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Sustainable Aviation Fuels (SAF) is about as dull a subject as one can imagine writing about and for you, my one reader, to read. But the hype and quality of the ‘BS’ generated over it is more interesting. In elucidating on that subject, the scope of the discussion inevitably must expand into a wider environmental context and risk ecological excommunication. So here we go………

The Tropopause (the bit we breathe and fly in) is just 12 miles thick – the distance of a healthy walk. So, to keep this fearfully thin, life-giving gas veneer of the planet ‘clean’ is just simply good husbandry. So how bad is pollution today? The short answer is, that 99% of the atmosphere comprises good clean, largely inert Nitrogen (78%) and live-giving Oxygen (21%) – the other 1% is all other gases and pollutants most of which is harmless hydrogen: the greenhouse gas cocktail (CO2 / Methane / Nitrous Oxide) is less than 0.04% of that 1% comprises 25% Methane, a trace of poisonous nitrates (<0.5%) with a smidgeon of trace gases: most of that 0.04% of the 1% is the harmless human-generated exhaust gas CO2 – rather less than 400 parts per million (or 0.004% – statistically speaking not a significant number). So, in short, the air we breathe (taken overall) appears to be in good shape.

So, what are the environmentalists screaming about? Based on the above, it would appear that they live in a self-inflating bubble, apparently headed in social media by an articulate teenage Jeanne d’Ark battling the Barons of industry knowing little of the messey realities of this world. From within the security of an upper-middle class Nordic family, this environmental heroine rallies her virtual green army of well-meaning lap-top environmentalists – a vociferous media-friendly amateur among hard-bitten but no less shrill professionals – all creating a lot of noise signifying nothing that holds deductive reason. But like during the Covid pandemic, the multi-media cacophony makes it hard for politicians to think straight. That one is an environmental cynic is a function of the apparent self-serving nature of these practitioners. Their cultivation of the concept of ‘Global Warming’ – that element due to mankind’s impact – appears to be more of a carefully nurtured hypothesis, now not so different to a religion – developed by men of faith, stating fiction as fact, and making a good living from it.  

That said, climate change is an indisputable fact: there is absolutely no doubt that planet earth is warming.  It is a singular and undisputed FACT that there is a 100,000-year sun-cycle due to the elliptic path of the planet’s solar orbit. Today we are some 15,000 years into the warming phase after the last Ice Age – the so-called Inter-Glacial period – as the planet slowly gets closer to the sun. This makes it very likely that the principal cause of this planet’s warming is astronomical not chemical. The graphic below on the right shows the change in concentration of CO2 in atmospheric air bubbles over the last million years taken from ice cores in the Artic and Antarctic regions: this is clearly cyclical and sinusoid. The changing concentration is a function of Dalton’s Law of partial pressures. In this, the concentration of the cocktail of gasses that make up the 1% of the atmosphere that is not Nitrogen or Oxygen, increases with temperature – the graphic below is just the CO2 element.

The figures showing the CO2 concentration in the left margin of the graphic appear enormous until you read the small print and see they are parts per million: so that massive spike right at the end on the right-hand side, that is causing such angst in the environmentalist community, represents an increase of 200 parts per million or 0.002% – so don’t panic!!! And, with a 100,000-year spacing on the horizontal axis of this graphic being barely one centimeter, inevitably a 50–100-year timeframe will appear vertical and, possibly (ok, not surely), might be an aberration that would, in such circumstances, disappear when smoothed-out over the 100,000-year cycle.

The Environmental lobby talks in billions of tonnes of CO2 pollution in the atmosphere which sounds terrifyingly impressive, until one realizes that all those billions represent less than 0.004% – a statistical non-entity. And, as explained in the next paragraph, there is surprisingly little science to demonstrate that a trace substance in such a minute quantity (in percentage terms), can have any impact on anything.

That greenhouse gases warm the atmosphere by absorbing Infrared energy is not in dispute – recent experimentation at the Max Plank Institute has clearly shown that, as does the above graphic of the CO2 density cycle. What is more doubtful is the impact of CO2 as an atmospheric trace gas at 0.004%. Making an AI-BOT research on the experimental evidence for this, produced information on observations made with respect to the Pliocene era (3-5 million years ago) when CO2 was at similar or greater concentrations. A further input into the AI-BOT that his was an observation, not experimental, the AI-BOT ‘agreed’ and could only find a single experiment, recently conducted at Harvard in 2015 which showed that even at that low concentration, ‘significant’ quantities of IR radiation are indeed absorbed causing the gaseous mix to warm. The experiment does not appear to have specified or quantified the degree, merely confirming the common experience that in sunny climes, IR radiation warms anything in its path. As to the former observation, with the Pliocene predating mankind altogether, this simply demonstrates the wholly natural character of the increase in CO2 density in the atmosphere that is being experienced right now.

But I disagree: all this is only the background to the argument here, namely the environmental impact of the polluting gases from the efflux of aircraft jet engines. How bad is it?

The graph to the right shows the environmental impact of the whole hydrocarbon sector, now producing some 10 billion tonnes of CO2 pa. Of that, only one third appears to be from ‘engines’ (the blue petroleum line), and of those engines, the few hundred jets touring the globe each day are, but a relatively small element compared to the tens of millions of cars clogging up metropolitan streets around the globe. And if the other two-thirds of hydrocarbon gas and coal elements are also considered – in the main used in the production of ‘clean’ electrical power – the aircraft emissions become even less significant.

Yet, 10 billion is a very large number and in tonnes of anything such is huge but let us put that in perspective. Each of us, through respiration, on average produces about 1kg of CO2 per day. There are now 8 billion of us. So that equates to some 3 billion tonnes of gas each year – almost the same as all the powered motion machinery on the planet, of which the high-profile aviation element is, in truth, only a relatively small part. But, in bowing to multi-media pressure, would the use of SAF in place of Kerosene have any impact on the issue of limiting greenhouse gases or the pragmatics of atmospheric husbandry.?  The short answer is ‘No’.

It is claimed by the environmental clerics (…. sorry, lobbyists) that SAF offers – and here I am quoting BP – an 80% reduction in ‘lifecycle’ carbon emissions as compared to jet fuel (which I reiterate is but a small element of a minute portion of the greenhouse gas problem).  The important word here is “lifecycle”.  Being drawn from the green of pleasant lands and human waste, SAF is still a hydrocarbon so, like kerosene, its exhaust will still flood the atmosphere with CO2, water, and noxious nitrates – that is by the very nature of the natural components from which it originates. It’s just a question of vintage. Those in kerosene are of a several million-year-old vintage – that in SAF is ‘benzene nouveau’. They are essentially the same, the younger vintage perhaps being cleaner and ‘fresher’ (like Beaujolais Nouveau wine, a question of taste if you will) in that, as stated, it is produced from current environmentally friendly vegetation and human waste (admittedly the latter element being particularly good news).

The energy-heavy processes that get SAF from ‘waste to wingtip’ (a great marketing lyric that!) and the associated energy outlay, are similar to those pertaining from ‘crude to kerosene’ (my factual lyric!). So, the science supporting said 80% reduction is likely more related to the math of carbon credit calculations (with electrical production from sustainable sources) than the nature of the polluting chemicals released in the jet efflux from the useful generation of energy from SAF. In short it appears to be little more than a clever, if harmless, ploy to keep the crusading hordes of the environmentalist army at bay until hydrocarbon power sources in aircraft can be replaced with hydrogen and (maybe) electricity. This is reflected in the aviation industry itself in that no serious R&D has been allocated to optimize the production of SAF or its conversion to energy in engines. This is in part evidenced by a recent report in the Air transport Digest (an Aviation Week magazine) that the US government Audit Office (GAO) has discretely recovered some $200m set aside by the Pentagon to assist in the general development of SAF production facilities.

Instead, the industry R&D focus is on the more worthy zero-emission hydrogen and electrical propulsion systems in the next generation aircraft.  And this will happen, likely in a 15-year timeframe. ‘Green’ Hydrogen, electrolyzed from water or other sources, is designated thus because the electricity to extract it, is sourced naturally from Hydro, solar/wind, or geothermal power.  In that, unlike SAF, the fuel efflux comprises only clean water, this will, in an environmental context, truly be a fundamental game-changer and therefore worthy of such focus.  One challenge with hydrogen is its high volatility – storage is mildly challenging but the crash case in the aircraft that it is powering, is more thought-provoking. Counter-intuitively, initial studies show that hydrogen fuel is less dangerous than kerosene. For while very much more volatile, being the lightest of elements (Atomic Weight – 2) it is also very much less dense. Being stored at high pressure, in the event of tank rupture, the massive jet of the gas that will shoot out will always be in the vertical. It has been shown that this vertical sheet of flame, while very hot, immediately dissipates. As such, its impact is very much less than that of a pool of burning viscous liquid fuel typically emanating from the ruptured wing tanks of a conventional aircraft accident – be it kerosene or SAF. For all these reasons, the environmental impact of using SAF in place of kerosene is negligeable while that of ‘green’ Hydrogen will be considerable.

Returning to a more general environmental context, the negative raving in this piece is not to say that climate change should be ignored. Of course not! It is rapidly topping and tailing the planetary ice caps which, whatever else, will raise global sea levels by a meter or more, which is an existential threat to, maybe, a billion people. What has changed in this, our current sun cycle, is that, the last time around, mankind was numbered in millions and, like every other species with which they shared the planet, they were nomadic, hence upwardly mobile.  So, as water levels slowly rose over a few generations in some areas and desertification occurred due to drought in others, all could easily migrate to greener pastures. Today the issue is that, as a function of numbers and our technological advances, the fixtures of our metropolitan civilization and the associated agrarian infrastructure has made us all – man and beast alike – more or less immobile. Hence, faced with the fact of climate change, the emphasis should logically be on protection from its effects rather than futile ‘Canuteian’ attempts at its prevention.

But, given the current latter focus, what can be done to prevent the snail-paced inevitability of this environmental tsunami? Sustainable energy from renewable sources, while largely an irrelevance in this specific context, in the perspective of good husbandry with respect to the thin veneer of the planet’s atmosphere, it is surely worth pursuing. Of more significance is Nuclear Fusion which is now expected to start powering the grid by 2050 thus providing a perfect, sustainable, and unlimited power resource. Taken together, the imminence of these two, deeply green sources of energy, reduces global warming from an existential matter to one of a serious short-term safety issue. Given the imminence of a truly effective fusion solution, like all safety matters, controls and mitigation should meet ALARP (as low as reasonably practical) criteria.  The commercialization of renewables surely meets that criterion: but tinkering with aviation fuels, while a harmless distraction, is essentially a wasted effort and anyway, a total irrelevance.

In passing it is worth highlighting the imminence of fusion power. For more than a generation such has been 10 years away – this may now finally be the case. An outfit in California (Tri Alpha Energy – TAE) expects to have a prototype system capable of producing net electrical power in 2025, with a production prototype in 2035 and OEM supply connected to the grid five years later producing unlimited, (eventually) inexpensive, emission-free (truly green) power source to drive the planet. Such will solve the whole greenhouse gas issue, clean up the planet’s atmospheric veneer and finally put my environmental lobbyist nemeses out of work.

Tinkering with greenhouse gases (should such, at a density of 0.004%, actually be a problem at all!) won’t change that. A measure of the futility of such ventures has been demonstrated by the Shell petroleum company (hence possibly not without some bias) which has shown that carbon capture through current methods of sequestration of the CO2 produced by the hydrocarbon sector alone each year would require some 66 exajoules (that’s 18 zeros!) of energy – or enough to heat/cool all the world’s homes). While such a comparison lacks indisputable clarity, it clearly shows the futility of such politically correct ventures and, unless this associated electrical power is sourced solely from green energy, it will anyway only be exacerbating the problem!