The Bacterial Growth Curve & Petri Dish Earth

In 1993 when I was a first year biology student I first became aware of what is known as the bacterial growth curve. It is a cornerstone theory of microbiology, one that every microbiology student learns probably on their first day. Best described by a simple graph (see figure below) it describes the population trend of bacteria in an enclosed petri dish, with a finite food source (in the form of fortified agar) at constant temperature, and no inputs from exterior environments post inoculation, i.e. nothing further is added to the petri dish once the bacteria of choice are introduced.

Standard Bacterial Growth Curve

There are 4 principle stages. 1) The lag phase; 2) The log phase (or exponential phase); 3) The stationary phase; 4) The death phase.

Stage 1, the lag phase occurs from point of introduction (inoculation). This is where the bacterial cells acclimatise to their new environment. Little or no growth occurs at this stage, although the cells may increase in size as they feed on abundant nutrients under optimal environmental conditions.

Stage 2, the log phase is characterised by an explosion of bacterial population numbers. For the bacteria, these are the boom times. Enriched by an abundance of nutrients and moisture, optimum temperatures, minimum or no competition, and low levels of bacterial waste, the bacteria divide and double their population numbers every generation time (which can be short as 20 minutes for some bacteria species).

Stage 3, the stationary phase. At this point the bacterial population growth rates begin to level out. The number of bacteria dividing and reproducing is balanced by the amount of dying bacteria from the depletion of nutrients and moisture and an accumulation of bacterial waste products.

Stage 4, the death, or decline, phase. Here without additional resources introduced to the bacterial environment, the population plummets as the death rate exceeds the reproductive rate. Left alone in an incubator over a long enough time period, the population completely dies out, with the exception of bacteria that can form spores. The formation of spores are a different story, which I won’t go into.

Now allow me to make a giant imaginative leap. To me, the petri dish in this theory can be extrapolated to be earth. Obviously, the planet and a petri dish are light years apart in levels of complexity, yet despite all our technology (many argue because of our technology) humans are experiencing a similar trajectory as those of bacteria in a standard growth curve. In petri dish-earth we are the bacteria, and the earth’s resources are the agar. We are self-contained, there is no more food or water or houses or farms or land coming in from space. We are, when we think of it, in the final stages of our log phase, stage 2.

I put it like this, because it is the simplest way to think about the problems the planet now faces. Skeptics can argue that a petri dish bears no resemblance to planet earth, and that bacteria pose no comparisons to humans because we have technology and medicine, and so forth. Indeed we do, but such skills are merely our limited skills and nothing else. There will be a point where they no longer mitigate against the inevitable ceiling of human ingenuity, beyond which who knows what. Indeed, it has been argued that we are at the end of discovery (ref), and that the rate of scientific and industrial advancement has been slowing for quite a while. That reference just given is framed in the context of US technological advancement, not the planets as a whole, nevertheless the debate on that one is lively.

I have been thinking about this because I just read media reports about an MIT computer prediction from back in 1973, the year I was born. 46 years ago. (Link). It calculated predictions on the likelihood of the survival of human civilisation on its then perceived course of predicted pollution levels, population growth, limits of resources, and the quality of life on earth. The work came to notice again last year when Australian media did a piece on it on the basis that its predictions were eerily accurate and appear to be coming to pass.

And in fact, this is quite true. I only have a problem with the element of surprise that has come with the reactions to its predictions. If one is familiar with the bacterial growth curve, and if one understands such simplistic concepts as finite resources and waste accumulation then maybe we should not be so surprised. After all, if we use everything up, there is nothing left. And what happens then? Usually when we need resources we invade other countries. But what happens when we have used up that avenue as well? Well we can maybe travel to other planets or moons eventually and save ourselves, which is what some “visionaries” are postulating (link). The problem here is that there is nothing seemly even remotely habitable close enough for us to travel to. The technology required to identify suitable locations (that are likely light years away) and travel to them is decades away from existence at the very least, if we can develop it at all. In any case, we don’t have that timeframe, according to the MIT studies from 1973.

When is it lights out for humans according to the report? Our civilisation will have collapsed by 2040. And our quality of life is set to dramatically drop after 2020. I am writing this in early December 2019. Oh dear!

Admittedly, it is very easy to dismiss this prediction. After all, I am writing this blog post in a comfortable library in Dublin City centre, and there is not panic. The air here is clean. I have enough food, warmth, I am not sick, and there are no dangerous storms raging outside (there is though, a drunk library user beside me who is making me ill at ease. It is 3pm in the afternoon). And after all, it was only a computer prediction.

Except it wasn’t. The recent media reports on the work concentrate on the computer side of things, but in fact it was a highly detailed report on a multifaceted sociological scientific study, that employed state of the art (for its time) computers. It was actually part of a larger sociological research project on population collapse and it is considered ground-breaking work in its field. A worry I have is that the media reports focusing solely on the computer simulation aspect of the work makes it easier to be dismissed by climate crisis deniers.

But, let’s look at publications that are more than a prediction, and instead are recent reviews of hard scientific data. Here is one that came out in June this year (2019) pretty much saying the same thing (link). The International Panel on Climate Change has published lots of them, some of which I wrote about here (link). To pick a random recent scientific report on climate warnings, here is a scary one (link). This one was published last week. It suggests that we may have already passed some very serious and irreversible tipping points in the climate crisis. A tipping point is what it sounds like – a point of no return. In science, particularly in the climate sciences, the processes (atmospheric, chemical, biological, meteorological, to list a few) are inextricably interlinked making it virtually impossible to understand any one process as a stand-alone entity. So, if a complex series of climate related events have come to pass, after which we have no mitigating technology or recourse, we are, in effect, in big trouble. It means the process has run away with itself. And these predictions and warnings which are being sounded now in 2019, and prior, are coming at around the time when the MIT computer simulations from 1973 predicted. Our giant petri dish earth is emerging from our population boom time (our exponential growth phase) and entering our stationary phase where our growth rate will slow and balance out, and our numbers will begin to reduce. That sounds like a good thing for the planet, which is what we want, except when you realise it means a correction of our population numbers, which are currently in the billions (ref). This is a piece of stark information which I notice most media coverage of climate warnings fail to explicitly spell out. Simply put, we need to act now, or we die. If this sounds like alarmist liberal propaganda, it might be. I am a liberal I guess (within the American context anyway), and I am writing about something which I think is extremely important. But it is also true.

And that’s the point here: just google the phrase “climate change” and watch the bad news stories pile up in your browser. Australia, the Amazon and Siberia are burning; the glaciers in Greenland, Antarctica and the Arctic are melting pushing us closer to ice collapse; the cities of India, China, Indonesia and South East Asia are choking with air pollution; coral reefs are bleaching and dying the world over from a multifaceted range of threats; permafrost in Siberia and elsewhere is thawing; and the Atlantic Circulation (an immense circulatory ocean current that plays a key role in regulating climate) is weakening. In fact, reports state that it is at its weakest in 1600 years (link). Other reports state that CO2 has not been seen at such concentrations in the atmosphere since the Pleiocene around 3 million years ago (link). Others suggest if we continue business as usual carbon emissions are heading levels last seen 50 million years ago (link).

All something to think about as voters go to the polls.

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