Just Breathe
The route from my house which follows the road to Hethpool and the College Valley is a favourite and regular running route for me. From Kirknewton the road runs past the village hall and St Gregory’s, the (originally) 12th century parish church with its famous kilted-magi. Beyond this there are flat, flood-plain fields bounded by steep hills, and the old railway-station houses. Shortly before Westnewton the road crosses the College Burn, just upstream of its confluence with the River Bowmont, the combined rivers flowing on down Glendale as the River Glen.
In Westnewton the road to the College Valley turns off the main road and past the large Edwardian house of the Kirknewton Estate now owned by Simon Douglas-Hume (an interesting merger of two reiving family names). To reach the College Valley the road takes a detour up around the Bell (a hill!) west of the College Burn before reaching a saddle at 500 foot and then dropping down to Hethpool and into the College Valley. This glacial valley, one of the most beautiful in the Cheviots, runs right the way up to the Border Ridge between the Cheviot itself and the Schil and offers the best route onto the Cheviot via Hen Hole.
On the way back I like to push myself, after the long run downhill in the College Valley, to a fast run up the saddle by the Bell before easing into the final run-out back down to Westnewton and then home. It always strikes me, when I get to the top of the saddle having pushed hard to that point, that as I relax into the downhill that my breathing continues to get harder. There is a time-lag between reducing the effort put into running and my breathing rate, maybe a consequence of an oxygen debt built up, with the body requiring time to adjust to the new level of effort.
Change in breathing-rate is one of many processes which have an associated time lag. The slow increase in the sea’s temperature lags behind the warmth we feel in the air as the sun’s radiance warms through Spring. The sun that we look at (through dark glasses) is the sun of 8 minutes ago, as even at the speed of light it takes this long to travel the 193 million miles in between.
The operation of our planet’s geological, biological and atmospheric processes and the interaction between them contain several examples of this type of lag.
Perhaps the earliest and most protracted of these was the first development of oxygen in the atmosphere, way back in the Archaean. This event was not only crucial to my very existence, but also my ability to run up hills, with the energy released by oxidation powering my fast metabolism as well as that of all multi-celled organisms and most single-celled organisms. This time lag is between the evolution of oxygenating bacteria and the oxygen they create arriving in the atmosphere. Some 3.5 billion years ago (that’s one thousand times older than the Carboniferous rocks which underpin Hadrian’s Wall) in the early Archaean the atmosphere had an unquantified mix of nitrogen, carbon dioxide, methane and ammonia. What we do know is that there was no oxygen in this atmosphere, as iron on the surface didn’t rust.
What was needed was something that would break out the oxygen contained in atmosphere’s CO2. This something evolved early in the Archaean as cyanobacteria, which could use iron and CO2 mixed with the energy of sunlight to grow their bodies. There were, however, other blocks in the pathway to releasing oxygen into the atmosphere. The first was that the earliest cyanobacteria didn’t make free oxygen, they made iron oxide instead. This, however, was not a problem, as the second block was an oceanic addiction to iron, which dissolves readily in seawater in the absence of oxygen. This mass of dissolved sea iron meant that any oxygen created simply reacted with the dissolved iron, which promptly precipitated as iron oxide and sank to the bottom. Our early cyanobacteria, by making iron oxide as a by-product, were steadily mopping up this dissolved iron.
By the time cyanobacteria evolved to produce free oxygen later in the Archaean, there was less dissolved iron to steal this oxygen. By the end of the Archaean and moving into the Proterozoic Era 2.5 billion years ago, free oxygen arrived in the atmosphere and the surface of the earth started to rust. This was an unimaginably slow process, taking a billion years, 3 times longer than the length of time between our Carboniferous rocks and the present.
The consequences were immense, providing the starting point for the evolution of life as we know it as well as depositing massive quantities of iron. These deposits consist of finely banded layers of iron oxide (haematite) and chert and is known as the banded iron formation. This is by far the most important source of iron used by homo sapiens.
Oxygen also features in a delayed response nearer to home and nearer in time, in which evolution and geology feature once more. This is the time lag between the arrival of plants on the land surface and radical changes in atmospheric O2 and CO2 during the Carboniferous Period.
Imagine finding a centipede under a rock. Now imagine that centipede is over 2m long and half a metre wide. This is what happened to a Cambridge research student a few years ago, on a walk along the shore at Howick on the Northumberland coast. Admittedly the creature was a long time dead, having been preserved in one of the silty sandstones of the Carboniferous period which crop out on the coast here. Nonetheless it was spectacular find, being the largest specimen of a creature named Arthropleura which has ever been found. This gigantism is a feature of many groups of Carboniferous animals. It is particularly surprising to find such a large arthropod which group of animals respires by diffusion through its skin. This is one line of argument indicating that during parts of the Carboniferous period the levels of oxygen in the atmosphere exceeded 30%, compared to current levels of 21%. With that amount of oxygen my run up the College Valley would have been at a solid road-runner pace – meep meep!
The size of the Howick Arthropleura specimen, which comes from the middle Carboniferous, has been compared to that of specimens from various times earlier in the Carboniferous. This shows a progressive increase in the size of the animals which is thought to relate to the progressive rise in oxygen levels in the atmosphere. At the same time, we know that the levels of CO2 in the atmosphere decreased, and after a lag in time, the global climate also became cooler. This cooling has strong evidence from glacial deposits – tillites – which show that ice-caps formed during this period. Why was the atmosphere changing? It seems that once more we have evolution to thank, but this time in plants.
Plants had colonized the land surface many millions of years before the Carboniferous. Fossil liverworts have been found in the late Silurian period (at 425 million years old) and recent research using DNA suggests that there may well have been land plants some 100 million years earlier, during the Cambrian Period. No doubt these plants started to contribute to the removal of CO2 and the generation of O2 as they grew and respired. So why the long delay before the effect is seen in the Carboniferous Period, both in the atmosphere and in the climate? Three possible reasons stand out.
The first is the presence of lignin, which had evolved by the beginning of the Carboniferous Period. Lignin decays more slowly than softer plant tissue. Additionally, fungi which now break down lignin may not have evolved in the Carboniferous Period. This meant that at that this time more dead wood was taken out of circulation through burial by sediment rather than by oxidisation and consequent release of CO2 back into the atmosphere.
The second reason follows in part from the presence of lignin. During the Carboniferous significantly more of the land surface became colonised by plants in terms of the land surface and ecological niches covered as well as by the sheer size of the plants. The giant lycopods which were one of the major plant types of the Carboniferous not only grew to many tens of metres in height but also had a phenomenal growth rate. Together this means that the volume of carbon-rich plant material available for burial vastly increased at this time.
The final reason is linked to the changes brought about in the atmosphere, in particular the very high levels of oxygen. The progressively more devastating wildfires seen in California and Australia are awe-inspiring and terrifying to watch. However, this would have been a whole lot worse and much more frequent with an oxygen-rich atmosphere. The Carboniferous forests were frequently on fire which meant that large amounts of charcoal were produced. Charcoal decomposes much more slowly than wood and other plant tissues and more of it gets buried. So, whilst the fires themselves turned oxygen and trees back into CO2 the charcoal meant that much more of the trees’ carbon was buried and taken out of the carbon cycle (at least until the present day!).
The ice caps that formed during the Carboniferous Period disappeared towards the end of the period over 300 million years ago. They didn’t return until about 2.5 million years ago. There is much evidence we can glean from rocks and fossils of the Carboniferous period regarding climate change. However, the data available on climate change from our recent past is much more detailed. Now and in our recent history we have been measuring changes in climate around the world and the impact this had on natural processes. To go further back there is a geological record forming, for example, in the form of layers of sediment at the bottom of lakes and in the sea; much can be learned from these. There is also another more ephemeral (in geological timescales) source of information, which is ice. Snow is seasonal and as it falls, snow on snow, in the Arctic and Antarctic areas and slowly compacts forming annual layers which can be read back like the rings of a tree. Within the ice, bubbles of the atmosphere become trapped so that it is possible to see changes in CO2 levels along with other atmospheric components. There is a lag in this process too, as it takes many years for the snow to compact sufficiently that the air bubbles are sealed in. The date the snow is laid down and the age of the atmosphere it eventually traps are different by a few hundred years.
Not only is it possible to analyse historic changes in atmosphere, but analysis of the oxygen and hydrogen isotopes in the ice also tell of the temperature when the ice formed. Between these analyses it is therefore possible to build up a detailed picture of the relationship between temperature and carbon dioxide. This month’s mystery rock is one of many ice-cores recovered from the Arctic and used for this purpose. Analyses of these ice-cores reveals a lock-step relationship between temperature and CO2; when temperature is higher so is CO2 and vice versa.
There is however another time-lag here. When the temperature rises, there is a delay before CO2 levels start to rise. It is a mantra of scientists that correlation doesn’t necessarily mean causation, and some people use this stick to discredit the idea of manmade climate change; if CO2 rises after temperature increase, then is can’t be the cause of that temperature change. However, the reality is much more complex.
There is no doubt that an increase in CO2 causes global warming as it is a physical property of the gas, but there is another cause for changes in global temperature. This is to do with the amount heat we receive from the sun which varies over time. The earth’s rotation around the sun is not fixed and constant but wobbles ever so slowly and in several different ways. Firstly, the earth’s orbit is an ellipse, and not a circle, and furthermore the shape of that ellipse (the orbital obliquity) changes over time between something more circular and something more elliptical. Secondly the earth’s axis is tilted, a fact which gives us our seasons, and both the amount of tilt (axial tilt) and its orientation towards the sun change over time (axial precession). Each of these wobbles mean that the amount of heat the earth captures from the sun (its insolation) changes progressively and predictably over time. The sums to make those predictions were first carried out, meticulously and laboriously in a pre-computer age, by a Serbian mathematician Milutin Milankovitch. These Milankovitch cycles as they have become known correlate precisely with changes in global temperature. It now seems clear that increases in global temperature are initiated by the changes in insolation described by the Milankovitch cycles. As the temperature rises, this causes more CO2 to be generated which then significantly amplifies the initial increase in temperature.
This brings us back to the present day, cooling down in my garden with a large glass of elder cordial in hand contemplating what happens next. What can be predicted of where global climate is heading from our knowledge of Milankovitch Cycles and the detailed record of our immediate past which the ice cores give us? Even with all of this data it seems that this is hard to predict. It is likely that without manmade CO2 there will come a point in the next 10 to 40 thousand years that the global climate cools. However, that manmade CO2 is there in quantities not seen for over 2.5 million years.
At that time there were no icecaps, and the sea level was over 100 feet higher than it is now. Our contribution to atmospheric CO2 continues to grow in volume.
The peat at Vindolanda and other locations along the Wall is drying out owing to the dryer warmer climate being experienced in this part of the world, a likely in consequence of manmade climate change. It may well be that the delicate leather and wood artefacts so beautifully preserved by the peat will start to oxidise as the drying continues and deny us the wonder and information they bring. Just one small consequence of the direction of travel we see emerging.
At this point I wonder at mankind’s collective action in the time-lag between continuing to create atmospheric CO2 and its likely consequences. It seems rather like the time-lag in the ever-outwitted Wylie Coyote as the slow grinding of his mental cogwheels finally give him the dawning realisation that he is running in thin air, shortly before plummeting into the canyon below.
Attributions
The idea for this blog was inspired by a reading of “The Goldilocks Planet” by Jan Zalasiewicz and Mark Williams. For much more detail about some of the ideas presented here (and somewhat simplified) this is an excellent and readable book.
Ice Core: This photograph shows a section of the GISP2 ice core from 1837-1838 meters in which annual layers are clearly visible. The appearance of layers results from differences in the size of snow crystals deposited in winter versus summer and resulting variations in the abundance and size of air bubbles trapped in the ice. Counting such layers has been used (in combination with other techniques) to reliably determine the age of the ice. This ice was formed ~16250 years ago during the final stages of the last ice age and approximately 38 years are represented here. By analyzing the ice and the gases trapped within, scientists are able to learn about past climate conditions. Soerfm, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
The sun: NASA, Public domain, via Wikimedia Commons: This photograph of the Sun, taken on December 19, 1973, during the third and final manned Skylab mission, shows one of the most spectacular solar prominences ever recorded, spanning more than 588,000 kilometers (365,000 miles) across the solar surface. The loop prominence gives the distinct impression of a twisted sheet of gas in the process of unwinding itself. In this photograph the solar poles are distinguished by a relative absence of supergranulation network, and a much darker tone than the central portions of the disk. Several active regions are seen on the eastern side of the disk. The photograph was taken in the light of ionized helium by the extreme ultraviolet spectroheliograph instrument of the U.S. Naval Research Laboratory.
Cyanobacteria: TEM image of ”Prochlorococcus marinus”, a globally significant marine cyanobacterium : Luke Thompson from Chisholm Lab and Nikki Watson from Whitehead, MIT, CC0, via Wikimedia Commons.
Banded Iron Formation: Banded Iron Formation at the Fortescue Falls, Karijini, Australia: Graeme Churchard from Bristol, UK, CC BY 2.0 <https://creativecommons.org/licenses/by/2.0>, via Wikimedia Commons
Arthropleura: Artist’s impression of Arthropleura (which has some anatomical inaccuracies, but gives a good idea of scale). Tim Bertelink, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
Arthropleura size comparison: from Davies etal 2021, Journal of Geological Science. The Largest Arthropod in Earth History.
Wildfire: Elk in the Bitterroot River at Sula, Montana, during a fire in the year 2000. Photo by John McColgan, fire behaviour analyst with the BLM’s Alaska Fire Service: John McColgan – Edited by Fir0002, Public domain, via Wikimedia Commons
Graph of CO2 v Temperature: This shows historical carbon dioxide (right axis) and reconstructed temperature (as a difference from the mean temperature for the last 100 years) records based on Antarctic ice cores, providing data for the last 800,000 years. Leland McInnes at the English-language Wikipedia, CC BY-SA 3.0 <http://creativecommons.org/licenses/by-sa/3.0/>, via Wikimedia Commons
Milutin Milanković: Unknown author, Public domain, via Wikimedia Commons
Vindolanda letters: Roman writing tablet from the Vindolanda Roman fort of Hadrian’s Wall, in Northumberland (1st-2nd century AD). Tablet 343: Letter from Octavius to Candidus concerning supplies of wheat, hides and sinews. British Museum (London): British Museum, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
Figure 6. (a)-(e) Geological epochs and earth atmospheric temperature (˚C, ˚F vs. 1960-1990 avg.) (Bredenberg, 2012).
Figure 7. CO2 and temperature over past 420,000 years (Watts & Pacnik, 2012).