Geodiode

The Amazon rainforest, the African Savannah, the sands of the Sahara, the prairies of North America , the forests of Siberia, the ice sheet of Antarctica. It can be easy living in cities, as most of us do, to neglect how much land is on our planet. The continents and islands of our planet cover almost thirty percent of the globe, and most of that fraction is empty wilderness. What determines how these areas look is a combination of topography, and climate. We’ll now focus on the effect that climate has on these areas, and rank each climate zone by size, in this, the latest article in my Climate Casebook.

If you’ve viewed any of my other articles then you should be familiar with the Koppen climate system, which breaks down the world into zones of climate types based on temperature and rainfall patterns. If you haven’t, then I recommend you check out my Secrets of World Climate series, or for a quick overview, the summary article on the Koppen-Geigen Climate Classification.

There are 29 Koppen zones in total, but I’ve grouped most of these into the twelve more distinct categories that formed each chapter in my Secrets of World Climate series. So with that out the way, let’s get right into which climate zones are the smallest and the largest, in ascending order.

At number twelve the smallest of the world’s climate types is the Subtropical Highlands – located in the tropics, but experiencing mild temperatures year round thanks to the cooling effect of altitude. These areas are distributed relatively equally across Latin America, Africa and around the Himalayas in Asia. The monsoon variety of this climate, featuring wet and dry seasons dominates over the year-round variant, with the higher altitude cool summer variant extremely rare.

At number eleven, we have the next largest zone – that of the Oceanic – the mild, wet climate found on the west coasts of the continents at temperate latitudes. Most of the land area is found in North-West Europe, with a significant proportion in Oceania. The main variant of warm summers dominates, with the cool summer Subpolar variant restrict to rocky coasts in the far north and south.

At number ten, we have the Oceanic’s southern neighbour, the Mediterranean climate of dry summers along the west coasts of the temperate latitudes. The country with the largest single land area here is, interestingly the United States, whose long west coast is almost exclusively of this type. Australia and Chile have some areas here, but the vast majority is given over to the countries around the sea to which this climate owes its name. The relative land areas of the hot and warm variants of this climate are pretty even, with Csa being slightly more widespread.

The next largest climate type, at number nine, is the Tropical Rainforest, covering selected parts of the equatorial regions of our planet where rain is constant year round. Almost half of this area is within Brazil and Indonesia, with the remaining countries scattered across South America, Africa and SE Asia.

Moving onto number eight now, and we switch to the opposite end of the Earth and opposite temperatures, with the frigid wastes of the Tundra. Most of this land is in the Arctic, with over half of it in just two countries – Russia and Canada. You might be wondering what China’s contribution is all about here – well that’s the extensive Tibetan plateau, which, being at an altitude of over 20,000 feet is predominantly alpine tundra. The United States fraction is almost all from one state – Alaska.

Onto number seven in our climate land areas list, and we have the climate zone that has the largest population of any other, the Humid Subtropical of hot summers and cool winters mixed with plenty of rain, occurring on the eastern fringes of each continent. Almost half of the global land area of this type occurs in just two countries, the United States and China, with the rest scattered across other continents. The year-round rain variant is the larger of the two, with the smaller being the monsoon form with dry winters.

Into the final six now and we have the Continental climate types, which stretch across the vast plains of North America and Eurasia at the mid latitudes, characterised by warm to hot summers and cold winters, but with adequate rain to support large populations. This climate type forms the heartlands of three countries – Russia, the United States and Canada, which together make up over half of all global area for this climate. China’s densely populated north-eastern part features also – with the remainder being in Eastern Europe and NE Asia. There are many subtypes to this climate, varying by summer temperatures, and annual rainfall distribution. A single type dominates, that with year round precipitation – rain in summer, snow in winter, together with a warm summer.

The fifth largest climate zone is the Cool Desert, stretching across the rain-starved continental interiors, where large temperature ranges in combination make for a tough existence. Most of this area is covered by the countries of Central Asia – with most of western China in this category. Similarly, most of the western half of the United States is comprised of this climate zone. The remainder are scattered across the other continents. The true desert and semi-arid forms of this climate are equally matched in prevalence.

Onto number four, and no it has not been forgotten, it’s the most forbidding of all climate zones – the Icecap. Almost the entirety of the large continent of Antarctica is covered in ice year round, and this continent alone makes up the vast majority of the land area of this climate type, with the remainder being in Greenland, and a comparatively tiny scrap as glaciers across the highest mountains in the rest of Earth.

As we move to number three, and we have the climate zone with the next coldest winters, the vast boreal forests of the Subarctic that cover twelve percent of the entire land area of earth. Dominating the northern continental interiors of North America and Eurasia, it is no surprise that two countries make up the vast majority of this land area – Russia and Canada. The variant with cold winters and year-round precipitation dominates this climate type, with monsoon and very cold winter forms comparatively isolated.

Onto number two in our climate land areas list, and we are back in the tropics with the wet and dry seasonal climates – the Tropical Monsoon and Savannah. These lands dominate the tropics, making up almost 75% of land area in this region of earth, with the Tropical Rainforest making up most of the remainder. Although the vast savannah of Brazil makes up almost a quarter of this climate’s land area, the remainder is distributed across very large number of countries across Central and South America, Africa and SE Asia. The Savannah variant of more pronounced dry seasons dominates over the wetter Monsoon form.

And so we come to the world’s largest climate zone. By a process of elimination you might have guessed what it is. And it’s a fact that might bring you some concern, with all the talk of climate change. Because the most extensive climate regions on Earth are the Hot Deserts. Making up a full fifth of all continental areas, the Sahara itself being half of it, the scorching arid lands of the subtropical regions of our planet can appear deceptively smaller than the subarctic regions on a map because of the errors in projection that cause more polar regions to appear larger. When looking at the distribution of these lands, it’s not surprising to find the countries adjoining the Sahara dominating, although the single largest contributor is the land down under, whose continental bulk is made up predominantly of desert. The true hot desert dominates over its slightly wetter semi-arid form as this chart shows.

So, with our list complete, let’s now make a comparison of our twelve grouped zones, in our final graphic. There are two notable patterns here. The first is that almost half of the land on earth is practically unusable by humans, in the form of arid desert, ice-sheets or tundra. The second is that the three smallest zones combined are barely bigger than the next largest, and yet these zones contribute enormously to global agriculture, from the fruits of the Mediterranean and the cattle of the Oceanic, to the corn of the highlands of Central and South America. So if you’re from one of these regions, like I am, don’t feel bad. Remember, small is beautiful!