Category Archives: Climate Change; a Geo Perspective

Volcanism does not cause glaciations; let’s turn this statement on its head

It is almost a truism that volcanic eruptions influence climate. Cold winters and even failed crops, particularly in the northern hemisphere, followed on the heels the Tambora, Krakatoa, and Pinatubo eruptions.  But these climate aberrations were relatively short-lived, counted in years; the stratospheric aerosols and fine volcanic ash that reflect solar radiation back into space, eventually succumb to gravity and fall to earth.  Eruptions of this kind do not result in long-lived, or permanent changes; they are temporary blips on an evolving earth and an evolving climate.

There have been stupendous volcanic outbursts in the more distant geological past, that have wreaked havoc on the global climate and threatened life itself. One such event was the eruption of the Siberian Traps, 250 million years ago, an outpouring of lava, volcanic ash, and gas that lasted almost one million years.  Individual lava flows, in a single outpouring, produced upwards of 1500-2000 cubic kilometres of basalt.  The cumulative volume of lava and ash would have been sufficient to cover all western Europe or USA in a layer more than a kilometre thick. The Siberian event is strongly implicated as the cause of mass extinctions at the end of the Permian Period, commonly referred to as The Great Dying; it was an event of truly global proportions. Events like this are orders of magnitude greater than the kinds of volcanic activity recorded over the last few thousand years.

So, my cliched introduction is true – to an extent. But how about turning this statement on its head; the excesses of a changing climate can influence volcanism. The possible links between global climate change, volcanism, and the carbon cycle have been argued for decades. First, we need to establish some time scales. Events like a Krakatoa-induced cooling persist for only a few years – usually less than 10. Contrast this with the time frame of your average glaciation, and we are now dealing with (roughly) 100,000 years. How do signals of volcanism compare with these longer-term cooling and warming episodes (glaciations and interglacials)? It turns out that there is a relationship between volcanic activity and glaciations. But it is also apparent that volcanism lags the onset of climate change that herald glaciations or interglacials, in some cases by several thousand years. Therefore, volcanism cannot be a primary cause of such climate changes, at least on a time scale of 1000s to 10,000s of years (a suggestion made almost 4 decades ago by Rampino, Self, and Fairbridge in their paper Can Rapid Climate Change Cause Volcanic Eruptions? published in Science, volume 206, 1979).  These authors hypothesis that the temporal association between volcanism and major climate change is caused not by the eruptions themselves, but changes in water-ice budgets and stress associated with the subsequent loading and unloading of the earth’s crust. The hypothesis is appealing, but until recently it has lacked any reasonable kind of testing and verification.

As happens so often in science, research in one direction can lead to unexpected results that point investigations to new and exciting directions. One such project along the subducting coast of South America, undertaken by S. Kutterolf and colleagues at GEOMAR (Helmholtz Centre for Ocean Research Kiel) provides good evidence for links between glacial cycles and volcanism.  The Initial data base consists of volcanic ash layers retrieved from cores into the sea floor off South and Central America.  The more than 80 ash layers identified provide a history of major, landward eruptions up to one million years ago.  This data set was augmented by volcanic ash – tephra records from various ocean drilling projects at several sites around the Pacific Ring of Fire (more than 400 ash layers were eventually identified). Once the age of all the ash layers had been established, the frequency of eruptions was analysed and plotted. What surprised the researchers, was the prominence of volcanic activity close to, but consistently lagging by about 1-5 thousand years, an important astronomical cycle – the Milankovitch Obliquity Cycle.  Obliquity records the gradual shift in the earth’s axis from a tilt of 21.5o to 24.5o, a change that takes 41,000 years.  Shifts in the tilt axis ‘force’ an increase or decrease in solar radiation, particularly at the poles.

The Kutterolf et al. analysis makes an explicit connection between peak volcanism and the Milankovitch obliquity cycle.  Note however, that it is not changing obliquity itself that causes the increase in volcanism, but the changing climate. For example, during deglaciation ice-sheet mass decreases as melting progresses; this means that the load on the earth’s crust will also decrease.  The opposite affect takes place in the oceans where the water load increases.  Load distributions are reversed during the subsequent glaciation. The crust needs to maintain equilibrium by balancing the changing masses, such that the land surface beneath the ice-sheet rises, and the ocean basins deepen.  This balancing act is called Isostasy.

However, the balancing of loads on the crust also results in changing patterns of stress. If stress levels decrease in regions of active volcanism, like the Ring of Fire, it may be easier for magmas to ascend through the crust, promoting increased volcanic activity.  As a final piece to their argument, the authors create a model of changing crustal stress at a site along the west coast of central America; the model calculates stress for the last 120,000 years, a period that includes the last glaciation and the interglacial that we now find ourselves in.  They also plot actual eruptions along the same time-line. There is a striking increase in actual volcanic activity and modelled stress beginning about 20,000 to 22,000 years ago – a time that corresponds to the maximum extent of glaciation. Melting began soon after (significantly in the Laurentide Ice-sheet that covered a large swath of North America), with subsequent redistribution of ice-water loads and patterns of stress.

There is an interesting corollary to the Milankovitch-volcanism hypothesis. Milankovitch cyclicity predicts that we are now in a cooling phase, which means that stress levels will increase on land as ice accumulates; there should in this case be a decrease in volcanic activity. But if surface temperatures continue to increase…?  The Milankovitch time-frame is in 1000s of years, which gives us a bit of time to work on it.



A burp and a hiccup; the volcanic contribution of carbon dioxide to the atmosphere

Of the two certainties in life, volcanoes offer the most excitement (death and taxes are basically the same thing).  They are magnificent while asleep; a primeval ruggedness that stirs the imagination. We paint them, we eulogise them. And when they awaken, we run for cover. Whether in a state of dormancy or high agitation, they leave an impression on our inner and outer landscapes.

All active volcanoes emit gas; pre-, during and post-eruption. On average, 96% of volcanic gases are water vapour, the remaining components being CO2, SO2 (most common), plus a little helium, nitrogen, carbon monoxide, hydrogen sulphide, and a few halides. Volcano-derived carbon dioxide is frequently cited as a culprit for increasing atmospheric CO2 concentrations in climate change debates.  However, it is sulphur dioxide, not carbon dioxide that does most of the short-term damage to climate. Continue reading


Contrails, analogues, and visualizing groundwater flow

Analogues and analogies.  Standard dictionaries define these as a comparison, correspondence, or similarity between one thing and another, that can apply to concepts, ideas or physical entities. They are tools, used to illustrate concepts, particularly abstract ideas, to help explain phenomena or theories. Science makes frequent use of analogies. It does so because many phenomena that it attempts to investigate and explain, extend beyond normal human experience, beyond what is visible to the unaided eye, beyond what we can touch.  Well-chosen analogies can help us understand the universe without, and the universe within. Continue reading


A misspent youth serves to illustrate groundwater flow

Groundwater is always on the move. Under some conditions, in fractures or other large conduits, it can move quickly; almost at a walking pace. Under other conditions it moves inexorably slowly, like fractions of a millimeter a year. Regardless, it is always compelled to move. Movement requires energy.  Where does this energy come from?  What drives the flow of groundwater?  Answers to these questions provide the foundations to the science of hydrogeology. Continue reading


Peer review, scientific integrity and community; a comment

A rite of passage for many scientists is their elevation to some kind of editorial board, usually associated with a scientific journal.  This is where they get to review the work of other scientists and become part of the decision-making process that results in publication – or rejection.  It is an excellent means of extending one’s network of people who are interested in the same discipline.  It is always a learning experience, no matter how many papers one reviews or edits over a lifetime; new ideas, new data, new methods, new ways of expression.  Admittedly, the task of reviewing a paper can arrive on your desk at precisely the wrong time.  But a good reviewer will understand that there is always a quid pro quo; your own paper under review may arrive on someone’s desk at a time most inconvenient for them.  So you do the job anyway. Continue reading


The (not so) Great Dying; Permian extinctions

It seems that global catastrophes and the ensuing mass extinction of all manner of life-forms, asteroid impacts and Dinosaurs immediately come to mind, were made for Popular Science.  Even Hollywood is in on the act.  Perhaps it’s because, in the telling, they appeal to some innate sense of nihilism, a bit like the existential threats that politicians trot out from time to time.

A recent scientific paper by Steven Stanley published by the US National Academy of Sciences, provides some good news on this score; past estimates of life forms snuffed out by such global events, have been exaggerated.  Stanley’s reassessment accounts for the fact that extinctions are taking place all the time, in the background, and that these individual, long-term biotic events need to be subtracted from the total species loss resulting from some catastrophe.  For example, in the normal course of evolution, species are continually evolving and in doing so may create environmental pressures within their niche wherein other species are unable to compete; they may be eaten, or their food source disappears.   They gradually die off.  We certainly know this to be the case in our modern world, where human-caused extinctions are legion.  A case in point is the extinction event at the end of the Permian period (299-252 million years ago), morbidly referred to as the Great Dying.  Up to 96% of species were deemed to have disappeared, which also means that there were not a lot left to carry on the evolutionary journey towards the modern world.  Stanley’s estimates, taking background extinctions into account, now put this at 81% – still catastrophic, but not as bad as we once thought.


The (not so) Great Dying

Geological Periods are intervals of time past, for which we now have a record measured in rocks.  The beginning or end of a period is commonly defined by abrupt changes in fossils – we don’t need to know what caused these abrupt changes in life forms, only that such changes occurred.  Two well-known examples are the Cambrian (beginning 542 million years ago) where complex, multicellular animals with preservable hard parts (skeletons, shells) first appear. The end of the Cretaceous Period marks the demise of dinosaurs, although it seems the dinos were already in decline – the asteroid impact merely hastened their demise.

The Permian is also marked by a huge, and apparently abrupt loss of species, some groups lost forever.  The Great Dying was probably one of the most catastrophic extinction events ever recorded, greater even than the aftermath of the asteroid that plummeted to earth 65 million years ago.  Rugose corals disappeared altogether (image of some examples at the top of the page); 50-60% of plankton, and 60% of bivalve species became extinct.  Clearly some species survived and continued to evolve, otherwise we would not today enjoy bouillabaisse or clam chowder.


Suffocation or acid indigestion?

Illuminating the possible causes for this event has produced some interesting, even creative explanations; asteroid impact, widespread volcanism, acid rain and acidic oceans, air and sea temperature increases, algal blooms, plate tectonic assembly of a supercontinent, climate change, and even a supernova.  In many respects all (except the supernova) may be related.  Back in the Permian, the distribution of continents and oceans looked nothing like it does today.  By about 300-270 million years ago, two very large continental blocks, Gondwana and Laurasia, had combined to form the supercontinent Pangea (or Pangaea).  Pangea was surrounded by the global ocean Panthalasa.  The supercontinent began to break apart about 200 million years ago (here is a USGS animation of this process).


The end of the Permian is marked by another remarkable event.  Humungous volumes of basalt were erupted over (what is now) the Siberian Platform – the Siberian Traps.  At least 3 million km3 of lava were erupted. Putting this number in context, Mt St Helens produced about 1 km3 of lava during the 1980 eruption; the entire island of Kilauea (Hawaii) is about 25,000-30,000 km3.  The Siberian eruptions lasted about 800,000 years.  One of the by-products of volcanic eruptions is the release of gases, mostly water vapour, but also carbon dioxide (CO2) and sulphur dioxide (SO2).  The volume of CO2 released to the atmosphere over such an extended period of time must have been huge.  Both the eruptions and evolution of CO2 are currently regarded as a likely cause of the mass extinction.

Addition of so much CO2 into the air has a number of consequences.  Many species of land-based plants don’t do so well , especially in more acidic rain. Carbon dioxide also dissolves easily and rapidly in sea water, and at some point in this process, the buffering capacity of sea water (namely its ability to prevent runaway changes in acidity or alkalinity) is over come and the pH decreases (acidity increases) to the point where many animals and plants find it difficult to eke out a living.

However, certain algae can thrive in such conditions; algal blooms tend to remove oxygen from water, exacerbating already intolerable living conditions for most other species.  One hypothesis, proposed in 2013, involves microbes that metabolize carbon in the oceans, turning it into methane; the authors in this paper argue that it was bursts of methane, not CO2, that created greenhouse gas conditions and effectively poisoned the atmosphere.


Is there a disconnect between the timing of extinction and these hypotheses?

Precise dating of zircon crystals in beds of sedimentary rock that straddle the extinction event, indicate that it may have taken place extremely rapidly; no more than 60,000 years that, in geological terms, is really fast. The results of this study by Seth Burgess and colleagues were published in 2014 (Open Access).  There is also evidence, cited in this paper, that changes to the carbon cycle were already underway when the extinction began, including possible ocean acidification and increased temperatures.  However, the Siberian Trap eruptions lasted some 800,000 years.  Were the basalt eruptions solely responsible for the extinction; was there a particularly vigorous period of eruption within the 800,000 years that helped trigger the mass die-off?  Another proposal, that an asteroid impact may also have played a role, has not been entirely put to bed.  The authors of a 2001 publication claim to have detected extraterrestrial helium and argon (i.e. the kind found in meteorites) in carbon crystals (fullerenes).  However, there appears to be some dispute over this discovery, and the existence of such an impact is still poorly verified.



The terminal Permian extinction continues to hold fascination for scientists of all stripes.  This fascination extends beyond the event itself; clearly there was recovery of biota.  Perhaps this attests to the power of evolutionary processes, when in a single event more than 80% of species are eradicated, but we end up with the remarkable diversity of life in our modern world (interrupted by at least one more bolide).  Best we look after it all.


The Greenhouse Advantage

Venus and Mars.  Popular mythologies aside, neither planet has a particularly hospitable temperament.  Both are rocky planets, like earth, and both have atmospheres of carbon dioxide (about 95%) and nitrogen (about 3%).  Surface temperatures on Venus hover around 450oC; those on Mars about -53oC.  Venus is not only a tad warm, its surface atmospheric pressure is 92 times that on earth; that on Mars about 6 one thousandths of earths comfort zone.  Venus’ inclemency is the result of run-away Greenhouse processes; Mars’ is due to virtually no Greenhouse effects. Earth resides in that ‘Goldilocks zone’, being neither too hot nor too cold. Lucky us!


An energy budget

The sun heats the earth’s surface, atmosphere and oceans; earth’s internal heat contributes very little to this process.  For the climate to be stable over a reasonable length of time (decades, centuries) there must be a balance between incoming heat from the sun and outgoing heat lost to space; this heat is lost via reflection, convection and conduction.  Perturbations in this balance result in the surface either heating up or cooling down. We know that these long-term imbalances do occur because there have been glaciations and intervening periods of more clement surface conditions. Major climatic variations like these are mainly the result of (predictable) periodic perturbations in earth’s orbit and rotation, namely the Milankovitch cycles.

The total energy that earth receives from the sun is called the total radiance.  It is primarily in the form of visible and infrared light, with lesser proportions of short wave-length UV, gamma and x-ray frequencies, and longer wavelength frequencies like microwaves.  Partitioning of the incoming light is illustrated in the cartoon below. About 30% is reflected directly back to space by clouds, aerosols and the earth’s surface, especially ice sheets (referred to as the albedo); 70% is absorbed by the atmosphere, and both the solid and liquid earth.


However, to maintain an energy balance, some of this absorbed light energy must be converted and re-radiated back to space.  We witness this re-radiation in our everyday lives.  The many hues of red, blue, green, and yellow in my backyard are visible because a part of the light spectrum is reflected. If the entire spectrum is reflected, we see white; the red flowers are reflecting only light in the red part of the spectrum – the remaining light energy is absorbed. The absorbed energy is absolutely necessary for biological growth.  If no light or heat energy is reflected, we see nothing – black.





The greenhouse blanket

The Martian surface is frigid because most of the light-heat energy that gets to the planet’s surface is reflected and re-radiated back to space – Mars has no blanket.  Our own atmosphere is made up of 78% nitrogen, 21% oxygen, and very small amounts of carbon dioxide, methane, and water vapour.  Nitrogen and oxygen are almost completely transparent to sunlight in the visible and infrared part of the spectrum – they do little to help warm or cool the planet.  That task has been appointed to the greenhouse gasses; water vapour (most abundant), carbon dioxide, methane, nitrous oxide, and more recently certain industrial hydrocarbons that have chlorine and fluorine in their molecular structure.  Despite their very low concentrations in the atmosphere (water vapour is most abundant, CO2 is 0.04%, methane is even less), they are solely responsible for maintaining the kind of climatic conditions we have become accustomed to.  All except the chlorofluorocarbons occur naturally.

How does this greenhouse process work?  As an example, a carbon dioxide molecule consists of a carbon atom bonded to two oxygen atoms.  Bonding is loose enough such that infrared light energy will cause the atomic bonds to vibrate; in doing so the molecule absorbs heat.  All the greenhouse gasses operate on the same principle.  However, they also react to heat energy at different frequencies in the infrared part of the spectrum – this is illustrated below, comparing water and CO2.  Water vapour absorbs energy over certain frequencies across the light spectrum, but importantly there is a ‘window’ between about 8-15 micrometres (part of the infrared frequency range) where it does not absorb heat; heat can escape through this frequency window.

This creates for us a wonderfully fortuitous balance between some infrared heat being absorbed by water vapour and other parts of the heat energy spectrum that can escape to space.  Part of the energy balance  is also moderated by CO2 that absorbs heat in parts of the infrared spectrum that water does not.  Nitrous oxide and methane also play an important role in maintaining the balance between heat that is absorbed, and heat that is redirected to space.  It is worth reiterating that, except for water, the concentrations of these greenhouse gasses are very low and that even minor changes to these amounts will result in some degree of warming or cooling of the atmosphere.

An additional factor in the greenhouse effect is the amount of aerosol and extremely fine particulate matter in the atmosphere.  Volcanic eruptions contribute some of these although addition to the atmosphere is sporadic.  The potential cooling effect from violent eruptions is well documented (Krakatoa 1883, Pinatubo 1991).  Soot from industrial burning and clearing of forests is also present and may influence atmospheric heating.

Although oxygen has no role in greenhouse maintenance, it does interact with certain ultraviolet light frequencies to produce ozone (O3) in the upper atmosphere; this happy circumstance means that most of the harmful UV energy is filtered out by ozone before it reaches the surface.



There is an enduring image of Earth rising above the moon’s horizon, taken during the first manned lunar mission.  Small, cloud swirled, seemingly fragile.  Our atmosphere looks thin.  When you look at this image, and then consider some of the details of how the atmosphere works, the balancing acts among all the gas components, the partitioning of heat and mass from air, earth and oceans, you realize how precarious the conditions conducive to our well-being really are.  I’m not sure who said it first, but it really is all we’ve got.