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Climate Change 

April 27, 2009

Population bombs and clocks


Malthus‘ gloomy outlook on the consequences of unchecked population growth has found many champions in recent decades, perhaps most notably Paul Ehrlich. This must be the result of the tremendous growth of both national and global populations in the 20th century. Modern examinations of the consequences take both historical and prophetic tones. Jared Diamond, in Collapse, relates chilling tales of environmental exploitation gone wild in historical societies, such as the Maya, Greenland Norsemen, and the Polynesians of Easter Island. Ehrlich warned us more than 30 years ago (“The Population Bomb“) of the coming collapse of modern societies should population growth remain unchecked. Yet, here we are; we’re still here, and the growth of the global human population is accelerating. Why then should we listen to Malthus and his modern counterparts?

The notion that the human population can continue to grow without limit is simply illogical. As I pointed out in my previous post, non-human populations in nature can never sustain Malthusian growth. So why have we humans seemingly accomplished this over the past few centuries? Are we special? Yes and no. First, let’s take a look at how we’ve manged it.

Modern human society has at least three advantages over its predecessors: increased food production, reduced mortality from disease, and increased security. I suspect that the global population growth rate probably began to accelerate as agriculture was developed in different places, which are historically fairly recent events. More food equates to more people; surpluses support population growth and larger populations. In more recent times, humans have become increasingly efficient at suppressing and reducing mortality due to diseases, especially those caused by infectious agents. The growth of civilized societies (if we choose to define civilized as living in cities) was also often accompanied by increased security and reduced mortality from human aggression. Yes, believe it or not, today we do a far better job of feeding large segments of the global population, controlling epidemics, and keeping ourselves safe from murderous neighbours (both domestic and foreign). Famines no longer sweep through Europe, smallpox has been eradicated in the wild, and wars tend not to last Thirty Years.

Yet one can’t help but get the feeling that things are cracking at the seams. Food shortages have reached crisis levels in many regions. The Black Death probably required several decades to make its initial journey from Asia to Europe in the 14th century, while today we worry about the spread of a global pandemic on a timescale of weeks. And sadly, we now have the capacity to kill thousands daily with conventional warfare, and millions within minutes with weapons of mass destruction. Are these cracks related to population growth? Is the human population reaching a carrying capacity limit? I think that these are very difficult questions to answer, but the answers in my opinion are both yes. There is no shortage of people who are ready to disagree with me, and some of them will point to very clever arguments (all of which I judge to nevertheless be without merit). We’ll explore the questions, arguments and counter-arguments in subsequent posts, as well as the connection to global warming and climate change. In the meantime, check out this very entertaining link.

Filed under: Climate Change — Peter @ 12:25 pm

April 22, 2009

Happy Earth Day

Sung to the tune of Happy Birthday (of course):

Happy Earth Day to you,
May you live in a zoo.
We descended from monkeys,
Bacteria and goo.

Filed under: Climate Change — Peter @ 5:38 am

April 4, 2009

Malthusian musings

Fig. 1 - Example of Malthusian population growth

Thomas Robert Malthus (1766-1834) is perhaps one of the most underappreciated intellectual giants of the 18-19th centuries’ revolution in Western thought. Malthus lived in an age of revolutions; social, political, economic and, of course, scientific. Malthus is best known for his answer to a seemingly simple question (see An Essay on the Principle of Population): Given a particular birth rate, what is the expected growth of a population? Malthus formulated the equally simple answer based on the observation that population growth is multiplicative, i.e. if the average parent organism produces more than one offspring, then the population will grow exponentially over time (Fig. 1). Malthus then made an important leap, pointing out that the Earth, at least in his day, was not overrun by any particular species, and that this was due to resource limitation. Population size is therefore limited by competition among individuals for limited resources. Later on, Malthus’ observations would inspire Charles Darwin’s brilliant formulation of the struggle for existence, and the process of evolution by natural selection. Those observations, along with Darwin’s (who was as gifted an ecologist as he was gifted geologist and father of modern evolutionary biology), also inspired the 20th century fields of population biology and community ecology.

Fig. 2 - Example of logistic population growth

Malthus’s speculation was formulated most powerfully in 1838 with the Verhulst logistic equation, which captures Malthus’ notion of limited resources mathematically. The logistic equation expresses the limitation or slowing down of population growth as population size increases, predicting that size will eventually reach a stable point which is maximally sustainable given available resources (“carrying capacity”) (Fig. 2). In nature, resources may include items such as access to sunlight, water, food, and even sheltered from predators and parasites. The real situation is a bit more complicated, and populations in the wild vary wildly sometimes (see earlier post) but, in general, Malthusian population growth is believed to be absent in nature. Or is it?

Global population growth

The global human population at the start of the 20th century was approximately 2 billion. Imagine this: since Homo sapiens evolved, say 150 thousand years ago, we have gone from perhaps a few dozen individuals, through wars, famine, plague and natural catastrophes, to 2 billion individuals. By the end of the 20th century, in the span of 100 years, the global population increased from 2 to 6 billion humans (Figure 3). It is clear that humans have violated Malthus’ principle. Are our resources unlimited? Hardly. We have continued to be innovative in resource exploitation, and we have also greatly reduced the impact of limiting factors such as predation an disease. Is Malthus now irrelevant as far as humans are concerned? Hardly. The single root cause of all our environmental problems, and many socio-economic and political ones as well, is population growth. The reluctance of many, including environmentalists and champions of good causes, to acknowledge this is nothing short of astounding. Reducing the per capita carbon footprint will be meaningless in the long-term if we have 10-12 billion humans on the planet by the end of this century.

I would like to explore this issue of population growth on the blog. The next several posts will raise some of the questions on my mind, but it is clear that this is a very complicated and sensitive issue. I invite readers to join in the conversation, and to participate with comments and questions of their own.

Filed under: Climate Change — Peter @ 1:39 pm

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