Our atmosphere plays a major role in regulating our planet’s climate.

It maintains a complex mix of greenhouse gases that keeps our planet from getting too hot or too cold. It also helps control the amount of water vapor in the environment that’s essential for our survival. 

But less apparent is our atmosphere’s role in influencing the strength and direction of wind patterns. Atmospheric circulation, as it’s called, drives our weather and creates the climates of our planet as we know it. In this article, we explain what drives atmospheric circulation and how it affects climate change.

What is atmospheric circulation? 

Atmospheric circulation refers to the consistent pattern of airflow around our planet’s atmosphere. It occurs mainly in the troposphere, which is the region of the atmosphere that extends 8 to 14.5 kilometers above the Earth’s surface and where almost all weather events form.

Atmospheric circulation is an essential part of Earth’s climate system because it redistributes heat around the planet. These large-scale wind circulations move in response to differences in temperature at the equator, the warmest region of the planet, and the poles, which are the coldest regions. 

They carry heat from tropical regions to polar regions to keep them inhabitable. They prevent areas around the equator from becoming hotter and polar regions from becoming colder. 

Without atmospheric circulation, the weather on our planet would stop. Clouds would not form as there would be no air flowing over oceans to collect moisture. Over time, plants and animals would begin to die from the lack of water. 

What causes atmospheric circulation?

Atmospheric circulation is caused by two major forces: solar radiation and the spin of the Earth. 

Energy from the sun passes through our atmosphere and gets absorbed by the landmasses and oceans of our planet. This causes the surface temperatures of land and water to rise, which in turn creates masses of hot air to form above them. But because the Earth is tilted, curved, and covered with snow and ice in some areas, various parts of the world heat up at different temperatures.

The resulting temperature differences create a phenomenon known as convection, where cooler air from higher up in the atmosphere sinks because it’s denser and gets replaced by the rising warm air. 

Convection happens in every region of the planet but is mostly driven by air circulation patterns at the equator, which is the hottest region of the Earth. When the hot air at the equator rises to the edge of the troposphere, it starts to travel to the north and south poles. But because Earth is spinning, the traveling air turns per the spin of the Earth. 

This effect, known as the Coriolis Effect, makes atmospheric circulation dynamic. The constant meeting of moving hot and cold air masses produces three large, and distinct,  convection cells north of the equator and three south of the equator. These cells move almost separately from one another and give us different weather conditions.

What are the three atmospheric circulation cells?

The three atmospheric circulation cells created by the Coriolis Effect are the Hadley, Ferrel, and Polar cells. Although the cells occur separately at different latitudes, the hot air masses passing through them are the same, therefore connecting each cell.

Here’s a look at how each cell affects our planet.

Hadley cell

The Hadley cell is the atmospheric circulation cell closest to the equator. It forms when hot air rises at the equator and cools and sinks toward the ground at 30 degrees north and south. With the Earth’s spin, the winds are deflected to the right in the northern hemisphere and to the left in the southern hemisphere. Ships rely on these ‘trade winds’ to navigate around the world. 

When the hot air sinks, it becomes warmer and drier. The resulting air creates the low-moisture, almost cloudless, climate that’s found in desert regions.

Ferrel cell

The Ferrel cell occurs at higher latitudes between 30 degrees and 60 degrees north and 30 degrees and 60 degrees south. The winds that travel within this cell carry warm air from the tropics toward the cold air drifting down from the polar regions. Most of the air that circulates here is heavy in moisture and creates unstable weather conditions associated with the mid-latitude depressions.

As the air in the Ferrel cell is pulled towards the poles, it forms the south-westerly winds in the northern hemisphere and the north-westerly winds in the southern hemisphere.

Polar cell

The Polar cell lies between 50 degrees to 60 degrees north and 50 degrees to 60 degrees south. The winds that travel within this cell flow from east to west, earning them the nickname ‘polar easterlies’

In this region, cold polar air mixes with the warmer tropical air and creates a zone of low pressure called the subpolar low. The weather here is often very unstable with extensive cloud cover. 

How does atmospheric circulation affect the climate? 

Atmospheric circulation creates winds that distribute heat and moisture across the surface of the planet. Together with surface ocean currents, it carries moisture from the oceans over large swathes of land. 

These winds affect the water cycle, including the amount of rainfall each region receives and the frequency of storms. Over centuries, the distinct weather patterns formed by the level of moisture in a certain area become our regional climates. 

It’s the main reason why we have areas of high rainfall, like the Amazon rainforest, and areas of dry air, like the Sahara desert. In the Hadley cell, for example, hot air is swept to the north and south of the equator. As the hot, dry air descends, it absorbs moisture from the soil and leaves the soil parched, creating the desert-like conditions found at 30 degrees north and south latitude.

For now, the link between atmospheric circulation and our climate remains an area of intense research. The rapid changes in our climate have led some climate scientists to wonder if atmospheric circulation might play a role in the warming of our climate. 

Various studies conducted in recent decades suggest that atmospheric circulation may bring warm air from the oceans into high latitude countries such as those in Eastern Europe during the winter months. 

How atmospheric circulation spreads pollution 

Although the relationship between atmospheric circulation and air pollution is still being studied, there is increasing evidence that pollution can be carried thousands of miles by air currents. The strong winds created by atmospheric circulation are believed to have the ability to carry air pollution from one region of the planet to another.

In Asia, for example, clouds of industrial pollutants are picked up by eastward air currents in China and deposited across Japan and the Korean peninsula. Similarly in the US, sulfur dioxide from coal-burning was carried from the Midwest into Canada in a matter of weeks. 

There’s now evidence that even smog from China and India has drifted across the Pacific Ocean into the western US over the past 25 years. The National Oceanic and Atmospheric Administration (NOAA) found that Asian air pollution caused a 65 percent increase in ozone levels in Yellowstone, Yosemite, and 14 other western US national parks. 

What can we do to limit the effects of climate change?

Climate change is occurring at faster-than-normal rates due to increased human activity. We are flying more, consuming more, and taking less care of the environment - all of which contribute to a rise in atmospheric greenhouse gas levels.

To limit the effects of climate change, we need to make changes in the way we live and travel. Here are three things that we can do collectively to slow down climate change.

Use active modes of transport 

Using active modes of transport like walking or cycling can help reduce traffic-related air pollution. It’s believed that roughly one-third of America’s carbon emissions come from the use of cars and trucks to move people and goods. 

If we can reduce our reliance on fossil fuels for transport, we could make a significant dent in the amount of planet-warming carbon dioxide and fine particulate matter (PM2.5) that gets emitted into the atmosphere. 

Switch to renewable energy sources

Switching to renewable energy sources like solar, wind, and geothermal energy can also help us reduce our reliance on fossil fuels. These clean energy systems can be installed as part of microgrids or on individual properties and supply electricity to homes and businesses without needing to be linked up to a coal-powered electricity grid. 

Consume food from a sustainable source

A study in 2021 found that bottom trawling for fish and other kinds of seafood releases millions of metric tons of carbon trapped on the ocean floor, endangering marine life and limiting the ocean’s ability to absorb atmospheric carbon. 

The findings recommend that people eat seafood caught using sustainable methods such as rod-and-reel fishing and cast-net fishing.

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