Catastrophe – an event causing great and often sudden damage or suffering, a disaster. The word gets over-used, but we all know pretty much what it means. We also know that true catastrophes do happen. On Tuesday evening, 29th December, at 11:39 p.m. Earthquakes Canada recorded a magnitude 4.7 quake just east of Vancouver Island, near Sidney. It woke people up, but it was not a catastrophe. At magnitude 4.7 it caused essentially no damage and no real suffering; it was just a reminder that earthquakes do happen from time to time, and can be a lot more serious than this one. I remember experiencing a similar-sized quake in Sydney, Australia many years ago. It woke me, I wondered briefly what had happened and promptly went back to sleep. Only that morning did I learn on the news that it was the largest quake to have hit Sydney in many years! Vancouver (and Sidney) sit in a seismically much more active region than Sydney, and Tuesday’s quake is a reminder that the really big one will come eventually. Tectonic plates do not slide over each other without causing a certain amount of calamity from time to time.
Earthquakes can be catastrophic. So can volcanic eruptions, massive floods, ferocious forest fires, and the impacts of sizeable meteorites, and those are just the main types of natural causes of catastrophe. Frightened or rampaging mobs, structural failure of major buildings or other infrastructure, and mid-air failure of an aircraft can also have catastrophic results although usually on smaller scales. But why do we need to talk about catastrophes?
We need to talk about catastrophes because otherwise our feeble minds forget that they can and do occur. I’m told the most frightening thing about experiencing an earthquake of any size much above magnitude 4 is that you become instantly aware that the environment in which you spend your days is impermanent. When the ground itself is bouncing about, that is foundationally unnerving because we all construct a reality that begins with the assumption that gravity works, that down is down, and that the ground stays still. (That is also one of the reasons why we used to think the Earth was flat.) Earthquakes remind us that we are frail sentient beings clinging more or less tenuously to a rocky sphere with its own internal tensions – hence the earthquakes — hurtling along a path through the cosmos at a speed and direction totally beyond our control. This is an ego-deflating reminder for all except the Donald Trumps of the world, and a reminder we probably need to receive from time to time.
Sir Charles Lyell, viewed by many as the ‘father’ of modern geology, was born in Kinnordy, Scotland in 1797, although by the age of two he was living near Southampton and the New Forest in the south of England. A son of wealth, he was able to spend his life dabbling in natural history, but he earned a B.A. from Oxford in 1819, and went on to study law before ending up practicing geology. Coupling his inquisitive mind with attention to detail during a long series of field excursions throughout Europe, plus several trips to North America, he radically altered thinking in his field. Contrary to the prevailing fashion, he sought to explain geological features through the prolonged action of processes such as erosion by wind or water that we can see today, rather than through the agency of supernatural forces – giant (biblical) floods, paroxysms of mountain building, or disappearances of land bridges beneath the waves. This led to an affinity for evolutionary ideas, and the conclusion that the Earth was immensely old. His monumental, 3-volume treatise, Principles of Geology, was a landmark that set the basis for a whole new way of looking at geological forms and the processes that built them. His approach came to be called uniformitarianism because of its stress on the actions of small forces causing slight changes that accumulate over long periods of time. Charles Darwin, an early fan, applied Lyell’s thinking to the radiation of animal species set out in the fossil record, and developed his idea of ‘descent with modification’ the cornerstone of his theory of biotic evolution.
Uniformitarianism fits with the idea that the planet does not do unusual things. It makes sense to us, because it has been around almost 200 years. But as with all good ideas, it can be taken too far. We need to remember that, occasionally, the Earth does do unusual things, unusual things that can lead to catastrophic outcomes.
Reading the many words being written about climate change, it is common to come across the phrase, tipping point. A tipping point occurs when the planetary system enters a state where an unusual event, usually with catastrophic consequences, is very likely to occur. Tipping points are sort of the mirror image of equilibria. When the planetary system is in an equilibrium state, steady-as-you-go is the rule and there may be very little change in conditions, and certainly no catastrophes. The reason the writing on climate change is so full of tipping points is because scientists recognize that while equilibrium and uniformitarianism are the rule, sometimes the planet does do unexpected and unusual things.
The Intergovernmental Panel on Climate Change or IPCC is that UN invention that seeks to produce a consensus view on the science of climate change every 5 years or so. To do so, IPCC engaged the participation of very large numbers of climate and other environmental scientists in a rigorous process of evaluation of published, peer-reviewed science, to prepare detailed reports on the state of the science and the likely future climates under specific assumptions regarding our economic activity and energy use. IPCC has come in for way more than its share of criticism from various sources, particularly in the denialist community, but it has also been criticized by scientists who accept that climate is indeed changing because of human activities. One of the more interesting criticisms of the IPCC process is that the way in which the IPCC process works eliminates any suggestions that dangerous tipping points may be on the horizon. By seeking a broad consensus, the IPCC process eliminates rational scientific conjecture, the tiny eureka moments that occur when a scientist has a brilliant insight, the creative sparks that make science live. And tipping points are, by nature, subjects of conjecture until after they are passed.
To think a bit about tipping points and catastrophes, let’s first think about equilibria and uniformitarianism. The simplest definition of an equilibrium state is that it is a state in which a complex system (the planet) is likely to remain, because forces acting to keep it there are stronger than forces causing it to move away. The usual metaphor is a frictionless pool table that has one or more flaws, low patches in its surface.
A billiard ball placed on this surface and given a push will bounce around for a bit, but will almost invariably end up stationary in one of the depressions. We can also imagine a pool table, still frictionless, that is perfectly flat, and a set of tables with more or less deep depressions in the surface. The ball set in motion on the flat table will bounce around indefinitely, and will be no more likely to be located at one point on the table than at another. The balls set in motion on the dimpled tables will tend to occur more often than you’d expect at the low points, and will come to rest in one of them, but this process of coming to rest will happen more quickly in the more deeply contoured tables. On a really strongly deformed table, it will take a significant push to get a ball at rest in a depression out of that low point and moving over the table. We, and the rest of the biosphere, live on a non-level pool table, and environmental scientists argue about the depth of the depressions, the metaphorical analog for the strength of the forces keeping the system at the equilibrium points. Some of us think that the world exists in a universe of only weak forces acting to maintain equilibria, while others believe those forces are quite strong. The concept of the balance of nature, a concept which I believe is overstated and wildly improbable, describes a universe of strongly maintained equilibria. And the tipping points? Those are the places on the table from which the ball is very likely to move quickly towards a nearby equilibrium state, the high points on this very imperfect pool table.
How glaciers melt
If frictionless, warped pool tables are not your thing, let’s turn to some real equilibria in nature. One of the best climate-related examples concerns the status of a glacier. A continental ice sheet begins to grow when the snow that falls during a winter does not all melt away during the coming summer. Over a succession of such years, the residual snow layers accumulate one on top of another and get compressed to form ice. Obviously, ice formation is critically dependent on snowfall and temperature.
A glacier is an equilibrium tied up with some impressive time lags. Snowfall on top is balanced by melt on the surface and at the front. The glacier grows or shrinks to keep these in balance.
As the ice pack builds up, it begins to spread laterally under its own weight, and since conditions forming ice are likely to exist at higher elevations, this lateral spread usually moves the ice towards lower elevations. This mass of ice will grow year by year, and spread even further, until its outer, lower edges are in places where the temperature encourages melting. When the rate of melting exactly matches the rate of spreading of the ice layer, growth of the ice sheet ceases. Snow continues to be added to the higher elevation portions, ice continues to flow out to lower elevations, and melting from the surface and at the outer edge removes ice at a rate matching the rate of flow. Such glaciers exist on mountain ranges at all latitudes and across Greenland and Antarctica, as apparently permanent features of the landscape. Yet they are simply an enormous equilibrium with ice being added on high, and removed down below. Change the temperature, or change the rate of snowfall, and the glacier responds by ‘growing’ or by ‘shrinking’ as the case may be. At the present time, virtually all glaciers on the planet are shrinking or receding as their equilibria get reset.
What I have just described is a uniformitarian description of how glaciers exist and how they behave. It is generally, over the long run, correct. There are enormous time lags in this particular system, such that once snowfall increases, or once temperatures cool, the process of growth to establish the new equilibrium state will take many years. And once temperatures warm, or precipitation decreases, it will take a similarly long time for the new smaller glacier to result. At present, most glaciers on the planet are getting smaller year by year as they race slowly to the new equilibria caused by warmed temperature. The uniformitarian view may include time lags, as well as processes that take eons to have any measurable effect on the environment – imagine wind sculpting sandstone cliffs into their smooth, aerodynamic shapes.
Glaciers do not always behave themselves
Glaciologists have learned in recent years that when glaciers melt extensively (as they have been doing in recent decades), that melting does not just take place on the surface and at the front edge. Some of the melt-water that pools on the surface finds its way down cracks and crevices into the interior to the glacier, enlarging these cracks and crevices as it goes. Water pools deep within and at the base of the glacier providing a lubricating layer between the ice and the underlying rock. Similarly, where glaciers extend far enough to reach the ocean, as they do in parts of Greenland and Antarctica, the melting at the front of the glacier is enhanced by wave action and by tides that stress the (floating) front of the glacier. These effects, plus all the melting lead to sudden ruptures in the ice as icebergs are calved. Putting the sudden production of new icebergs together with the tunneling out that goes on due to melt water moving about within the glacier and suddenly that uniformitarian vision of the glacier at equilibrium becomes a whole lot more chaotic. The possibility of a well-lubricated glacier ‘suddenly’ sliding downhill, perhaps into the ocean, is very real. Sudden enough and big enough and that event would produce a tsunami of impressive proportions as well as a ‘jump’ in sea level. A little bit of slippage will likely not be noticed, but if one of Greenland’s or Antarctica’s larger glaciers ‘suddenly’ gave way, it would be a catastrophe of global consequence. That is one scenario discussed by James Hansen in his book, Storms of My Grandchildren. More recently, Hansen has been more concerned by another aspect of glacial melting – the fact that scientists are only now beginning to understand how glaciers melt when conditions are becoming rapidly warmer.
This is the underside of a glacier in a Swiss lake, showing the extent to which it is dissolved by the surrounding water. Photo © Franco Banfi
While it is possible to see the melt-water carving out great under-ice river systems, we do not yet know how rapidly these form, how extensive they become and what the links are between pattern of warming and pattern of melting. And there are other issues for glaciers that extend into a lake or the ocean as they do in Greenland and Antarctica. In a controversial article made public last July – controversial simply because Hansen chose to make it public in advance of peer-review, by using a process set up ironically to make the peer-review process itself more public and egalitarian – Hansen and co-authors report on the extent of sea level rise during interglacial periods within the Pleistocene when temperature was similar to today and CO2 concentrations were lower. The article is expected to eventually be published in the journal, Atmospheric Chemistry and Physics, and is currently available on that journal’s ‘discussion’ website where anyone can comment, hopefully constructively, and participate in the peer-review process.
What does the Eemian have to do with today?
Hansen et al examine the last interglacial period before the end of the Pleistocene. Termed the Eemian, it ended with a rapid return to glacial conditions about 118,000 years before the present (-118kA). Evidence suggests the Eemian climate was at most 2oC warmer than preindustrial times (about 1Co warmer than now), and most likely was only a fraction of a degree warmer than now. Yet sea levels by the end of the Eemian were 6 to 9 m above today’s level. This implies very considerable melting of glaciers during the Eemian. By contrast, IPCC is currently projecting a sea level rise of less than 1 meter by 2100 under business-as-usual (RCP8.5) conditions.
Hansen et al. reason that if glaciers melted extensively during Eemian times, as the high sea levels suggest, there is no reason why they should not melt extensively under the conditions we are now imposing on the planet. It is already known that glaciers that extend into the ocean experience more rapid melting at the front than they would otherwise because in cold climates the ocean is warmer than the air. This causes an under-cutting of the advancing front. Given that many such glaciers are grounded on rocky shelves some distance out from what would be the shore, and well below sea level, there is potentially considerable ice surface available to be acted on by warm sea water, and the real possibility that the under-cutting will ‘remove the brake’ on outward movement being caused by the shelf on which the glacier is grounded. To complicate things still further, the release of the melt-water adds a lens of essentially fresh, lower-density water on the immediate sea surface, stabilizing the water column and reducing the tendency for deeper water to rise to the surface releasing heat to the atmosphere (that rise is a part of the Ocean Conveyor global ocean circulation). Instead that heat is trapped in the upper water column and available for melting of the underside of the glacier. There is some growth of sea ice, but the rate of glacier melting increases. And, yes, there is already evidence that glaciers in Greenland and Antarctica are melting at rapidly increasing rates (doubling time around 10 years).
The effects of the melt-water in stabilizing the water column and trapping heat near, but not at, the surface, also include a general slowing of the ocean conveyor (of which that southern ocean rise by deep water is just one part). As a consequence there is a reduced flux of heat from tropics to poles, a stronger latitudinal gradient in temperature and stormier weather.
Hansen and colleagues also discuss evidence for strong storms during the Eemian. Studies on the Bahama platform have revealed the presence of Eemian age sand ridges, several kilometers long and apparently built by long-period waves from the northeast. These ridges were formed near the end of a period of high sea level, otherwise they would have been eroded by subsequent events. Evidence that the ridges were built rapidly comes in the form of trees buried in living position within them. Other ridges, resembling wave run-up formations, occurring at heights up to 40 m above present sea level, and high above the nominally 6-9 m higher Eemian sea level, also reveal the magnitude of storm surges. Finally, on North Eluthera, Bahamas, there are enormous, 2000 tonne boulders that have been tossed up beyond these ridges by storms.
Independent studies in Bermuda reveal Eemian-age sand ridges of similar form along the northern shore of the islands – a shore that is well-protected by an extensive, reef-supporting shelf. Hansen’s conclusion is that not only was sea level 6-9 m higher than at present, but tropical storms were substantially more severe – exactly what might be expected if the overall global ocean circulation had been slowed.
Would a re-play of the Eemian, or something similar, in coming years constitute a catastrophe? In Hansen’s view it surely would, at least for the billion people living near sea level. In his words:
“We conclude that multi-meter sea level rise would become practically unavoidable. Social disruption and economic consequences of such large sea level rise could be devastating. It is not difficult to imagine that conflicts arising from forced migrations and economic collapse might make the planet ungovernable, threatening the fabric of civilization.
“This image of our planet with accelerating meltwater includes growing climate chaos and storminess, as meltwater causes cooling around Antarctica and in the North Atlantic while the tropics and subtropics continue to warm. Rising seas and more powerful storms together are especially threatening, providing strong incentive to phase down CO2 emissions rapidly.”
I cannot help but conclude by referring to the social chaos caused by a few million displaced Syrian refugees, and the somewhat greater chaos if a billion or so were displaced by rising seas. Walls along national borders, and careful control of who is permitted entry, suffice only in a cartoon world.
Some other catastrophes waiting in the wings
The melting of glaciers is not the only aspect of climate change that might bring us surprises in coming years. One of our problems is that we are increasing the concentration of CO2 in the atmosphere very rapidly compared to at any prior time in Earth’s history, and we have been, until very recently, increasing the rate at which we change it. (If 2015 additions do turn out to be no more than those in 2014, it will be a sign that the upward spiral may have been slowed. We need to see stable or falling emissions over several years while the economy grows to be sure.) Complex systems often have the characteristic that they respond linearly to perturbation when the disturbance is slight, but show unexpected, chaotic, or catastrophic behavior when the disturbance is stronger.
Some of the other possible catastrophes? Here are three ways things could go seriously off the rails. They concern melting muskeg, over-committed oceans, and fried forests. First the melting muskeg.
Canada’s north contains 5400 km of ice roads. These are not short bush roads 15 or 20 m wide, but major roads stretching hundreds of kilometers and traveled by giant transports trucking in goods and trucking out products. They are lifelines built by pumping water onto the road bed built over the permafrost to freeze and create a solid pavement. They used to be usable for 3-4 months a year, but each year the usable season seems to get shorter. Across vast areas of North America and Asia there exists permanently frozen tundra. Typically, the frozen soils impede water flow and the surface is low, marshy, with low shrubs and extensive bogs or muskeg. Everything is frozen solid all winter; the upper layers thaw during the warmer season and any road becomes impassable. Buried in the frozen soils are enormous quantities of organic matter, protected from decomposition. Now, with climate change, not only must northern countries face the difficult task of providing roads across this marshy landscape, but we must all cope with the emissions of methane that result as the thaw progresses. It is estimated that the Arctic permafrost contains 1.7 trillion tonnes of carbon, about twice as much as is currently in the atmosphere. Most of that carbon is in the form of methane, and thawing of even an upper layer of the permafrost releases some of this methane to the atmosphere where it adds to the greenhouse effect in a vicious positive feedback causing more warming and more methane releases. (There are also substantial methane stores in subtidal Arctic sediments that could be released if water warms sufficiently.)
Slumping of thawed permafrost adjacent to the Alaska Highway, Yukon, Canada. Image © Guy Doré/Laval University.
One of the features of melting permafrost is sudden slumping of patches of ground. These slumps can damage buildings and other infrastructure, and ruin roads. But the methane releases could greatly accelerate climate change and we have no idea how warm the planet would become before the process stops. (A ‘sudden’ burp of methane from marine clathrate stores is believed to have triggered the Paleocene-Eocene Thermal Maximum some 55 million years ago – a sudden warming to the warmest phase of the entire Cenozoic.) The nastiest part of this methane catastrophe is that if we do not reduce CO2 emissions fast enough we could move the Arctic ever closer to wherever the tipping point lies for run-away permafrost melting. And once that point is reached we would be incapable of bringing the warming process under control.
If the muskeg problem seems a little too real, this one may seem a little less likely. At the present time, around 30% of our CO2 emissions dissolve from the atmosphere into the oceans. There it dissociates to form carbonate, and causes the problem of ocean acidification. However, the solubility of CO2 in water is temperature dependent, and as the oceans warm the partitioning of CO2 with the atmosphere is going to shift. More of our emissions are going to remain in the atmosphere to contribute to warming of the environment. This likely would not happen suddenly; instead, year by year a smaller and smaller fraction of CO2 would move to the oceans and rate of climate warming would speed up. The effect would be to throw a spanner into any plan we might have dreamed up to emit as much CO2 as we could get away with without having the climate warm beyond 2oC. We’d have to suddenly reduce emissions, or face more warming that was wanted. This should be viewed as a sociological or political calamity rather than an existential catastrophe.
The world’s forests are the other major sink for CO2 emissions, removing somewhere around 20% of our emissions from the atmosphere and storing the carbon in the timber and in the soils. Northern (boreal) forests and tropical forests are currently almost equivalent in the amount of carbon removed from the atmosphere each year: globally, northern forests are estimated to sequester 43%, while tropical forests sequester 41% of all carbon sequestered on the land. Among the most important forests are Canada’s boreal forest, the largest contiguous forest on the planet, and the Amazon rainforest of South America, the most biodiverse region on the planet. Some environmental scientists fear that both these forests could be under increasing threat from forest fire, and that a drying Amazon basin that is predicted in the climate models could lead to a forest-free Amazon by late this century. The growing concentration of CO2 in the atmosphere stimulates plant growth and therefore should be enhancing the extent to which forests sequester carbon. The tropical forests have been increasing their primary production as expected until now, but the boreal forests have not. Apparently increased dryness and heat have harmed these northern trees and despite the enhanced CO2 they are growing more slowly. Part of the ‘slower growth’ is readily apparent in the increasing incidence of fire during the hot dry summers.
In the eastern Amazon, rainfall has been declining, and fire incidence has been increasing. That part of the Amazon is already beginning to change and the rest could follow. If drought becomes sufficiently extensive, it is possible that fires could grow in size and substantially alter this immense tropical forest. Regardless of whether it’s the rainforest or the boreal forest, a burning forest not only ceases sequestering carbon, it delivers much of its enormous store of carbon straight back to the atmosphere, further changing the climate. Indeed, some fear that the growing extent of fire in tropical forests – much of it deliberately caused to clear land for palm plantations and other uses – coupled with the growing incidence of fire in boreal forests — is going to lead in just a few years to the elimination of the land sink for carbon, and releases of enormous quantities of carbon to the atmosphere. Slowly, or quickly? Probably quite quickly once the trend starts, and it may have started already. Another catastrophe to deal with.
And just one more thing…
Finally, just to make sure every reader comes away a tiny bit uncomfortable, there is one more point to add. The possible speed-up in the melting of glaciers and the resultant ocean impacts, the releases of methane from thawing muskeg, the collapse of the ocean’s capacity to absorb CO2, and the failure of our forests to continue to sequester carbon could all happen together. I think they call that an absolutely perfect storm. These tipping points probably won’t coincide, but they could.
Many denialists criticize those who advocate for action to slow down climate change. The denialists laughingly denigrate the whole concept of the precautionary principle (which simply states that in a situation of uncertainty it is wise to proceed slowly and cautiously), on the grounds that this is just one more device to disrupt our economic system. I can think of no action by us that would be more likely to disrupt our economy, and a good deal more, than to soldier on, business as usual, ignoring the facts of climate change, confident that, in the end all will be well. Only the fool moves blithely forward assuming all will be well until the day the catastrophe arrives. We do not need to huddle trembling under the bedclothes waiting for the climate catastrophe to come, but it does not hurt to appreciate the dangers that may be lurking. And to get on board with the need to cut CO2 emissions now.