Moorooduc Estate 2020



Greenhouse Gases and Climate Change


(with extracts from “Science, Music, and Mathematics: The Deepest Connections” by Michael Edgeworth McIntyre. 2022, World Scientific)


My initial incentive to write this document was a feeling of frustration about the public discussion in Australia concerning climate change. Not only do we have a Federal Government heavily influenced by, it would seem, deniers of climate change caused by human activity but we have some otherwise excellent journalists who seem unable to ask appropriate questions on this subject. There is also pressure on media to adopt ‘balanced’ reporting, even if this means giving equal consideration and air time to opposing views when one of these views is absurd, as with the views that ‘the earth is round’ vs. ‘the earth is flat’.


It is difficult for a lay person to have informed opinions on complex matters like climate change. I feel that Michael’s book has given me a much clearer understanding of these crucial matters.


(Michael is my brother. He is an Emeritus Professor of Applied Mathematics at The University of Cambridge. Although his research group has never received funding for climate research as such, his work on atmospheric fluid dynamics, including the dynamics of jetstreams, has made him a close observer of developments in climate science over several decades. He was awarded the Carl-Gustaf Rossby Research Medal in 1987 by the American Meteorological Society for ‘his original and innovative works furthering our theoretical and conceptual understanding of the stratosphere’. The Rossby Medal is the highest award the Society can bestow upon an atmospheric scientist. Michael is also a Fellow of the Royal Society of London, and was closely involved in sorting out the cause of the hole in the ozone layer.)


The following is in a question and answer structure, hoping to answer questions on climate change that a lay person might ask.


My questions and comments are in standard script and represent the interested lay person. Key questions are in bold standard script. Quotes from Michael’s book are in italics, and represent informed, expert opinion.


What should interested lay people (which include many of the voting public, our politicians and other influential people such as journalists) know about the science of climate change? How can we sort out the truths from the myths? We might be facing an existential crisis and surely, if we are to minimise the consequences, the more of us who have some understanding of what is happening and why, the greater the chance that concerted action will be taken.


Here is Michael’s introductory paragraph in the last chapter  (‘Postlude’) of his book ‘Science, Music, and Mathematics: The Deepest Connections’.


“Journalist to scientist during a firestorm, flash flood, or other weather extreme such as Cyclone Idai or Hurricane Dorian: ‘Tell me, Professor So-and-So, is this a one-off extreme, pure chance, or is it due to climate change?’ Well – once again – dichotomization*  makes us stupid. The professor needs to say ‘Hey, this isn’t an either-or. It’s both. Climate change produces long-term upward trends in the probabilities of extreme weather events, and in their peak intensities.’ This point is, at long last, gaining traction as devastating weather extremes become more frequent and more intense.”


Broadly speaking, then, the climate system can be thought of as a powerful but slowly-responding amplifier with sensitive inputs”.


One of these sensitive inputs is carbon dioxide (CO2) which is especially important.


What are greenhouse gases and what is the ‘Greenhouse Effect’?


Greenhouse gases are good. They help make the Earth more hospitable to life. They keep some of the heat energy from the sun from being lost into space. This is the ‘Greenhouse Effect’ which we learnt about at school.


“The physical and chemical properties of so-called greenhouse gases are well established and uncontentious, with very many cross-checks. Greenhouse gases in the atmosphere make the Earth’s surface roughly 30° C warmer than it would otherwise be. For reasons connected with the properties of heat radiation, any gas whose molecules have three or more atoms can act as a greenhouse gas… Examples include not only carbon dioxide and water vapour, each with three atoms per molecule, but also, for instance, nitrous oxide and methane, with three and five atoms respectively. By contrast, the oxygen and nitrogen molecules making up the bulk of the atmosphere have only two atoms, and are nearly transparent to heat radiation.”


Why is carbon dioxide (CO2) so important?


“One reason for the special importance of carbon dioxide is its great chemical stability as a gas. Other carbon-containing, non-condensing greenhouse gases such as methane tend to be converted fairly quickly into carbon dioxide. Fairly quickly means within a decade or so, for methane. And of all the non-condensing greenhouse gases, carbon dioxide has always had the most important long-term warming effect, not only today but also during the glacial cycles. That’s clear from its chemical stability and from the ice-core data, to be discussed below, along with the well-established heat-radiation physics…”


What about water vapour? There’s so much more of it. So surely it’s far more important than carbon dioxide?


“The role of water vapour is also central but entirely different.  It too is chemically stable and has great importance as a greenhouse gas. But, unlike carbon dioxide, it can and does condense or freeze, in vast amounts, for instance as cloud, rain, and snow, while copiously resupplied by evaporation from the tropical oceans and elsewhere. This solar-powered supply of water vapour – sometimes called ‘weather fuel’ because of the ‘latent’ heat energy put in by the Sun and released on condensing or freezing** – dwarfs any human input and makes it part of the climate-system amplifier’s power-supply and power-output circuitry, rather than its sensitive input circuitry.


“Air can hold six or seven percent more weather fuel for every degree Celsius rise in temperature…So global warming is also global fuelling.


“Some of the amplifier’s power output drawing on weather fuel takes the form of tropical and extratropical thunderstorms and cyclonic storms, including those that produce the most extreme rainfall, flooding, and wind damage.  The latent energy released dwarfs the energies of thermonuclear bombs.  Cyclone Idai, which caused such devastation in Mozambique, and Hurricane Dorian, which flattened large areas of the Bahamas, and other recent examples – including the typhoons impacting the Philippines – remind us what those huge energies mean in reality.”


Extremes go in both directions because more weather fuel makes the whole climate system more active and vigorous. Extreme weather events in the early stages of global warming have long been predicted. (For example, in Tim Flannery’s  ‘We Are The Weather Makers – the story of global warming’, 2006.) We are seeing these all the time but the climate change deniers seem not to have noticed.


“Climates have been changing for thousands of years”. So I have heard, as if this dismisses the issue. If the greenhouse effect is good and the climate is changing all the time, what’s all the fuss about?


In part, the fuss is about the speed of change. Most climate change in the past has been much more gradual than the current one threatens to be, generally allowing evolutionary adaptations to take place.


Atmospheric CO2 levels have fluctuated between roughly 180 and 280ppmv (parts per million by volume) over the last 400,000 years until the industrial revolution. (We have an 800,000 year record from Antarctic ice core samples which indicate global temperatures and atmospheric CO2 levels, but only the most recent half of it shows the full 100ppmv range – see appendix.)  CO2 levels have now risen past 400ppmv and continue to rise. This much faster time scale (since the industrial revolution) corresponds with humans burning more and more fossil fuels. Coincidence? I don’t think so.


The first point to note is that human activities are increasing the carbon dioxide in the atmosphere by amounts that will be large. They’ll be large in the only relevant sense, that is, large by comparison with the natural range of variation of atmospheric carbon dioxide with the climate system close to its present state.


The natural range is well determined by the Antarctic ice-core data, recording how atmospheric carbon dioxide varied over the past several hundred millenia. That’s one of the hardest, clearest, most unequivocal pieces of evidence we have. It comes from the ability of ice to trap air, beginning with compacted snowfall, giving us clean air samples from which carbon dioxide concentrations can be reliably measured, exploiting the chemical stability of carbon dioxide as a gas…


In round numbers the natural range of variation of atmospheric carbon dioxide, across the last four glacial cycles, is of the order of 100 ppmv, parts per million by volume. Atmospheric carbon dioxide increased by amounts of this order each time the system underwent a so-called ‘deglaciation’ – a transition from the coldest to the warmest conditions.


“The increase since pre-industrial times now exceeds 120 ppmv. In round numbers we’ve gone from a glacial 180 ppmv through a pre-industrial 280 ppmv up to today’s values, well over 400 ppmv... And on current trends … values will have increased to 800 ppmv or more by the end of this century. An increase from 180 to 800 ppmv is an increase of the order of six times the natural range of variation. Whatever happens, therefore, the climate system will be like a sensitive amplifier subject to a large new input signal, the only question being just how large.”


Why do so many of our leaders dismiss the concept of human induced climate change linked to increasing levels of CO2 in the atmosphere? The vast majority of scientists accept the concept. Why would any sane person not at least take out some ‘insurance’ against the possibility that it is true? Would you not insure your house against fire until you were 100% convinced that it would burn down? Why do we not embrace moving to existing and rapidly developing technologies that do not involve burning fossil fuels, especially now that the new technologies are becoming cheaper than fossil fuels? After all, “the Stone Age did not end because we ran out of stone” – not my original idea, but well worth repeating.


Michael believes that vested interests have been running a disinformation campaign similar to campaigns associated with the links between tobacco and lung cancer and the cause of the hole in the ozone layer.


“In recent decades there’s been a powerful and well-funded series of disinformation campaigns on climate, aimed at promoting fossil-fuel burning and its subsidization… For me it’s a case of déjà vu, because the earlier ozone disinformation campaign –  which I encountered at close quarters during my own professional work – was strikingly similar.


“It’s been known for some years now that the similarity was no accident. According to extensive documentation discussed in Oreskes and Conway (2010)1 – including formerly secret documents exposed through anti-tobacco litigation – the climate disinformation campaigns were seeded, originally, by the same professional disinformers who masterminded the ozone campaign and, before that, the tobacco companies’ lung-cancer campaigns. The secret documents describe how to manipulate the news media, pressing binary buttons and spreading confusion in place of understanding.


“For climate the confusion quickly spread into a number of scientific communities including some influential physicists who weren’t, to my knowledge, among the professional disinformers and their sponsors but who tended to focus too narrowly on the shortcomings of the climate prediction models, ignoring the many other lines of evidence.”


The scientific method has been an extraordinarily powerful tool that is widely misunderstood. Non-scientists often think that scientists think they know everything when in fact, the opposite is the case. Not only is the recognition of ignorance fundamental to science, but every new understanding in science generally opens up many more questions. The more I know, the more I don’t know.  Michael’s book is careful to distinguish between what is practically certain about climate change, and what is less certain, such as how close we are to a tipping point.


When the term ‘tipping points’ is used in the context of climate change, what does it mean?


Here we are talking about ‘feedback mechanisms’.


Biological systems, for example, need to have relatively stable conditions to function. For these stable conditions to be achieved ‘negative feedback’ is required. One illustration is when conditions are very warm, we mammals are able to counteract this by cooling our bodies – dogs pant, humans sweat.


‘Tipping points’ are conditions where a fast ‘positive feedback’ mechanism is initiated. One example here relates to methane gas trapped in frozen ground – ‘permafrost’. As temperatures rise due to rising levels of greenhouse gases, the frozen ground melts releasing increasing amounts of methane which increases the amount of greenhouse gases in the atmosphere. This further increases greenhouse warming, causing more melting and the release of more methane and so on.


Another clear example is the way the reduction in the area of Arctic sea ice, due to the warming climate, increases the absorption of heat from the Sun. (Ice reflects more heat than open water.)


These are two of the ways in which the climate system behaves like an amplifier.  A ‘tipping point’ involves a relatively sudden increase in input sensitivity.


Are there other factors that contribute to changes in the climate?


What about changes in the earth’s orbit around the Sun and the tilt angle of the earth’s axis of rotation?


These become important when we look at the climate system on far longer timescales and, as we will see, even though small they can initiate significant changes in the climate under certain circumstances.


“As for the orbital changes, they’re well known and have been calculated very precisely and very securely over far greater timespans. Such calculations… are possible because of the remarkable stability of our solar system’s planetary motions. The orbital changes include a small oscillation in the tilt of the  Earth’s axis – typically between angles of about 22° and 24°, repeating every 40 millenia or so…”   


The orbital changes together cause fluctuations in the solar heating at high northern latitudes, with peaks and troughs following each other every 11,000 years or so. One gets a peak when the Earth is closest to the Sun in northern midsummer. About one in five of the peaks, over the last 400,000 years, corresponds to the start of a period of deglaciation from an ice age, in which sea levels rise by well over 100 metres. Why only one in five? The reason is that the system needs to be fully ‘primed’ for deglaciation to be the result. Two priming mechanisms occur in the coldest conditions.


“One is that the system became more sensitive when it was fully primed for the next big carbon-dioxide injection. To become fully primed it needed to store enough carbon in the deep oceans. Storage was favoured in the coldest conditions, which tended to prevail during the millennia preceding full deglaciations…


“Also important was a different priming mechanism, the slow buildup and areal expansion of the great northern land-based ice sheets. The ice sheets slowly became more vulnerable to melting in two ways, first by expanding equatorward into warmer latitudes, and second by bearing down on the Earth’s crust, gradually taking the upper surface of the ice down to warmer altitudes. This ice-sheet-mediated priming mechanism made the system still more sensitive.”


What about the Sun?


I have heard it said with great confidence that the warming climate is caused by sunspot activity (on the Sun). Like most people I have no knowledge of my own to refer to on this topic so I will defer to an informed scientist, my brother Michael, who as it happens, has worked on solar physics as well as on phenomena in the Earth’s atmosphere. Prior to the following passage, he writes about the increasing power output of the Sun, increasing by about 1% every one hundred million years. And on shorter timescales,


“Variability in the Sun’s output on timescales much less than millions of years comes from variability in sunspots and other magnetic activity near the Sun’s visible surface. Such activity is a by-product of the turbulent, boiling fluid motion caused by thermal convection in the Sun’s outer layers… The variability is now known to have climatic effects distinctly smaller than the effects of carbon dioxide injections to date, and very much smaller than those to come.


“ The climatic effects from solar magnetic activity include a direct response to the resulting slight variability in the Sun’s power output, together with some small and subtle effects from a greater variability in the Sun’s ultraviolet radiation, which the Earth absorbs mainly at stratospheric and higher altitudes when the ozone layer is intact… Controversially, there might be an even more subtle effect from cloud modulation by cosmic-ray shielding, which varies with solar magnetic activity.


“But along with their smallness, the timing of all these effects, which wax and wane every 11 years or so in what’s called the ‘solar cycle’, implies that they have no more than marginal relevance to any of the longer-term climate changes I’ve been discussing.”


In response to the question “What’s all the fuss about?” I suggested that the fuss was about the speed of climate change.


That was an incomplete answer because, at whatever speed we warm the climate, we could be creating highly undesirable conditions for human civilisation, with sea levels for instance ending up about 70 metres higher than today, as they were in the early Eocene.


The Eocene epoch (56 to 34 million years ago) was a time when a large amount of volcanic activity was likely to have resulted in high atmospheric CO2 levels, maybe in the thousands of ppmv. (Unlike the most recent 800,000 years, we have no direct data to confirm CO2 levels as such, though there are plenty of data to show that temperatures were much higher than now, with no great ice sheets at all and sea levels much higher, in the order of 70 metres.)


If atmospheric CO2 levels continue to rise, it is a real possibility that, because of the positive feedback mechanisms (tipping points) discussed previously, conditions similar to those that existed in the Eocene epoch could happen again. If so, the time to reach these conditions would most likely be a number of centuries from now, but there is great uncertainty about this prediction.


“…,it’s even possible that the system might go into runaway climate change towards a very hot, very humid state like that of the early Eocene around fifty million years ago…The end result would be first that there’d be no great ice sheets at all, even in Antarctica, second that sea levels would be around 70 metres higher than today, and third that the strongest thunderstorms would probably be far stronger than today …


“And it was just then [in the early Eocene] – surely no accident – that some land-based mammals began to migrate into the oceans. Within several million years, some of them had evolved into mammals that were fully aquatic, precursors to today’s whales and dolphins. Selective pressures from extremes of surface storminess can make sense of those extraordinary evolutionary events …”


If you have found the above interesting, informative and/or thought provoking I encourage you to read some or all of Michael’s book, “Science, Music and Mathematics: The Deepest Connections” published by World Scientific, 2022, especially the Postlude, and references in Chapter 3 to ‘Dansgaard-Oeschger cycles’. (These are transient, abrupt warming events recorded over the last 50,000 years in Greenland ice cores).


The book covers these and other subjects in great detail as well as having an extensive bibliography.


An unusual aspect of the climate change conversation is that, unlike other complex, specialised subjects, a wide range of people with little or no credentials to do so, have strongly held views which they wish to impose on the rest of us. (Who would, for example, seek advice from a lawyer or an accountant on how to manage a brain tumour)?


Perhaps, contributing to this state of affairs has been the brief to the IPCC (Intergovernmental Panel on Climate Change) to come up with ‘definite predictions’ of the incredibly complex system, using climate (computer) models that, according to Michael, are useful in some ways but cannot, for instance, simulate the full complexity and, in particular, extreme storminess – which requires far more than the available computing power.


Michael believes that these big climate models are getting better but he thinks we should pay more attention to the longer time scale patterns as exemplified by the 800,000 year records from Antarctic ice cores, and many other palaeoclimatic lines of evidence.


We need our political leaders, our journalists and, most of all, our voting citizens to have a better understanding of the high risk to the future of our species, and many other plants and animals on this planet, by continuing to harvest and burn fossil fuels, especially when much better, safer, and cheaper technologies are here or on the near horizon.


Remember, the Stone Age did not end because we ran out of stone.


Richard McIntyre, MB BS (Monash), D Phil (Oxon), FRACS.





*    Michael is referring here to:  “…the dichotomisation instinct, the primitive binary button that journalists and politicians keep on pressing to get us polarised. Dichotomisation, in this sense, is the visceral urge to see only two opposing choices and to decide between them without stopping to think, an ancient survival instinct – as with fight or flight, edible or inedible, male or female, friend or foe – but today an obstacle to clear thinking.”


**    The technical term for this thermal energy is ‘latent heat’, the heat released, in this instance when water vapour condenses to make water, or when liquid water freezes to make ice.  During such processes, called ‘phase changes’, the heat comes out even when the temperature stays exactly the same.  Conversely, when the phase change is in the other direction (liquid to vapour or solid to liquid), heat must be supplied, as when boiling away the water in a kettle (the temperature staying at about 100° C) or when evaporating water from a warm ocean (with the temperature changing only a little, thanks to the enormous heat capacity of the ocean).



  1. Oreskes, N. and Conway, E.M., 2010: Merchants of Doubt: How a Handful of Scientists Obscured the Truth on Issues from Tobacco Smoke to Global Warming. Bloomsbury, 2010

  2. Lüthi, D., et al., 2008: High-resolution carbon dioxide concentration record 650,000-800,000 years before present. Nature 453, 379-382





Included are two charts, the first one from Michael’s book (with its Legend) and the second one from the American website, NOAA


The discussions relevant to the first chart, which is complex and a bit confusing, are in the main text above. Time runs from right to left. We should concentrate on the two separate graphs, the upper one showing temperatures and the lower one CO2 levels. The only other important features for our purpose are TIX to TI, which indicate the times of major deglaciation from an ice age. These were triggered when the temperatures and the atmospheric CO2 levels were low.



Figure. Antarctic ice-core data from Lüthi et al. (2008)2  showing estimated temperature (upper graph) and measured atmospheric carbon dioxide (lower graph). Time, in millennia, runs from right to left up to the present day. The significance of the lower graph is discussed in the Postlude. The upper graph estimates air temperature changes over Antarctica, indicative of worldwide changes. The temperature changes are estimated from the amount of deuterium (hydrogen-2 isotope) in the ice, which is temperature-sensitive because of fractionation effects as water evaporates, transpires, precipitates, and redistributes itself between oceans, atmosphere, and ice sheets.  …  The `MIS’ numbers denote the `marine isotope stages’ whose signatures are recognised in many deep-ocean mud cores, and `T’ means `termination’ or `major deglaciation’. The thin vertical line at around 70 millennia marks the time of the Lake Toba supervolcanic eruption”.


The second chart only shows atmospheric CO2 levels over 800,000 years, in this instance, with time running from left to right, but shows clearly the current spike of CO2 levels – >400 ppmv and still rising.



What it doesn’t show, unlike the first chart, is the correlation between the small changes in the CO2 levels and the huge changes in climate during the roughly 100,000 year glacial/interglacial cycles.


During the past 800,000 years there were nine major deglaciations from ice ages (T1X – T1), triggered by orbital changes acting on a primed system, CO2 being injected into the atmosphere from the deep oceans. On each occasion the major deglaciation was triggered when the atmospheric CO2 level was at its lowest. This is discussed above.


The temperature changes (shown in the upper graph) which correlate with the changing levels of CO2 don’t seem huge at first glance but a 10°C shift is in fact huge, and the climatic conditions of an ice age were vastly different from the conditions after major deglaciation. For one thing, the sea level difference was in the order of 100m and for another, vast areas of the great northern land masses were, during ice ages, covered with huge glaciers several kilometres thick.


So these relationships demonstrate the ‘amplifier metaphor’ and give credence to the warning that the bigger changes in CO2 levels in the atmosphere that we are seeing already, are likely to produce very large changes in the climate – Michael’s main message.

Share this post