cease. The feedbacks that are most evident and likely to have the greatest impact are positive feedbacks.^C108

Positive feedbacks are difficult to model. First, there are a lot of them, and they include events which no one has thought of, and about which we know little. One example is the recent realisation that, as the ice sheets of Greenland melt, water pours down to the bed rock, creating a slippery surface which could enable very large sheets of ice to slide off into the sea, so that the melting of Greenland could unfold much faster than had been thought.

Secondly, there is the problem of “second-order” feedbacks, where one feedback triggers another which intensifies the first, or where it triggers several more, producing a range of feedbacks so complex that the difficulty of modelling rises exponentially. This is a familiar problem with drug testing: one drug can be tested in a straightforward way, but when it is tested for interaction with other drugs, things get complicated. If each drug had to be tested against all the other treatments or foods to which a patient might be exposed, the permutations would increase exponentially, quickly exceeding the budget of any company (or the scope of any model). In the case of drugs the risk is more tolerable because the consequences of an unexpected interaction are individual, rather than global.

Here are some examples of feedbacks. No doubt all of them have been programmed into climate models somewhere, but the emergence of consensus about how severe they are, what the second-order feedbacks will be, and how they interact, could take some time:

• Ocean temperatures and mixing. At temperatures above 4°C, the specific gravity of water declines (the water becomes lighter). As a consequence, a layer of warmer water tends to rise and form at the surface of the ocean; this layer is then further warmed by sunlight and so becomes increasingly stable. This stability weakens the circulation of carbon-dioxide-rich water from the surface to the colder, deeper layers. But water that is already relatively saturated with CO₂ absorbs less CO₂ from the air. So the direct absorption of carbon dioxide from the atmosphere by the surface of the oceans is becoming less efficient as the temperature rises.^C109

• Ocean nutrients. A related effect of that warmer surface layer is that it prevents nutrient-rich water from the depths reaching the surface where it could support a population of plankton. Plankton are to oceans as grass is to meadows: when the surface water becomes sterile, plankton’s vital role in absorbing carbon dioxide is not done.^C110

• Acidity. Even though the take-up of carbon dioxide by the ocean is impaired, higher concentrations in the atmosphere do lead to higher rates of absorption in direct chemical exchange, with the result that the oceans are becoming more acidic, turning into weak dilutions of carbonic acid. This is now building up towards levels which are lethal to marine organisms (including plankton) which are critical to the ocean’s effectiveness in mopping up carbon dioxide. For instance, among the significant organisms from this point of view are the minute sea snails—pteropods—which use large quantities of carbon to form their calcium carbonate shells. They are essential to many marine ecosystems and, when they die, the carbonate falls to the seafloor. It has been shown that, in seawater at the level of acidity expected later this century, the integrity of their shells is destroyed.^C111

• Decline in plants’ ability to absorb carbon dioxide. The effect of higher temperatures on plants has already been studied. At 2–3°C above pre-industrial levels, there are lengthening periods of the annual cycle during which vegetation becomes a source of carbon dioxide, adding to the carbon dioxide which is already in the atmosphere, rather than absorbing it as a sink.^C112

• The impact of drought on forests. There is an increasing loss of vegetation available to soak up the spare carbon. This is happening for several reasons. The tropical forests of South America are getting drier, and there are already signs of dieback. Stretches of the forest depend on each other, in the sense that much of the rain that falls on one area is promptly recycled, being taken by air currents to fall again and again on other areas of the forest further along. This means that if one area fails the rain will not be recycled, and the other areas will quickly dry out, releasing carbon dioxide in large quantities as they do so. And if the forest survives drought, it may not survive fires that follow. The fire releases most of the carbon the forest absorbed during its lifetime, together with the carbon stored in its soil.^C113

• Albedo. Snow and ice reflect back into space most of the solar energy that reaches them. As the ice retreats, the dark surfaces of the land and sea are revealed, so that most of the solar energy that reaches them is absorbed, increasing the rate of warming. This effect is well established in the models, but that has not banished surprise. For instance, the rate of melting of the Arctic sea ice is now acknowledged to be higher than the models have generally predicted. If, or when, the Arctic is ice-free, then there will be consequences for the Greenland ice sheet, as discussed in the following.^C114

• The stratosphere. The sequence is complex and it is not surprising that it has only recently been (tentatively) described:

The troposphere—the lowest layer of the atmosphere (about the first 10 kilometres)—warms up as carbon dioxide concentrations rise.
———-↓
So less heat escapes from it, and this in turn cools the next layer—the stratosphere (between 10 and 30 kilometres up).
———-↓
The cooling changes the energy distribution in the stratosphere in a way which increases wind speed, particularly that of the ‘stratospheric jet’ which circles the Arctic, especially in the winter.
———-↓
The stratospheric jet influences the speed of the warm westerlies in the troposphere, and they become faster, too.
———-↓
The westerlies drive further into the Arctic, warming it, and contributing to a further cooling of the stratosphere . . .^C115

2. Abrupt changes

The typical graph we see, illustrating the rise in temperature and carbon dioxide concentrations over the years, is smooth. But complex systems do not keep to such behaviour. They may mature smoothly and incrementally, but when they break down, they do so abruptly; breakdown tends to be untidy and messy and, as the stresses on the climate build, it becomes increasingly probable that the tension will snap. The IPCC recognises the likelihood of abrupt change affecting aspects of the system—and perhaps especially the ice sheets—and it adds, “If a large-scale abrupt climate change were to occur, its impact could be quite high.”^C116

In fact, it is only since ice cores from Greenland have been studied—with their preserved record of temperatures and conditions back through the whole of the last glaciation and into the temperate Eemian interglacial period that preceded it—that the truth about a fundamental property of the climate has dawned. The Holocene period in which we live, which started some 15,000 years ago, has been untypical in one fundamental way: it has been remarkably stable, by the standard of the climate’s previous behaviour.^C117 But turbulence is deep in the nature of Gaia, and even the Holocene has had its ups and downs . . .

• From the end of the last glaciation to about 3500 BC, the area of Northern Africa which we now know as the Sahara Desert was a lush forested region of intense sunshine, reliable rain, massive rivers and water-loving animals such as hippos and crocodiles. The precession of the Earth (the slight wobble as it spins) had helpfully positioned the region for the fullest possible intensity of the sun during the summer, causing strong convection currents of rising warm air which drew in rain. Abruptly, it came to an end: when the precession shifted, the ecosystem changed into the rainless desert which we know today.^C118

• The Mayan civilisation in the Yucatan Peninsula (Mexico) was 2,500 years old and apparently flourishing when, between the eight and tenth century (about the start of the Medieval Warm Period) it was hit by a series of droughts, by which it was completely destroyed.^C119

• The four-century-long Medieval Warm Period which began in the tenth century had vineyards growing in Derbyshire, provided the agricultural wealth which paid for the cathedrals, and lured a Norse colony to settle in Greenland.

• The Little Ice Age that followed destroyed the Norse colony and provided the intense cold represented in the European snow scenes painted by Breugel and Hendrick Averkamp. Iceland, being surrounded by ice for many miles, could not be approached by shipping. Intensely cold weather in North America brought conditions which decisively ended the earliest colonists’ attempt to live off the land on Roanoke Island in Virginia. In Italy, wood grew exceptionally slowly in the cold, providing the dense maple and spruce used by Antoni Stradivari for his violins.^C120

• The most dramatic climate shock, 13,800 years ago, was the Younger Dryas event, named after a small, but hardy, white rose that thrived in cracks in exposed rocks between the ice, in an environment that practically no other plant could stomach. This was the 1,500 year encore at the end of the last glaciation, when meltwater from the giant Lake Agassiz covering much of the American Midwest burst through the ice dam which had contained it, and flooded into the North Atlantic—the place where the warm Gulf Stream reaches the end of its world tour, sinks deep beneath the surface, and heads back south. The driver of this circulation is the interaction between the salt water and the very cold temperatures: as salt water reaches freezing point, it separates out into fresh water and very salt water. The fresh water then freezes, while the very salt water sinks towards the seafloor, and this acts as a pump which pulls the Gulf Stream’s surface water north, while pushing the cold, salt water down into the depths for the return journey. When the fresh water from Lake Agassiz flowed into the area it diluted the salt water so much that there was not enough of it to drive the pump, and the Gulf Stream stopped. Without its warming effect, Northern and Central Europe was back under ice and tundra.

With the exception of the Younger Dryas—which really belongs to the preceding glaciation more than to the Holocene—these events were comparatively minor and localised, relative to the violent changes which preceded the Holocene as far back as current ingenuity allows us to see. This earlier record is one of Dansgaard-Oeschger events—short, (century-long) periods of respite from the deep cold of the ice age—and Heinrich events—longer periods of deep cold—and the dramatic lurches into the depth of the glaciations themselves. Climate history, apart from the special case of our own benign Holocene, has been a story of abrupt fluctuations. An apt analogy is the confused behaviour of a driveway light, activated by movement: when you approach it in the twilight it doesn’t know whether it’s night (when it is meant to switch itself on) or day (when it isn’t), so it switches neurotically on and off. It has only two states: it is a binary system; it doesn’t do moderation.^C121

Except that, in the case of the climate, the two states—icy vs. temperate—that have existed for the last three million years may not apply in the future, because the planet is being presented with a new situation. The quantity of carbon dioxide in the atmosphere is outside the range of the whole of that period; and the planet has never before experienced high levels of carbon dioxide while at the same time supporting ice caps at the poles. This is disequilibrium on a new scale. It won’t stay put: disequilibria never do. In the past, the change from warmth to ice and back again has represented an oscillation “between two apparently quasi-stationary stages”. When it moves, it tends to move fast—over a period of twenty years or less. As the disequilibrium of high carbon dioxide levels coexisting with icecaps has not been known before, there is no observational basis here for scientific confidence. And yet it is certainly outside the established range of periods of sustained warmth followed by sustained periods of cold. When equilibrium has been dislodged, giving way to disequilibria, we can expect chaotic, surprising and sometimes violent interactions, over a long period. From the planet’s point of view, the new turbulence could be normal.^C122

3. Politics and practicalities

Concentrations of carbon dioxide, along with all the other gases in the atmosphere with an impact on global warming, are already in a state of “overshoot”. If we are to have any chance of maintaining the climate system in the relative stability of the Holocene period, they would need to be brought down from the roughly 390 parts per million (ppm) in 2010 to 320 ppm or less. The timescale is fuzzy, with scientific opinion ranging in emphasis: there is the view that the reduction has to be “as soon as possible” (ideally tomorrow morning)—that is, an almost immediate cessation of carbon emissions, together with extensive reforestation and an end to any further felling of forests or exploitation of peat bogs anywhere in the world, might have a chance of making useful progress in the right direction. And there is the view that it is not so much the timing that matters, as the cumulative emissions—although, of course, the downturn must be soon and steep if those cumulative emissions are to be kept within the needed limits.^C123

The best that international debate can aim for at present is stabilisation at 450 ppm. Even this would require deep cuts in emissions, starting soon. In fact, after a peaking point no later than 2015, emissions of carbon dioxide and its equivalents from all energy and industrial processes would have to fall by 4 percent each year. At the same time, emissions from deforestation would have to cease (if they didn’t, emissions from energy and industrial processes would need to fall by as much as 6.5 percent each year, as a kind of nominal compensation). Is that going to happen?^C124

If not, try something more realistic—a turning point of 2020, followed by a reduction of emissions by 3 percent each year. That would eventually lead to a notional stabilisation at 650 ppm. It is “notional” because it assumes that there are no feedbacks. At 650 ppm of CO₂ (or the equivalent, when all greenhouse gases are considered), the temperature would rise to around 4°C above pre-industrial levels. The effects of this would, in turn, carry the planet up to six degrees above pre-industrial levels, and to a level of trauma comparable to the Permian Extinction.^C125

Points of inflexion: where the curve changes direction

We do not know what is going to happen, but we do not need to be completely innocent of any suspicion about what might happen. Here are three possible sequences:

1. Methane

The very large stores of methane on the planet are maintained mainly by low temperatures, with the methane on land and at sea in the Arctic kept stable under a lid of permafrost. However, there are signs that escapes of methane from these stores have already begun, and that this is beginning to take the form of a major feedback, with decisive potential. In September 2008, researchers off the north coast of Siberia observed the sea foaming with gas bubbling up through “methane chimneys” from the seafloor; the conclusion they have drawn is that the permafrost seabed is melting. Orjan Gustafsson, one of the leaders of the expedition, comments,

Yesterday, for the first time, we documented a field where the release was so intense that the methane did not have time to dissolve into the seawater but was rising as methane bubbles to the sea surface.^C126

The climate scientist Sarah Raper points out that the interpretation of observations such as these is difficult, owing to the lack of a baseline with which to compare it:

The trouble is we don’t know if this is ‘normal’ or not—i.e., we don’t have a long historical record to look at.^C127

But we do know that, unless there are compensating feedbacks, methane releases set up classic positive feedback as the higher temperatures produced by more methane lead to the escape of yet more methane.

2. The Gulf Stream

It is possible that all the summer sea ice in the Arctic will have disappeared before the end of the decade 2011–2020. The substantially higher Arctic temperatures that will follow will speed up the melting of the Greenland ice cap, pouring vast quantities of cold fresh water into the North Atlantic. We do not how great the loss of salinity (saltiness) and change in sea temperature would have to be for the Gulf Stream to break down as it did in the Younger Dryas, nor how long it would take. But if that flow of water stopped, it could lower the temperatures of Northern Europe to the point at which its agriculture becomes impossible, at the same time as drought develops in the lower latitudes.

Conditions would be similar to those of the Younger Dryas although, in our own day, things would be complicated by the high level of greenhouse gases in the atmosphere, which would tend to make the lower latitudes considerably warmer than they were in the Younger Dryas. They might also moderate the cold in the northern latitudes, but the absence of a Gulf Stream—and less tropical forest to sustain the flows of water vapour and heat away from the lower latitudes—could create conditions for large temperature differences between the low latitudes and the poles. Storms could be expected.^C128

So, will the Gulf Stream stop? We don’t know. But try that as your report to a general, whose whole information set consists of uncertainty. Reconnaissance does not present a collection of disconnected uncertainties. It builds up a picture. And the picture is one of interlinked stabilising mechanisms across the planet being driven close to the edge.

3. Reprieve

There is, evidently, something about the Holocene era which has enabled it to maintain relative stability, in spite of a continued record of disturbances related to the sun—changes in the Earth’s orbit, its tilt precession (wobble), and variations in the amount of radiation it receives. The stability has survived despite the invention of agriculture, which itself was a substantial source of carbon dioxide and methane, and shocks such as the drying-up of the Sahara region. We are, at the time of writing, still living under the benign regime of the Holocene.

At the same time, the world’s stock of oil, gas and coal is declining (Energy Prospects), and the option of reducing consumption at a rate much faster than energy resource depletion alone would impose would open up if nation after nation were to take up the use of TEQs (Tradable Energy Quotas), within an effective global reduction framework. Even the sun seems to be lending a helping hand; at present it is getting by on reduced power, and this will be in our favour for the early decades of the century. So we may have good luck and hope on our side; we may scrape through. Not without surprises, but with the possibility of being shocked and shaken into a better frame of mind, good order and improved judgment.^C129

From the point of view of deciding what to do, it does not matter which (if any) of the above three sequences come to pass. There is only one way forward, and that is to reduce carbon emissions on a trajectory of decline much steeper than seems reasonable or comfortable, and to turn at last to the ingenuity and good faith of people to achieve unreasonable results. The point is not that we know what will await us if we don’t do these things, but that we know what resources of invention and intelligence are available to us if we do. The information technology that we carry in our heads has been underestimated of late. If this were activated, it could, just possibly, be a match for the melting Greenland ice sheet and the bubbling methane.

In the end, this is a matter of good housekeeping; a practical skill which has been devalued in a regime preoccupied with the magic of constant growth. We are looking now for something more down-to-earth and less fantastic: the individual and collective empowerment of lean thinking.

Related entries:

Climacteric, Self-Deception, Butterfly Effect, Unintended Consequences, Systems Thinking, Resilience.