In two of the previous climate casebook chapters, we looked at how global population
was distributed across each climate zone, along with the relative sizes of
these zones. Armed with this information, we can now reveal perhaps the one of the
most interesting metrics in human geography in relation to climate – the relationship
between climate and population density – the key index of our planet’s habitability.
Following the episode on population distributions across climate zones,
there were a number of requests to reveal perhaps the most telling of statistics, how climate might
determine the number of people that can be supported in a given unit area. This would
reveal which climate zones are favourable to human settlement, and which ones are adverse. In short,
the respective habitability of each climate zone. So without further ado, I now present the
list of least and most densely populated climate zones on Earth.
At number twelve, it is no surprise to find the Icecap as the least densely populated climate
on our planet. With temperatures constantly below freezing, a continuous covering of ice
and snow prevents any plant growth, with penguins being the only wildlife present
on the desolate continent of Antarctica. With a “population” in the low thousands being all within
the scientific community, these people are concentrated within isolated research stations,
leaving the overwhelming majority of the ice sheet areas of Greenland and
Antarctica being completely uninhabited. At number eleven, and we have the next
warmest zone, that of the frigid tundra wastes, where only a brief cool summer acts as a respite
against otherwise perpetually frozen conditions. Naturally such an inhospitable climate supports a
very low population, comprising mostly of Inuit in the north of Canada and Alaska,
the Sami of northern Norway and Finland, and the Nenets of northern Russia. The other significant
population is split between Chile and Argentina in Tierra del Fuego at the southernmost tip of South
America in what is really a colder form of the Oceanic climate, without the frigid winters of the
Arctic tundra. Spread over such a vast area, this naturally produces a very low population density,
but still orders of magnitude up from the Icecap. Note that the values of this
and the Icecap are inverse – showing the number of square kilometres per person,
and not the usual persons per square kilometre. At number ten, and, once again we progress to the
next warmer zone, that of the Subarctic. Spread over a vast area of North America and Eurasia,
its population is in the millions, so the density is orders of magnitude higher
than the Tundra. Although this figure is deceptive, as the vast majority of these
millions live within the few cities in this zone, leaving most of the endless wilderness
of the boreal forests just that – empty. At number nine, with just over 20 people
per square km, and we increase our population density again by at least an order of magnitude,
with the inhabitants of the Cool Desert regions deep within the northern continents
and on the dry sides of mountains. With arid conditions combined with freezing winters,
it’s no surprise that this is least hospitable climate zone outside of the polar regions of
our planet as measured by population density. Still, the total population does number a third
of a billion, and so these vast regions are home to a significant proportion of Earth’s population.
At number eight and we have the other form of deserts on our planet, those with searing summer
temperatures, but without the freezing winters – the largest of all climate zones – the Hot Desert.
Remarkably, almost a billion people are spread out over the hottest and driest parts of the world,
a testament to the ingenuity of our species. However, as always, average figures can be
deceptive, as most of this population is confined to densely packed areas around rivers such as the
Nile, Indus and Tigris/Euphrates, leaving the vast majority of the desert areas devoid of habitation.
Next on our list, and we go from among the driest to the wettest of all climates,
with the Tropical Rainforest. Only a fraction of the size of the hot deserts,
the rainforests support also a fraction of the population, and so are only marginally
higher in terms of population density. The steamy jungles of the equatorial regions is
not a biome that is suitable for human habitation, being filled with disease,
biting critters and a thick undergrowth that only understands the blade of a machete knife.
Onto number six, now, and we are into our final half, where we find the most densely
populated zones on earth. The first of these is the Continental climate of the interior of the
northern continents, characterised by cold winters but warm to hot summers. The heartlands of the
United States, Canada and Russia are within this large zone, which sports a large population also,
providing a population density double that of the Tropical Rainforest. Unlike the preceding zones,
here the population is not just confined to cities, but also spread out across the vast
plains in the form of farms and market towns as this zone is the first in our
list to be dominated by agriculture. As we move to number five, we increase
the population density again by half, with the Tropical Wet and Dry Climates – the monsoon and
savannah. This is both the second largest and second most populated of all zones, and so is
among the most important planet wide, covering a huge number of countries across the tropics.
Fertile conditions for growing crops such as rice and corn are, however, mitigated by the presence
of tropical diseases, which push this zone down in the list of population density as a result.
Onto number four, now, and the next three zones are the three smallest, starting with the Oceanic
of the maritime continental west coasts. Cool winters and warm summers together with year-round
rain yield the perfect conditions for a rich array of agriculture, but also free from tropical
diseases. Most of the people of this zone are packed within one of the most densely populated
regions on the planet – North-West Europe. With a slightly denser population, at number
three, and we have the Oceanic’s hotter and drier neighbour, the Mediterranean climate zone. With
its unique dry summer conditions, agriculture is more of a challenge than the Oceanic,
but with the right irrigation flourishes under the sunnier days. Perhaps this more desirable
climate has offset any agricultural challenges in giving this zone a more than equal population
density compared to its wetter northern neighbour. At number two and we have the last in the trio
of small climate zones, that of the Subtropical Highlands. Nestled in the uplands of the tropics,
enjoying year round mild temperatures and being free from much of the diseases of the tropics,
it’s no wonder that this zone sports a population density four times that of the Tropical Rainforest
and fifty percent more than the Tropical Wet and Dry climates. Major cities such as Mexico City,
Bogotá, Quito and Addis Ababa are surrounded by fertile farmland where the majority of the
world’s coffee and tea are grown. And so we come to the most densely
populated climate zone of all, and it’s really in a league of its own. It’s the zone with the
largest population, but having a land area only half that of the Tropical Wet and Dry.
It is a climate type that most of you new to this channel would not have heard of but which has now
achieved somewhat of a celebrity status here – it’s the Humid Subtropical of hot summers,
cool winters and plenty of rain. Occupying every eastern continental margin just above the Tropics,
it’s no surprise that this zone, having fifty percent higher density than the next highest zone,
tops out this list, with the enormous populations of China and India packed into relatively small
areas along the Yangtze, Pearl and Ganges Rivers. In these regions the most important of all world
crops, rice, can grow easily. But unlike in other zones where this crop thrives, the cool winters
kill off much of the disease that plagues its more tropical neighbours, improving life expectancy,
and so boosting population density. So with all our zones now calculated,
let’s perform an overall comparison in our final graphic, which is probably the most interesting
and telling in all of the videos I have yet produced. Because in it we can see a clear
relationship of how human habitability is affected by climate. The most densely populated zone,
the Humid Subtropical is two million times greater in density than that of the least,
the Icecap. That’s an enormous leap in orders of magnitude. Most of these orders are consumed
within the polar regions of our planet, however, leaving most climate zones in the
same order of magnitude, from the Cool Desert up. It is clear that a lack of temperature and water
are the enemies of human habitation, with the deserts and polar regions all being at the
bottom. However the effect of cold temperatures is much, much greater than that of aridity,
which is an interesting finding in and of itself, perhaps because technology is able
to arrange for the channelling of water much more easily than the rather impossible task
of warming the air and ground around you. The top four most habitable zones are all
temperate, featuring mild temperatures and sufficient rainfall, escaping the diseases
of the tropics, supporting rich agricultural systems, and generally being pleasant
to human experience. On that very last statement, I know some of you have already made plain your
complaints of the “pleasantness” of the Humid Subtropical, but I bet that if we did a survey,
three out of the top four climate zones listed here would all be in the top of your
lists. You’re all free to share these in the comments, by the way – it’ll be an interesting
exercise in human perception of climate. So that brings to a close the mini-series of
videos about the population and area metrics of climate zones. I hope you found this conclusion
interesting as I’m not aware of this analysis being done in any notable way elsewhere. So
do share this video with your friends or fellow students to impress them with your exclusive find!
Thanks again for watching. I’ll be taking a break from the Climate Casebook for the moment,
as I’ll be launching a brand new series next month. But there will
be more on aspects of climate in the future. To ensure you don’t miss all the excitement,
make sure you’re subscribed to this channel if you aren’t already. Until then, stay green!