Earth’s oceans are vast, covering over 70% of Earth’s surface. Oceans play a major role in climate by dominating Earth’s energy and water cycles. Ocean surface currents are the energy transport mechanisms. It helps to drive and maintain many of Earth’s climate zones. Do oceans warm up and cool down? Like the atmosphere’s temperature, the Ocean’s surface temperature is constantly changing.
The oceans are a major and active component of the climate system, absorbing about twice as much sun’s radiation as the atmosphere or the land surface. They absorb, store and move heat, delivering vast heat energy to the global climate system.
What are ocean currents?
Streams of water move along the surface of the ocean in definite paths. Ocean currents are called more or less permanent streams flowing in a definite direction from one part of the ocean to the other.
- Ocean currents can be thousands of kilometers in length and sometimes about 200 kilometers wide.
The ocean surface currents function to move large amounts of heat across the planet globally, redistributing heat and water vapor. Surface winds typically drive ocean surface currents. Also, it can have a huge impact on climate.
For example, Northwest Europe, despite its latitude, is not a frozen land because the Gulf Stream off the eastern coast of the United States transports warm water north to those areas.
In the Pacific Ocean, the Pacific North equatorial and the Pacific South Equatorial currents driven by the trade winds move heat from North and South America’s west coast to Japan. These ocean current loops keep heated water moving into colder regions and return cooler water to the tropics. There’s a connection between plate tectonics, ocean currents, and the climate.
How do ocean currents affect climate?
Ocean currents originate in the equatorial regions as the warm equatorial currents and flow westward. When they encounter continents, they divide into two branches. One is deflected in northwards and the other southwards. These warm currents move along the East Coast in the low and middle latitudes.
As these currents reach the higher latitudes, they move across the ocean. They turn towards the equator washing the Western margins of continents. But this time, the warm current loses much of its warmth. It flows along the west coast as a cool current. Finally, the current will warm when it reaches the equator. Also, it becomes a part of the equatorial current.
The currents of the Indian Ocean differ from those of the Atlantic and the Pacific Oceans. It is mainly because of the enclosed nature of the sea and the influence of the monsoon winds. Also, In the northern part of the Indian Ocean, the direction of the current changes according to the season.
- When the southwest monsoon blows in summer, the current flows in the western direction.
- In winter, when the northeast monsoon winds blow, the current flows in the eastern direction.
The currents in the southern part of the Indian Ocean are similar to those in the southern parts of the Atlantic and Pacific Oceans.
Climate is best defined as the general atmospheric conditions over a place over a minimum of 30 years or more. The five factors that affect climate are:
- Latitude or distance from the equator.
- Ocean currents.
- Distance from the ocean or continentality.
- Altitude is also known as height above sea level.
- Relief or the shape of the land.
Ocean currents are giant underwater rivers or conveyor belts of water flowing in the oceans. Many contributing factors create these ocean currents. Some of these include the winds, Earth’s rotation, the water temperature, and the water’s salinity or salt content.
There are two categories of ocean currents: Warm currents and Cold currents.
- Warm ocean currents originate at the equator. They warm transport water south and north to the high latitude.
- Cold ocean currents originate at the high latitudes and transport cold water toward the equator.
Ocean currents are generally named after the regions along which they flow. The warm ocean current flowing along the Brazilian coast is called the Brazilian current. Moreover, the cold current flowing along the Labrador coast is known as the Labrador Current. The wind system of the world powers ocean currents. The wind systems of the world post the surface water of the oceans to move in a particular direction.
What do ocean currents have to do with climate? Cycling water by ocean currents produces climates in different parts of the world. Let’s look at the effects of ocean currents by examining their effect on the coastlines of countries or regions.
The southern African area is situated on Southern Africa’s east coast in the Indian Ocean. Along the west coast, you can find the South Atlantic Ocean. Both of these oceans have a massive impact on the climate of southern Africa.
- In the northern hemisphere, the currents move clockwise. In the southern hemisphere, they move counterclockwise.
The current flowing through the section of the Indian Ocean that borders southern Africa is the warm Agulhas current. This current moderates the East Coast temperatures by providing a constant flow of warm water from the equator. It leads to lots of evaporation occurring off this current. As a result, places along the east coast, like Durban, have humid summers with lots of rainfall. Southern Africa’s East Coast also has a lot of green vegetation.
The current flowing in the South Atlantic Ocean is the cold Benguela current. This current brings cold water from the South Pole. Due to the water’s cold temperatures, very little evaporation occurs along this coastline. The climate is arid throughout entire Europe.
The Namib Desert dominates the west coast of southern Africa. It is widely thought to be the oldest desert globally, and estimates put its age at around 55 million years old. It is also one of the driest deserts in the world, and very few people inhabit it. The west coast of South America is also dominated by a desert called the Atacama Desert. The west coast of North America contains the Sonoran Desert.
Another example of the effect of ocean surface currents on climate is the Hawaiian Islands. Here the weather is cooler than usual for a tropical latitude. It is due to the cooling effect of the California Current returning from the north equatorial current, which runs north from Asia. The California Current produces San Francisco’s temperate climate and characteristic coastal fog on the west coast of North America.
What causes ocean currents & climate change?
The prevailing winds lend speed and direction to a mass of water. Ocean currents in the northern hemisphere deflect to the right of the wind direction. Currents in the southern hemisphere deflect to the left. Therefore there is a clockwise circulation of water in the northern hemisphere and an anti-clockwise circulation in the southern hemisphere.
This is a Coriolis effect caused due to the rotation of the earth. The surface motion of prevailing winds drives the subsurface layer at an angle. Each layer moves at a slower speed than the one above it. The spiral was created as the overall effect of moving the water mass above the depth of frictional resistance. It is an angle of 900 from the wind direction. It is called a Coriolis effect.
- The temperatures are higher at the equator than at the poles. Hence water in the oceans near the equatorial regions gets heated more than in the oceans near the poles. This unequal heating sets up conventional currents in the sea.
The warm waters of the equatorial regions are light. They move along the surface towards the cool polar regions. The cold water is dense and heavy. It sinks downwards from the surface and moves slowly towards the equator, where on warming up, it rises to the surface again.
Salinity is another factor that is responsible for ocean currents. Salinity is affected by freshwater inflow from rivers melting ice, rainfall, and evaporation. A current of normal salinity flows in, and a deeper water current carries out a higher salinity.
For example, a high evaporation rate in the Mediterranean Sea increases the salinity and the water’s density. As a result, less dense saltwater flows into the Mediterranean from the Atlantic and the Black Sea. In comparison, smaller currents of higher salinity flow outwards beneath these currents. The salt content of the basin remains constant.
Other factors affecting currents are the configuration of the ocean bed and the shapes of landmasses. For example, the not equatorial current flows towards the West Indies in the Atlantic Ocean. The most current is channeled into the Gulf of Mexico, where it is not eastward, bursting into the Atlantic Ocean between Florida and Cuba.
This current is known as the North Atlantic drift as the Gulf Stream. Once it leaves the American coast, each ocean has its system of ocean currents. The ocean currents of the Atlantic and Pacific oceans show a familiar pattern.
Example of ocean currents with climate change
The distance from the ocean current significantly affects the climates of both inland and coastal regions because of the moderating effects of oceans on coastal temperatures. During the day, insulation from the Sun travels through the atmosphere and heats the continent’s land.
This heat from the Sun can only penetrate the top layer of the ground because the land is solid. It means that the land heats highly quickly. But that, very little of this heat is stored because only the top few centimeters receive any of this heat.
The ocean, on the other hand, is transparent. It means the sun’s rays can penetrate the water to a greater depth and, therefore, the heat stored to a greater depth. Air over the land heats very quickly and especially in summer. Temperatures climb fast and can often go well into the 30s, depending on the place. Therefore in summer, when the temperatures rise quickly over the land, the air over the oceans is cooler.
- The ocean heats more slowly, blowing over the land preventing the coastal temperatures from rising too high. One of the main reasons coastlines worldwide, especially those near the tropics, are not permanently scorching hot during the day. It is because the ocean currents that flow past moderate their temperatures and cool them.
In winter, the opposite process occurs because the land loses its heat very quickly. The air over the land cools quickly as well. The oceans, however, have lots of heat stored. It causes the air over the seas to remain relatively warm. Thus warm air then flows over the land and warms the coastal temperatures. It prevents them from getting too cold.
For example, Durban is along South Africa’s east coast and sits along the warm Indian Ocean. Durbin’s average summer temperature is around 26 degrees Celsius. Its average winter temperature is about 18 degrees Celsius.
On the other hand, Kimberley is 620 kilometers inland from Durban and has no ocean to moderate its temperatures. As a result, its summer averages are much higher than turbines at 31 degrees. Its winters are much lower than turbines or colder than 12 degrees.