Like anything else that’s white, clouds reflect a lot of sunlight. That’s why objects also appear white. But do clouds absorb solar radiation? And, if yes, how does that reflect on climate, solar systems, and all life on Earth?
The clouds are absorbing a lot of the heat coming from the sun. But not all clouds are good at absorbing solar radiation.
Let’s learn all about clouds.
The water droplets and ice crystals in clouds are very good at absorbing infrared radiation, which is heat.
That’s why when you fly in an airplane through a cloud, it can sometimes feel cold even though the sun is shining.
Without clouds, the Earth would be too hot for us, so we’re very glad they’re there!
Therefore, clouds help to cool the Earth by reflecting some of the sunlight back out into space before it reaches the ground and heats things up. This happens because clouds are very good at reflecting short-wavelength radiation, like visible light. But they’re not so good at reflecting long-wavelength radiation, like infrared radiation. Infrared radiation is heat, and it’s the radiation that we feel as warmth when it hits us.
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How Do Clouds Form?
We need to know a bit about how clouds form.
Clouds comprise tiny water droplets or ice crystals.
These droplets are so small that they can stay suspended in the air.
The way these droplets stay suspended is by constantly absorbing and releasing water vapor.
So when the sun’s radiation hits the surface of the earth, the ground heats and warms the air above it.
This warm air then rises, carrying water vapor with it.
As the air rises, it eventually reaches a point where the temperature is cool enough for the water vapor to condense and form clouds.
Do Clouds Absorb Solar Radiation?
It depends on the type of cloud.
For instance, if you have ever been outside on a hot day and felt cooler under a tree, that’s because the leaves of the tree were blocking some of the sun’s radiation from reaching you.
In a similar way, thick clouds can block some of the sun’s radiation from reaching the earth’s surface.
However, thin clouds actually have the opposite effect and can actually trap heat near the earth’s surface, making it warmer.
So it really all depends on the type of cloud.
Do Clouds Affect the Climate on Earth?
Have you ever noticed how important clouds are in determining a day’s minimum and maximum temperatures?
Clouds cover about 60% of the earth’s surface.
They affect both the visible and infrared radiation balance of Earth.
Clouds, in particular, are a great way to learn about climate change.
Typically, low-lying thick clouds reflect sunlight and cool the Earth’s surface.
High-thin clouds mostly allow sunlight through but also trap some heat that escapes from the planet as infrared radiation.
Because of this, less heat goes into space, which keeps the Earth’s surface warmer.
The altitude, size, and composition of a cloud all influence whether it will heat or cool the surface.
Although clouds have a cooling impact on the average, the balance between warming and cooling actions is tight.
Clouds are also crucial to the hydrological cycle as a vital link in water circulation, which involves transporting water and heat from the seas to land surfaces. We know that:
- By reflecting sunlight, clouds have a cooling effect on the Earth. The tiny drops or ice particles in clouds scatter between 20 and 90% of incoming sunlight, giving them their bright, white appearance. From space, we can see that clouds look bright against dark bodies of water. If there were no clouds at all, the Earth would absorb nearly 20% more heat from the sun than it does now. Earth would have to be warmer by approximately 12°C in order to be in radiation balance.
- Clouds reflect sunlight back into space, just as they would on a hot summer’s day at the beach.
- Clouds warm the planet by absorbing infrared radiation emitted from the surface and reradiating it down. The process resembles that of putting on a blanket, trapping heat like one, and slowing the rate at which the surface can cool. Clouds have a blanket effect, which warms the surface by about 7°C. As a result, at least under current cloud distribution worldwide, clouds have a net cooling effect of 5°C on the surface.
What Kind of Light Does the Sun Emit?
The nature of the world’s climate system is to maintain a balance between the energy supplied by the sun and that radiated away from Earth. We call this “the Earth’s energy budget.”
The radiation budget of the planet includes its surface, atmosphere, and clouds. Solar radiation refers to solar energy.
The lion’s share of radiation exists as “visible” wavelengths, which our eyes can detect.
This type of visible radiation is what we refer to as “shortwave.”
The average temperature of a system’s radiating surfaces determines both the amount and frequencies of energy that are emitted.
The sun’s photosphere has a temperature of more than 5500°C (9900°F).
Most of the sun’s energy does not reach Earth because it scatters in every direction, and only a minor amount reaches the Earth.
What is Cloud Albedo?
Reflection and emission are two methods by which energy leaves the planet.
A portion of the solar energy that reaches Earth is reflected out to space in the same short wavelengths in which it arrived.
The albedo refers to the amount of solar radiation that is reflected into space and varies significantly across the globe.
Different areas on the earth have varying albedos.
For instance, ocean surfaces and rainforests have low albedos and only reflect a tiny fraction of the sun’s energy.
Deserts, ice, and clouds have high albedos though, reflecting about 30 percent of the sun’s energy into space.
Because a cloud typically has a higher albedo than the surface beneath it, when there is no cloud, the cloud reflects more shortwave radiation back to space than the surface does and thus removes less solar energy from the system.
Because of this “cloud albedo forcing,” alone, it causes an overall cooling or “negative forcing” of Earth’s climate.
The Earth also emits energy as electromagnetic radiation.
The solar radiation that the Earth absorbs causes it to heat until it emits as much energy back into space as it originally received from the sun.
However, because the Earth only absorbs a tiny fraction of the sun’s total energy, it stays cooler than the sun and thus emits significantly less radiation.
Most of the emitted radiation from the Earth is at longer wavelengths than solar radiation.
Unlike solar radiation, which is visible to human eyes, long-wave radiation from the Earth is mostly invisible to us.
When a cloud absorbs long-wave radiation being sent out by the Earth’s surface, the cloud re-emits some of that energy back into outer space and some of it back down toward the surface.
A cloud’s emission varies depending on the temperature of said cloud and other conditions, such as thickness and type of particles.
The top part of a cloud is colder than Earth’s surface if formed in a place with no previous clouds.
This global cooling effect happens because the cold air near the energy of the top trap beneath the cloud, preventing it from being released into space.
The trapped energy will raise the temperature of the surface and atmosphere until the long-wave radiation to space balances the incoming absorbed short-wave radiation.
This process, known as cloud greenhouse forcing, results in climate warming or “positive forcing” when taken alone.
What Is “Greenhouse” Forcing?
The higher a cloud is in the sky, the colder its top surface and the greater its cloud greenhouse forcing is.
If the Earth were to lose its atmosphere, the surface temperature would drop so low that emitted radiation would eventually equal absorbed solar energy.
However, because there is an atmosphere, it creates a greenhouse effect which keeps the planet warm and habitable.
With less air pollution, incoming shortwave solar radiation can reach the Earth’s surface more easily.
The surface emits long-wave radiation, most of which escapes into space; however, some is absorbed by greenhouse gases.
These gases then radiate energy in all directions—including back to the Earth’s surface.
As a result, the surface becomes heated and emits even more radiation.
Gases such as water vapor, carbon dioxide, and methane that trap heat from the sun cause the greenhouse effect. The planet’s surface is sufficiently warm to support life because of this trapped energy.
Aside from the heating impact of clear air, clouds in the atmosphere aid to moderate Earth’s temperature.
The balance of cloud albedo and cloud greenhouse forcing determines whether a specific cloud type will enhance or counteract the air’s natural warming of the surface of the Earth.
While high-thin cirrus clouds can enhance the heating effect, low-thick stratocumulus clouds have the opposite effect.
Deep convective clouds are usually neutral in terms of their impact on the atmosphere.
Overall, all different clouds work to cool down the Earth’s surface temperature.
Clouds help to cool the Earth by reflecting some of the sunlight back out into space before it reaches the ground and heat things up.
This happens because clouds are very good at reflecting short-wavelength radiation, like visible light.
But they’re not so good at reflecting long-wavelength radiation, like infrared radiation.
Infrared radiation is heat, and it’s the radiation that we feel as warmth when it hits us.
So when clouds reflect visible light back into space, they’re helping to keep us cool by reflecting some of the sun’s heat away from us. Thanks, clouds!