As the name implies, climate zones are areas with distinct climates. They are roughly spread in an east-west direction around the Earth and can be classified using different climatic parameters.
Of course, different areas can have localized climates, with unique distribution and characteristics. Here, we will only look at the major climate zones, the one that form belt-shape areas around the world.
What’s the climate, anyway?
Climate is essentially the average weather conditions in a place over a long period of time — 30 years or more. And as you probably already know, there are lots of different types of climates on Earth.
Typically, the hottest regions are closest to the equator. This happens because the Sun’s light is most directly overhead at the equator. At the poles, light falls at an extreme angle, and only a part of its energy and warmth reaches the ground.
That’s why, in general, climate areas tend to be warmer towards the equator and cooler towards the poles. This varies with lattitude.
How has it changed over time?
Over the past two million years, Earth’s climate continuously changed — usually very slowly. Long, cold periods called ice ages, or glacial, have been interspersed with warmer periods. The last ice age ended about 10,000 years ago. At its height, all of northern Europe and parts of North America, Siberia, New Zealand, Tasmania, and the southernmost tip of South America were covered by ice sheets up to 3,300 ft (1,000 m) thick.
As a result, we are currently living a warm interglacial era that began about 11,000 years ago. We do have some ice at the poles, but it is still fairly warm compared to glacial eras.
These geological changes are common in the Earth’s history, but they are very different from the type of climate change we are observing nowadays. As opposed to a natural change, this is a man-made shift caused by the emission of greenhouse gases. Among the effects of this climate change, warmer areas will expand and move, and ice will melt in the polar areas, raising water levels.
What are the influences on climate?
In the strictest sense, climate is controlled by the energy absorbed and reflected from the Sun, as well as the heat generated inside the Earth through radioactive reactions.
However, considering this energy budget, climate is also controlled by wind, oceans, and mountains. For instance, winds bring moisture from seas to land, producing typically wet climates. North and south of the Equator, the trade winds blow from the northeast and southeast, respectively. These winds converge in the tropics, forcing air to rise. This produces thunderstorms, humidity, and monsoons — characteristics of some climates.
North and south of the trade winds, about 30° from the Equator, there is relatively little wind, and therefore little moisture blowing inland from the oceans. Also, dry air is sinking back to the surface, warming in the process. This is why many of the world’s great desert regions — the Sahara, the Persian Gulf region, and chunks of Mexico — lie at the same latitude. A similar band of deserts lies to the south in Australia, South America, and southern Africa.
Mountains force wind to rise as it crosses over them. This cools the air, causing moisture to condense in clouds and rain. This produces a wet climate on the upwind side of the mountains and an arid “rain shadow” on the downwind side. Oceans provide moisture that fuels rainstorms. They also buffer the temperature of coastal regions, regardless of latitude.
How were the climate zones established?
There’s no clear delimitation, but most scientists agree on a few rough climate areas.
In the early 1900s, climatologist Wladimir Köppen divided the world into five major climate groups. Moist, tropical climates are hot and humid, Köppen wrote. Steppes and deserts are dry, with large temperature variations. Plentiful lakes, rivers, or nearby oceans give humid, mid-latitude climates cool, damp winters, but they have hot, dry summers. Some of these climates are also called the Mediterranean. Continental climates occur in the centers of large continents.
Mountain ranges (or sheer distance) block off sources of moisture, creating dry regions with large seasonal variations in temperature. Much of southern Canada, Russia, and parts of central Asia would fall into this category. Cold, or polar, climates round out Köppen’s list. A sixth region, high elevations, was later added to the classification system.
To this day, Köppen’s general classification endured. Again, this is only a rough demarcation, and should only be considered as a simple climate classification.
What are the features of each zone?
- Equatorial. Lying between the Tropics of Cancer in the northern hemisphere and Capricorn in the south, equatorial climates are home to the world’s rainforests, where rainfall and humidity are high. Surprisingly, temperatures are not that extreme, generally 25-35 °C, and vary little. The hottest months are only two or three degrees warmer than the cooler times of the year. Because these regions are so close to the Equator, the length of day and night hardly varies throughout the year.
- Arid. Our deserts – the hottest, driest and most inhospitable places on Earth – are found mainly across the subtropical continents. Here, descending air forms large, almost permanent areas of high pressure leading to cloud-free skies virtually all year round. Annual rainfall is low and, in some deserts, almost non-existent. No rain has fallen in the Atacama Desert in South America for 400 years. Because they’re so dry, the temperature range in our deserts is huge, regularly exceeding 45 °C by day in summer and often falling to below freezing overnight in winter.
- The Mediterranean. The hot dry summers of the Mediterranean are caused by a seasonal shift of the descending air that also creates our deserts. Low summer rainfall is matched by many months of warm, sunny weather. But, at times, dangerously hot spells of weather engulf the region with fiercely high temperatures of up to 45 °C. In winter, there is more rain and cooler temperatures, but little frost.
- Snow. In the higher northern latitudes, vast areas of the continental interior endure long, hard winters with short, bountiful summers, separated by rapid climatic changes during spring and autumn. The landscape here is contrasting. On one hand, there is one of the world’s largest terrestrial ecosystems – the vast areas of fir and spruce of the Boreal forest. But to the north, where summer temperatures are lower, there is a relatively featureless tundra. Here, the land will not thaw even during the brief summer. Typical summer temperatures are around 15 °C but there could already be frosts by August and ice on lakes by September.
- Polar. The poles experience the coldest temperatures on Earth but the two poles’ climates are different. The Arctic is mostly frozen ocean, while Antarctica is a vast continent of mountains and high plateaus buried under more than 3 km of ice. The Arctic climate is moderated by the relatively warm Atlantic Ocean. Winter temperatures fall to below -60 °C in the coldest regions, while summers range from a few degrees below zero to about 20 °C. Temperatures in the south are colder: winter temperatures often dip below -80 °C. The Antarctic interior is very dry – drier than many deserts. This is because the interior is a long way from the ocean and, as the temperature falls, so does the atmosphere’s capacity to hold the water vapor needed to make snow.
- Temperate. This classification covers a range of climates from near-Mediterranean climates and humid, sub-tropical zones to maritime climates influenced by the oceans – like ours in the UK. The former are mostly found on the western side of continents at 30-45° latitude. Summers can be either hot or warm, but they are always markedly drier than other times of the year. Humid, subtropical climates tend to be in the middle or on the eastern side of continents at 25-45° latitude. Summers here are humid with plenty of rain, but winters are usually dry. Some temperate climates have wet and dry seasons while others have no marked dry season at all. But all have four distinct seasons.
Will climate zones change in the future?
Some scientists believe that Earth will enter another ice age in a few thousand years. However, almost all scientists believe that pollution caused by human activities is slowly causing the planet to grow warmer — a phenomenon called global warming, which can alter the climate zones. The temperature has already increased 1ºC compared to pre-industrial levels, and shows no sign of stopping.