Let's change the model a little bit
to make it a little bit more consistent,
with what I spoke about in the last lecture.
Instead of an arithmetic growth level,
let's move back to that carrying capacity idea.
Remember how the reindeer could only grow past
this carrying capacity for
a certain amount of time for crashing back to Earth?
We'll explore this idea in more detail later,
but for now think of it as an idea of
how much population could be supported.
Usually food is the limit,
as in the case of reindeer.
Other natural limits could be pollution,
energy, water, space to live.
In this case, there would be
a flat line as shown by the green line in the figure.
Now, we reach a point of crisis and population crashes,
and this time, we're kept to
that straight level that carrying capacity.
Note that doubling the food supply,
so if we have a new technology,
a new green revolution,
and new ability to create food,
merely delays the inevitable.
In the world's case, if we're
growing at one percent, per year,
if we have a new ability,
a new technology, to double the food supply available.
All we do is postpone this crash into
subsistence misery by 70 years.
As you can see in this graph,
all we do is delay the inevitable,
because we shift up the carrying capacity,
we double the carrying capacity of the Earth,
but because at current growth rates,
we're going to have double the population in 70 years.
Then all we've done is bought
70 years more time before
we reach this catastrophe point,
where we're all on the edge of starvation.
This inevitably comes from
the exponential growth in population.
So if population is always exponential,
like in that reindeer case until the crash,
then we're always destined
to hit this wall of starvation.
It's even more depressing,
If you think that we've gone
beyond the carrying capacity.
So for example you might say that modern agriculture
is too dependent on fossil fuels,
and since fossil fuels will eventually run out,
then we're artificially living
above our carrying capacity.
So we can imagine then,
that if we have
a population that lives above the carrying capacity,
according to the Malthusian model,
we are destined for a crash.
So in other words, the population will collapse.
Of course, a population collapse of
a large magnitude would
probably collapse society as well.
Could civilization survive, if we
only had half enough food to go around.
There are lots of things that could
follow this pattern beyond population.
Of course, we might think about
mined goods including energy, like fossil fuels,
but also essential resources,
or some would say well that we're
mining top soils in modern agriculture.
So you can use this sort of Malthusian model,
not just for population but for lots of
other potentially unsustainable systems.
Now it turns out,
that we did not have the sort of collapse that
Malthus predicted over the last 200 years.
But in defense of Malthus,
his model was essentially
correct up until the point of time in which he wrote it.
This is an image of
urban poverty in 18th century Britain.
At this point in time,
the masses of Britain were very poor.
The increases in agricultural productivity
seen over the last couple of centuries in Britain,
had done very little to alleviate this poverty because
population growth had indeed
matched this increase in
the carrying capacity of the country.
In fact, it's been argued that
living standards in 18th century Britain,
that is for the average person living in the country,
were lower than they were for
the stone age peoples that they replaced.
The stone age peoples were much less numerous.
They were far less people,
but they actually had more calories,
and they had more protein, and they had more meat.
So it has been argued that being a median person,
that is the middle person in
18th century Britain meant that you had a worse life,
than you would if you were
a Stone Age hunter and the gatherer.
So Malthus's model was
a very good description of what had happened,
over the past few thousand years in Britain.
In fact, the only times that
the average Britain was better off,
was when there was a catastrophe from other reasons.
So for example, when there was the Black Death,
about a third of
all the people on the island were killed,
and this suddenly meant that there
was much more land available,
and so the demand for labor went up,
and at that point in time,
the average peasant farmer
enjoyed a higher standard of
living than they did previously,
or afterwards once the population
came back up to that carrying capacity level.
This is all very consistent with a Malthusian worldview.
So we should remember that,
when we're thinking about this model.
The reason why I bring this up is because otherwise,
Malthus made a spectacularly
wrong prediction about the future.
This is England's population.
The blue line represents the population change over time,
and the yellow dot is when Malthus published his model.
As you can see, what happened
directly after Malthus published the model,
was that there was an enormous increase
in the population of England,
the more the population doubled,
then doubled once more,
and has almost doubled again,
in the last 200 years.
Not only that, the average Britain is far
wealthier today than they were 200 years ago.
The Industrial Revolution meant,
that the average person in the country has
about 15 times as much wealth
today as they did 200 years ago,
when Malthus wrote his predictions.
So rising populations has not led to mass starvation.
Not only that, rising populations
has not made people poorer.
In fact in both of these cases,
the reverse has happened.
People in Britain are more numerous and wealthier,
than they were 200 years ago.
People make Malthusian predictions today.
This is often called Neo-Malthusian,
it's new Malthusian prediction.
Recent Neo-Malthusian predictions have been as
bad as the predictions made by Malthus 200 years ago.
For example, Paul Ehrlich,
wrote in 1967 that the battle to feed all of
humanity is over in the 1970's and 1980's,
hundreds of millions of people will starve to death,
in spite of any crash programs embarked upon now.
Now, this statement was made in 1967,
and I've marked this with a yellow dot on this graph.
The blue line is the world population since then,
the population has doubled since the prediction was made,
as has the world income per person.
So people are both wealthier and more
numerous than they were when this prediction was made.
As you can see the very opposite of what a
Malthusian would predict has happened across the world.
This thinking may indirectly influence a lot
of other sorts of documents we
read when we think about sustainability.
This is from one of the very early texts
that considered sustainability issues,
it's for the Agenda 21 document
from the Rio Earth Summit.
Baye suggested in this document than
a less significant changes were made to
the world economy and social systems.
This was in 1992, we can expect to
have the same sorts of issues Baye talked about,
perpetuation of disparities between nations,
or worsening of poverty,
more hunger, ill health, and literacy.
Now on all of these measures,
the reverse has happened.
Globally, there's more wealth,
there's less illiteracy, there's better health.
So we have to be aware that when we hear about
these Malthusian predictions that it is following
a model that sometimes works, and sometimes doesn't.
Now it is possible that we are living on borrowed time,
and that the only reason why
these predictions have failed,
these more recent predictions,
is because they're just a little bit too early.
Maybe we're living on unsustainable practices,
just like the reindeer were for so many years.
Surely there must be some limit
to how much population growth we can have.
I think that's probably true,
but in the next set of lectures,
we're going to talk about population growth,
and we're going to find out
that it's not all doom and gloom.
