Le bilan radiatif terrestre - 1ère enseignement scientifique - Madame SVT

Summary

In this educational video, the concept of Earth's radiative balance is explained in simple terms. The script delves into how the Earth receives solar radiation and how much is reflected back into space, with a focus on albedo, the atmosphere's role in regulating temperature, and the greenhouse effect. It highlights the importance of greenhouse gases in maintaining Earth's temperature but also discusses how human activities are disrupting this balance, leading to global warming. With key mathematical formulas and diagrams, the video aims to help students understand these fundamental scientific processes and their real-world implications.

Takeaways

• 😀 The Earth's radiative balance involves measuring both the incoming solar radiation and the outgoing radiation emitted by the Earth.
• 😀 The Earth receives 342 watts per square meter of solar radiation, which depends on the Earth's size and distance from the sun.
• 😀 The Earth's albedo, or reflectivity, is 0.30, meaning 30% of the incoming solar radiation is reflected back into space.
• 😀 The albedo calculation can be done by dividing the diffused power by the received power, with no units for the final value.
• 😀 The Earth's average surface temperature is 15°C, while the Moon, receiving the same solar radiation, has a surface temperature of -23°C, due to differences in atmosphere and other factors.
• 😀 The atmosphere plays a key role in maintaining the Earth's temperature by absorbing infrared radiation emitted by the surface.
• 😀 Greenhouse gases like water vapor and CO2 absorb infrared radiation, helping to warm the atmosphere and maintain a stable surface temperature above 0°C.
• 😀 Human activities, such as the release of CO2, increase the concentration of greenhouse gases, leading to a rise in global temperatures, also known as global warming.
• 😀 The formula for intensity, which calculates the power per square meter, is I = Power (in watts) / Surface (in square meters).
• 😀 The Earth's radiative balance is dynamic, and any changes in greenhouse gas concentrations can lead to an imbalance, potentially causing global warming.
• 😀 The script concludes by emphasizing the importance of understanding Earth's radiative balance and reviewing the critical schematic for exams.

Q & A

What is the radiative balance of the Earth?

The radiative balance of the Earth refers to the measurement of the radiation received from the sun and the radiation emitted by the Earth. It determines whether the Earth is in thermal equilibrium or not.

What does the term 'albedo' refer to in the context of Earth's radiative balance?

Albedo refers to the proportion of incoming solar radiation that is reflected back into space by the Earth's surface and atmosphere. It is a dimensionless number between 0 and 1, with 0 meaning no reflection and 1 meaning complete reflection.

What is Earth's average albedo, and how does it affect the amount of solar radiation received?

The Earth's average albedo is 0.30, meaning 30% of the solar radiation received is reflected back into space. This reduces the amount of solar energy absorbed by the Earth's surface, impacting its overall temperature.

How does the Earth's atmosphere contribute to maintaining the planet's temperature?

The Earth's atmosphere, containing gases like water vapor and CO2, absorbs infrared radiation emitted by the Earth's surface, trapping heat and warming the planet. This is known as the greenhouse effect.

What role do greenhouse gases play in the Earth’s radiative balance?

Greenhouse gases, such as water vapor and CO2, absorb infrared radiation emitted by the Earth's surface. This helps maintain a stable, warmer temperature on Earth by preventing the heat from escaping into space.

Why does the Earth's surface temperature differ from the Moon's, despite both being close to the Sun?

The Earth's surface temperature is higher than the Moon's because the Earth has an atmosphere that absorbs and retains heat. The Moon, lacking an atmosphere, cannot trap heat, leading to a much colder surface temperature.

What is the significance of human activities in terms of the Earth's radiative balance?

Human activities, especially the burning of fossil fuels, release large amounts of greenhouse gases like CO2 into the atmosphere. This increases the concentration of greenhouse gases, leading to more heat being trapped and causing global warming, disrupting the radiative balance.

How does the formula for intensity (I = power/area) relate to understanding Earth's radiative balance?

The formula for intensity helps quantify the amount of power received per unit area (e.g., watts per square meter). In the context of Earth's radiative balance, it helps calculate the solar radiation received by the Earth and the radiation emitted by its surface.

What is the Earth's average solar radiation, and how is it distributed upon reaching the surface?

The Earth receives an average of 342 watts per square meter of solar radiation. Of this, about 70 watts per square meter are absorbed by clouds, and 240 watts reach the surface. Some of this radiation is reflected by the surface (albedo), while the rest is absorbed.

What happens when the radiative balance is disrupted, such as with the increase in greenhouse gases?

When the radiative balance is disrupted, for example, by increased greenhouse gases, more heat is trapped in the atmosphere, leading to a rise in the Earth's surface temperature. This imbalance is a key factor in global warming and climate change.