Today we are deeply conscious that the enthusiasm of our forebearers for the marvellous achievements of Newtonian mechanics led them to make generalisations in this area of predictability which, indeed we may have generally tended to believe before 1960, but which we now recognise were false. We collectively wish to apologise for having misled the general public by spreading ideas about the determinism of systems satisfying Newtons laws of motion that, after 1960, were proven to be incorrect...”-- Sir James Lighthill. Lighthill spoke at a conference marking the 300th anniversary of Newtons Principia and his reference is to the development of chaos theory which actually started well before the turn of the last century, but was overshadowed by more impressive developments in quantum mechanics and relativity. Chaos theory helped to clear scientists illusion about the absolute predictability of deterministic systems and spared them the futile efforts of searching for analytical solutions to all problems that obey Newtons laws. They discovered, perhaps by accident, that even the simplest systems can exhibit chaos if one can wait for a sufficiently long time. Chaos as understood in physics and mathematics has nothing to do with randomness, but it indicates how a small error in initial conditions can lead to a result far away from the expected one. As a simple example one can consider the summation of, say, 2 million numbers that involve decimal places. If one discards 0.001 form each number as an approximation, there will be an error of 2000 in the end, and so will the error increase as the data points increase. Chaos theory is relevant to climatology in many ways. One is that it makes long term predictions unreliable or rather hopeless; sensitivity of systems to initial conditions was indeed discovered when solving differential equations on turbulence associated with global weather, hence the term butterfly effect coined to describe it. In another way,chaos in the Solar System affects the geometric relationship of planets with the Sun, particularly the Earth; a situation that brings about a variation in solar radiation reaching the Earth and, hence, in global climate. The major breakthrough and indeed the actual beginning of serious studies in chaos theory and chaotic dynamics is Poincares discovery that there can be no analytical solution to the solar system as a mechanical problem of more than two bodies interacting through a central force. He simply asserted that the solar system is chaotic. Poincare was answering a challenge to European mathematicians which demanded from them, among other things to prove that the solar system is stable. Newton of all times asserted that only Divine intervention can be the principle behind the stability of the solar system! With this fitting and necessary introduction I humbly proceed to present to you my views on climate change. I am, in no way, claiming originality, I am simply trying to put together the existing and prevalent views in the mainstream scientific community as opposed to the celebrated campaigns propagated by well intentioned environmental activists. There are many lines of argument among the scientists, but the ones I want to present here are the most generally accepted ones among genuine scientists. In climatology, like many other fields such as cosmology and anthropology, knowledge of the past enables researchers understand the present better and make projections into the future. However, humancivilisation started just a moment ago on the geological time-scale so that man has not witnessed anything substantial of the Earths climate to make generalisations. In spite of this,it is customary in science to rely upon the limited observations in the present and, by guidance of principles, extrapolate to the distant past. This is what makes cosmology and geology, among others, very exhilarating, and a special branch of geology dedicated to the study of ancient climates has thus emerged with the name palaeoclimatology. Past climates have left their signatures and dates engraved on landmarks, in deep sea core sediments and in faunaland floral remains all over the Earth. The composition, type and proportion of certain chemicals or plants, as the case may be, serve as proxy thermometers that enable palaeoclimatologists measure temperatures of the distant past. The most accurate and, so far, the most widely used proxy thermometer is the oxygen isotope ratio. It is so reliable because it does not depend on decay or chemical processes but on simple dynamical principle; the difference in mass between two types of oxygen atoms-isotopes. It is the principle exploited in the enrichment of uranium fuel. The most common oxygen atom has 8 protons and 8 neutrons hence it is called oxygen-16 or light oxygen. There is another oxygen atom with 8 protons and 10 neutrons hence it is called oxygen-18 or simply heavy oxygen because it is slightly heavier than the former. The later is very rare; found only in about 1 atom per 500 atoms of oxygen. However, they both combine with hydrogen in the same proportion to form water. At lower temperatures, when molecules have lower kinetic energy, water containing light oxygen is more likely to evaporate, so there is more of it in the atmosphere to form snow which later falls to form ice sheets. When the temperature is higher, even the molecules of water containing heavy oxygen will gain enough energy to escape from the surface of the sea into the atmosphere. So ice sheets formed during cold climates have lower proportions of heavy oxygen and sea water of the same time has higher proportion of it; reverse is the case, ice formed in warm climates has higher proportion of heavy oxygen and sea water of the same time has lower proportion of it. This technique is so fine and reliable that a rise in the proportion of heavy oxygen by one part per million in ice or sea water represents, almost, exactly 1.5c rise or fall in global temperature respectively and vice versa. The oxygen isotope ratio is calculated from samples of ice obtained from drills in either the Arctic or the Antarctic region. From early 1950s to date, governments of USA ,USSR and France have, among others, sponsored various expensive ice drilling projects. Among the most notable are the Camp Century expedition to Greenland, the Byrd Station and the Vostok Station projects both on Antarctica. These expeditions were almost deadly, but they have brought astonishing revelations from data dating back to some million years ago so that most scientists, said one of them, have come to accept the most incredible; the existence of ice ages in the past. Another reliable source of oxygen isotope data is that of shells of sea creatures that once lived near the surface and drank the sea water in their lifetimes. The oxygen in the carbonate of which their shells are made tells whether the water they drank had more or less heavy oxygen- Newton should have known that picking sea shells is a sophisticated science! The collection of these animal remains is done by drilling deep into the ocean core sediments and is as tedious and dangerous as the collection of ice samples from Greenland or Antarctica. It is the analysis of the data so collected that revealed the compelling incredible; that there have been not only one but dozens of ice ages in the past. Not only that, it also revealed that there had been periods so warm that the Earth had almost no ice sheets at all; and periods when many habitable places of our days were covered by water and at other times by ice! And that these trends are cyclic!! The temperatures so measured are dated by various techniques the most accurate precise of which is the radiocarbon dating which, unfortunately, has a serious limitation. It measures dates only to some tens of thousands years back while geologists are interested in dates some hundreds of millions years back, so in such cases they resort to alternatives such uranium-thorium technique and stratigraphy among other techniques. Climate cycles are best understood when categorised into three distinct cycle: The long term cycles of period 100 million years characterised by few isolated glacial epochs- the great Ice Ages, the medium term cycles with period of 1 million years characterised by semi regular advances and retreats of glaciers during the last 2.5m years- the Pleistocene period, and the short term changes whose periods are relatively too short- 100000 years-160000 years. Thus on a graph, taking the long term cycle as a background, the pleistocene will appear as a saw-tooth function with major cycles of about 100000 years or so periods on which are superimposed shorter and more complex cycles of nearly 41000 and 25000 year periods. It will also indicate that the present warming started some 15000 years ago when glaciers finally left Michigan in northern USA. What is the cause of such climate cycles? This is where the trouble lies! Any theory that sets out to answer this question must prepare itself to account for such almost regular cycles, and as differing as they are, it is unlikely that a single theory can account for all of them. So, for each cycle or set of cycles there is a theory, but the failure of one theory to explain another cycle is not an actual failure but limitation and it is acceptable in science; quantum mechanics and classical mechanics have different jurisdictions in physics without the one invalidating the other. This is the same in climatology; a theory may explain the long term cycles and fail to explain the other cycles. The long term cycles seem to be the most challenging. The most popular candidate for explaining them is the greenhouse gas theory-but certainly not from industrial emissions. It relies upon the connexion between continental drift and volcanic actions. Proponents of the plate tectonics theory argue that 300 million years ago, the continents were assembled in single super continent known as the Gondwanaland land. At that time, they argue, there were fewer plate motion and, hence, less volcanic eruptions that release CO2, a major greenhouse gas,into the atmosphere, and, that at other times there used to be more frequent volcanic eruptions, hence more CO2 and a warming trend sets in. This theory has an insurmountable problem; the analysis of ancient air trapped in glaciers has revealed no rise in CO2 of such proportions in the past. Some authors even attribute the cooling trends to increased volcanic activity as it releases dust particles into the atmosphere. Whether volcanic activity causes cooling or heating, I discard both approaches. I also disregard the cosmic dust theory which attributes the cooling to influx of dust from outer space for I cannot conceive a cosmic event that causes such short cycles( they are very short on the astronomical time-scale). My favourite theory for explaining the long term cycles is the theory of solar variation. I do not mean the 11 year sunspot cycles and the 22 year magnetic cycles, but a longer term variation in the total output of the Sun. A prominent astrophysicist, Ernst Opik, worked out a theory of cyclical variations of nuclear reactions deep inside the Suns core and found fluctuations of 100 million year time-scale: this sounds like the 100 million year climate cycle!He further demonstrated that within a certain glacial epoch, a kind of flickering of solar radiation in the Suns outer shell drives the advance and retreat of glaciers. Thus Opiks theory sets out to solve the entire mystery of climate changeat a blow- to kill all the birds with a single stone, but I disagree because there is a more plausible theory backed by a compelling bank of evidence to explain the short term cycles. Milutin Milankovitch, a Serbian scientist/mathematician, has in the early 1930s, demonstrated how variations in the Earth-Sun geometry affect the amount of solar radiation fallingon, particularly, the Northern Hemisphere and, therefore, global climate. His theory, which came to be known as the Milankovitch Theory or simply MT, is based on three cyclic variations in the orientation of the Earth and its seasonal position with respect to the Sun. The three cycles are called Milankovitch cycles. If the Earth were to be the only planet in the solar system, then, according to Newtonian-Keplerian mechanics it will constantly maintain an elliptical orbit around the Sun, but this is not the case. The Solar system is rather chaotic so that other planets, notably Jupiter, affect the shape of the Earths orbit changingit from a perfect ellipse to nearly a perfect cycle and back to an ellipse again in a period of roughly 100000 years. The degree to which the orbit resembles a cycle or an ellipse is known as eccentricity. A cycle has 0 eccentricity whereas a perfect ellipse has maximum eccentricity of 1. Being the first of the Milankovitch cycles, changein eccentricity alters seasonal variation in sunlight from 20% at minimum eccentricity to 2% at maximum eccentricity. All the oxygen isotope analysis made on ice from Greenland and Antarctica and ocean sediments from the Atlantic and the Indian oceans have strongly suggested 100000 year cycles whose timings are in agreement with variation in eccentricity. The other planets also changethe orientation of the Earth with respect to the plane of its orbit known as the ecliptic. The Earth is slightly tilted with respect to the ecliptic at angle which varies from 22 degrees to 24.5 degrees over a period of 41000 years. The angle of tilt is technically known as the obliquity, and thanks to the presence of the Moon as a stabilising mechanism, obliquity would changethrough 60 degrees in a period of 5 million years! Variation in obliquity is the second Milankovitch cycle and traces of its effects on global climate have been reported in all the analysis where some have reported 40000 year cycles and others reported about 45000 years or so in agreement with Milankovitchs timings. The third cycle is driven by the torque exerted on the Earth by the Sun and the Moon due to the equatorial bulge of the Earth. It is known as the precession or wobbling of the Earths axis of rotation, and it is in the direction opposite the direction of revolution of the Earth hence, it is called retrograde precession. Precession has a period of about 23000 years and its effects have been equally reported in the past global climates. The presence of of these records and their agreement with each other and the Milankovitch predictions cannot be a coincidence, rather it firmly establishes the MT as a valid theory. The only data point that contradicted the MT is that obtained from the analysis of sediments from a desert oasis in Nevada,USA, known as the Devils Hole. The Devils Hole chronology was dated by the uranium-thorium technique which is one of the most accurate dating techniques, but I still consider it imprudent to throw away the MT, which has been confirmed by various data obtained from across the Globe, in favour of some cranky notion of cosmic dust effect. It is better to consider the Devils hole data, which stand alone, as representing only local effects.[ besides, is it not said to be the Devils hole?] Since Milankovitch cycles can simply be computed from celestial mechanics, it would have been easy to predict future climates if they were the only forces behind climate change. Some scientists, such as George Kukla of Czechoslovakia and the US based Italian Caesar Emilliani have done so and predicted that there will be an onset of glaciation very soon( the geologists soon may be a few millenia later). However, such predictions are problematic because despite their strong presence in climate records, the Milankovitch cycles are certainly not the only forces behind climate change. Many other causes seem to be at play, thereby makingthe climate system chaotic and, hence, almost unpredictable. For example, when the present warm era started 15000 years ago, the MT cannot account for the sudden cooling that started about 5000 years later which lasted for only 700 years. Nor can it explain the cold spell that was recorded during the Middle Age Europe which lasted for 300 years known as the Little Ice Age. The most likely cause of these interruptions to the normal Milankovitch cycles is the variation in solar energy output. It is therefore wise to revisit Ernst Opik at this moment because during the Little Ice Age, only few, if any, sunspots were observed. This is why the period is referred to as the Maunder Minimum. The connection between global climate and greenhouse gases is in the fact that the Oceans, the atmosphere and the Sun form a complex thermodynamic system with a delicately poised feedback mechanism such that a rise in global temperature stimulates the oceans to emit more CO2 and when the temperature falls the oceans absorb more CO2. This is, perhaps, how the Milankovitch effects that occur at the Northern polar region are communicated across the Globe. Disputing the arguments of greenhouse effect; Ian Clark, a professor of palaeoclimatology at Ottawa University argued that past climate records show that the increase in atmospheric CO2 lags behind the onset of warming trends by 800 years. He further argued that during the second World War(1939-1945), an upsurge in the amount of greenhouse gases was detected, but the four decades that followed witnessed a cooling effect. The notion of industrial greenhouse effect on global climate is more of political economics than it is of physics or geology and, as a science, it is no more than astrology or the notion of UFOs. An American historian and an activist, Wester Tarpley, called it a pseudoscientific fraud.
Posted on: Thu, 04 Dec 2014 23:55:00 +0000
Trending Topics
Recently Viewed Topics
© 2015