For some reason, after well over thirty years of us all being distinctly in-the-know climate change-wise, lots of people are now working themselves up into a lather over the looming catastrophe we face. Many can be excused for this tardy response as most have been born in the intervening years and are railing against those that did know and chose to do nothing. And rightly so. Why now and not earlier is a bit of a mystery, the facts are not new, but better late than never I suppose. But, what is somewhat unsettling is the fact that some people remain unconvinced that climate change is happening whilst others accept it but try to lay the blame at the door of natural processes or some other convenient get-out clause. Some even think that, although the phenomenon is real, it just isn't as bad as the egg-heads would have us believe and, well, who minds if things are a bit warmer up north? Then there are those that accept it all and yet refuse to change the way they think or behave.
In a way, it is not hard to see why these misplaced, misinformed and just plain wrong attitudes persist as, after all, the planet is a big place and it is easy to develop a mindset that sees humanity’s presence on the our rock as puny and insignificant when compared with the natural forces at work that contribute to the various components of climate. But, of course, anyone that denies climate change or even accepts it but fails to accept its anthropogenic origin is wrong, dead wrong. And here is why in a half dozen landmark pieces of research. This is work that has been published after meticulous inquiry, often over decades, building on many thousands of related pieces of science, and the truth lies within their pages.
Climate is a complex thing, a really complex thing. How it all works is beyond the ken of all but the most specialist of scientists. To say we have to trust them is not an appeal to authority, they are simply to climate what your mechanic is to your car: they are the people who know how climate works and thinking we know better is dumb. Dunning and Kruger Effect dumb.* Understanding how the atmosphere works, how gasses are exchanged between it and the land and sea is a complex business. Then there is the impact of solar cycles on the radiant energy reaching our planet and how much of this energy remains and how much is bounced back into space. Then add positive feed-back loops, changes in the albedo effect, reduced salinity, ocean current shifts as well as half a hundred other factors and bring them all into the equation. It is no surprise that climate scientists employ the services of some of the most powerful computers on earth – there is a lot of maths involved. Climate is so complicated that you quickly come to understand that you simply don’t understand. Thankfully, some people do and it is to them that we must look. Science is a wonderfully self-correcting process and, unlike the blizzard of fakery and “alternative facts” in our modern world, it has an exquisite record in getting to the right answer. Anyone who tells you otherwise is either an idiot, a creationist, or both.
Let’s start way back at the end of the 19th century. By this time the industrial revolution had already spewed out hundreds of millions tonnes of carbon dioxide into the atmosphere over the course of a century or so as the forges and furnaces of Europe and, later, North America, burned coal to make iron, steel and the myriad of other things that an increasingly technological world was demanding. Fortunes were made, dynasties established, squalor abounded and the atmosphere started to change. The famous Swedish physicist Svante Arrhenius published in 1897 a paper that clearly indicated what the implications of altered atmospheric composition would be through showing the effect that CO2 (“carbonic acid” in his terms) and water vapour have on the “transparency” of air to heat.1 The paper is couched in the language of a physicist and, as such, is not an easy or particularly accessible read. One table, does, however, sum it up pretty neatly in a way that we all can understand. That table is here. The smaller the number, the less transmission of heat.
What we have here is a clear demonstration of the fact that adding CO2 and/or water vapour to air very noticeably affects how heat travels through it. The more we have of either molecule (go down for increased CO2, across for higher water) in the atmosphere, the greater the reduction in the passage of heat through it. In other words, heat is retained. The atmosphere acts as a blanket, slowing the passage of heat back into space and the more CO2 or water contained therein, the more insulating the blanket becomes. This is the phenomenon that allows for life on earth to exist and the self same process that makes Venus utterly uninhabitable. Without it the Earth would be too cold for life to exist. It is also the process we are contributing to so perniciously that it is threatening to change our climate irreparably. This paper also discusses, in a way that now seems prescient, some of the likely causes of ice-ages and cold periods, the phenomena much beloved of climate change deniers who probably have never read this, or any other paper for that matter, relevant to the field.
But, demonstrating some very basic principles of how heat and molecules interact is one thing, providing evidence that the activity of man could, in some way, affect the atmosphere to the extent that the climate could be changed is another. After all, with so many vast natural sources of carbon dioxide, how could burning a bit of coal and oil add significantly to it all? This moves us on to 1938 when an Englishman called Guy Stewart Callendar wrote a paper that got to the heart of the issue.2 His paper starts with these words…
And he was as good as his word. This paper goes on to explain the basics of how carbon dioxide absorbs radiated heat at certain wavelengths and how increasing concentrations of the gas will perturb the net outflow of energy from the planet, leading to warming. He described and graphed warming temperatures from a range of locations across the globe over several decades and, most importantly, gave us this graph.
His CO2 units are in parts per 10,000 so multiply by 100 and you get the more familiar ppm (parts per million) values widely-used today. By the time the graph gets to around 400 ppm (4 on the horizontal x axis) we see a rise of about 1°C. We now know that Callendar was extremely close to the mark - not bad for a chap working back in a time where slide-rules were state of the art. Callendar also calculated the mass of CO2 that had been put into the air by man over the half century up to 1938 as 150 billion tons, a massive quantity that now pales by comparison to recent data that shows about 35 billion tonnes annually. He was one of the first to fully appreciate that a small change in the concentration of a gas that comprises a tiny fraction of the atmosphere could have such effects and, ultimately, warm the planet. Interestingly, he saw the rising temperatures that he predicted as being a good thing, increasing crop productivity in northerly climbs and thought that “..the return of deadly glaciers should be delayed indefinitely”.
Callendar’s research is all the more remarkable when one considers it was really done as a hobby, his day job was not as a climatologist but, instead, as a steam and pressure scientist working for the benefit of British turbine manufacturers. Not being part of the in-crowd, many of the great and the good within the scientific establishment of the day dismissed Callendar's work, some but not all. Of those that took note, perhaps one of the most notable is Charles Keeling, and it is to his work in the 1970s that we now move on to.
Keeling realised, as did Callendar, that long term monitoring of CO2 was required. An extremely thorough carbon dioxide monitoring programme was initiated on Mauna Loa in the Hawaiian archipelago.3 The description of how this was accomplished, and the lengths Keeling and his co-workers went to bring precision to measurement and eliminate sources of error, is quite astonishing. As are the results. In common with the other papers cited here, amongst large quantities of data one single chart stands out – the year on year increase in CO2 levels from 1957 to 1972 (see below). Such was the sensitivity of the measurements, even annual fluctuations were detectable that result from seasonal variations in plant uptake etc. The upward trend in the graph gives an unequivocal year-on-year rise in CO2 concentrations of about 1 ppm, concentrations that can only be explained by one thing: human activity or, in more scientific parlance, anthropogenic sources.
Taking measurements on a Hawaiian island meant that volcanic activity was a constant source of error and Keeling and company went to extreme lengths to account for this in their measurements. Their procedures were so sensitive that they even took measures to limit nearby motor traffic as passing cars could produce periodic local elevations of CO2. The work presented by Keeling and his colleagues is extensive, elegant and exquisitely precise and effectively put to bed any doubt that levels of carbon dioxide in the atmosphere were slowly and inexorably rising as a result of human activity.
Despite the building body of data that (a) indicated that atmospheric CO2 was increasing in concentration, (b) this increase was a resulting of human activity and (c) was causing a measurable increase in global temperature, it wasn't until the 1980s that alarm bells really started ringing…
As former Vice President Al Gore noted, climate change is an inconvenient truth that many people cannot seem to look in the eye. Vested interests of various hues just want the issue to go away so business can carry on as normal. Oil, gas, and coal industries all would prefer to carry on as usual, as do some sectors of the aviation industry (think Mr Ryan Air, Michael O’Leary, here), amongst many other commercial activities. The tendency of the political right of many countries to deny, ignore or play-down climate change is a bizarre phenomenon and one that deserves a treatise all of its own. Suffice to say that money is the heart of the issue and such deniers often employ a Rent-A-Scientist or two that are willing to cook up some alternative facts for them. The fact that many people in the west still deny climate change is occurring or, if they don’t, dismiss it as nothing to do with us is a worrying issue, especially when we get one of them in the White House, and is part of an increasing trend for science denial in the west.
Whilst the data is now undeniable and no alternative explanations can stand up to rigorous examination, it is easy to see how some just cannot grasp the simple fact that it is humanity that is causing climate change. When you consider that there is 5.5 quadrillion (5.5 x 1015) tonnes of atmosphere for us to alter, oceans containing around 10 million km2 of water, and huge areas of land for gasses to interact with, how could we possibly be doing all this? Surely other sources of environmental perturbation must be much more important? Volcanic eruptions, for example. Let's take a look at how this natural process adds to atmospheric carbon dioxide and maybe we can understand just what a big deal human-derived CO2 is.
Given that volcanic activity is widespread across the planet and, when a big eruption happens, the images they produce allude to immense forces at work, thinking that all that out-gassing must be important in atmospheric terms is not unreasonable. Not unreasonable, that is, until one does some sums. And here we defer to some people who have sat down and worked it all out so we don’t have to. The go-to publication on this matter is a 2011 review by the American scientist Terry Gerlach.4 It is a short paper and does not contain a user friendly graphic so, instead, I have extracted the data from the paper and made my own. As is readily apparent, emissions from volcanoes are essentially irrelevant when one compares it with CO2 produced by humans. Oh, and please note - the scale is logarithmic so as to make the lower values show up on the graph.
So, as we see, at the very highest estimate, volcanic activity produces around 1.25% of that produced by humans but the more readily accepted figure is 0.8% (based on 0.26 gigatonnes / year). Or, alternatively, our cars and light trucks give off about eleven times as much CO2 as volcanoes based on the accepted value. It is safe to say that, whatever is causing climate change, it ain't volcanoes.
So, as we have alluded to above, humanity pumps out a lot of CO2 annually. But CO2 is not the only player at the table, there are other gasses and they have much more impact when considered on a gram for gram basis. And to find out how much of these other gases is being produced, and how much things have changed over the years, we can turn to a paper by Hoesly et al (2018) where the authors (and there are a lot of them) tot up greenhouse emissions from 1750 up to 2014).5
These two graphs show how dramatic the increase in the outputs of both carbon dioxide and methane has been. The same trend holds true for a range of other gasses that contribute to climate change – nitrous oxide, ammonia, sulphur dioxide to name but a few. The capacity of the sea to absorb CO2 has not changed appreciably, nor has the ability of forests to soak up the gas (if they are left standing, that is). What has changed is the additional quantities of greenhouse gasses that our hard-pressed planet has to deal with. The sources are overwhelming the sinks.
So where is all this carbon dioxide coming from? The above paper also tells us this. Planes, trains, ships and cars, your fridge, TV, freezer and smart speaker, concrete, land-use change and agriculture amongst the hundreds of other things we do, make and use.
It all boils down to our activity and when things start getting worse, there is a tendency for positive feedback loops to establish. The ice-caps shrink leading to less albedo that, in turn, causes less reflection of solar radiation and, hence, more warming. One of the key examples of this is the melting of the permafrost up in high latitudes in a short paper to Nature in 2006 by Katey Walter et al.6
The picture below does not seem much but it illustrates the point of what is going on. The lakes in the tundra of North Siberia are growing as the permafrost melts.
The size of the lakes in 1974 are depicted by the white polygons. As is clear, all the lakes have grown (average = 14% across whole study area) and with this growth comes a release of methane, a gas at least 30 times more potent than CO2 as a greenhouse gas. And much of this methane is old, it has been stored in the ground for thousands of years (35-43,000 in some places). And now, a warming world is releasing this gas at a rapid rate and there is 500 gigatonnes of the stuff stored in the ground up there.
So, there you have it: CO2 begets you a warming atmosphere and this, in turn, causes a cascade of downstream events that may mean we are in really big trouble if we do not stop pumping greenhouse gasses into our atmosphere. The science is complex but the concept is simple. So simple, you would think that even politicians would get it.
*David Dunning and Justin Kruger are psychologists who observed that dumb people have a tendency to overstate their intelligence whereas smart people play down their brain power. A phenomenon most obviously exhibited by the current President of the United States.
1.Arrhenius, S. On the Influence of Carbonic Acid in the Air upon the Temperature of the Ground. The London, Edinburgh and Dublin Philosophical Magazine and Journal of Science 41, 237–276 (1896). https://www.rsc.org/images/Arrhenius1896_tcm18-173546.pdf
2.Callendar, G. S. The artificial production of carbon dioxide and its influence on temperature. Quarterly Journal of the Royal Meteorological Society 64, 223–240 (1938). https://rmets.onlinelibrary.wiley.com/doi/abs/10.1002/qj.49706427503
3. Keeling, C. D. et al. Atmospheric carbon dioxide variations at Mauna Loa Observatory, Hawaii. Tellus 28, 538–551 (1976). https://onlinelibrary.wiley.com/doi/abs/10.1111/j.2153-3490.1976.tb00701.x
4.Gerlach, T. Volcanic versus anthropogenic carbon dioxide. Eos, Transactions American Geophysical Union 92, 201–202 (2011). https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2011EO240001
5.Hoesly, R. M. et al. Historical (1750–2014) anthropogenic emissions of reactive gases and aerosols from the Community Emissions Data System (CEDS). Geoscientific Model Development 11, 369–408 (2018). https://www.geosci-model-dev.net/11/369/2018/gmd-11-369-2018.html
6.Walter, K. M., Zimov, S. A., Chanton, J. P., Verbyla, D. & Chapin, F. S. Methane bubbling from Siberian thaw lakes as a positive feedback to climate warming. Nature 443, 71 (2006). https://www.nature.com/articles/nature05040