Greenhouse effect

L10

Points about the climate system.

• the climate system is forced or influenced by various external forcing mechanisms, the most important of which are the Sun and the Earth’s rotation

• the effect of human activities on the climate system is considered as an external force and thus it influence changes in it

• the climate system determines the weather at a particular place of the Earth

How and why does solar irradiance at the Earth’s surface differ than that of a blackbody radiator at 5800K?

• the difference can be seen on the energy spectra

• the biggest difference is seen when looking at the energy maximum.

• the blackbody curve is a mathematical estimation and therefore it is smooth

• if the Sun was a perfect blackbody, it would emit a spectrum as described by the Planck’s equation

• But both the sun and the earth have an atmosphere around them composed of atoms and molecules that can absorb some of the sunlight

• creating gaps in the blackbody curve.

What is the solar constant 1370 W/m²?

• the solar constant is the amount of solar energy received per square meter at the top of the atmosphere on a flat surface held perpendicular to the sun’s rays

• e-so every sq m of Earth’s surface receives less than 1370 W

Can the 1st law of thermodynamics be applied to the energy budget of the Earth’s atmosphere?

• states that energy can be transferred from one system to another un many forms, but it cannot be created or destroyed

• thus, any energy that is lost during one process will equal the same amount of energy gained during another process

• the balance between incoming energy from the Sun and outgoing energy form the Earth that drives our climate is the direct consequence of the 1st law of thermodynamics

Why is planetary albedo important in the energy budget of the Earth? What would happen if the albedo would change form 0.3 to 0.5?

• planetary albedo determines the fraction of sunlight reflected away from the surface and so affects the amount of absorbed shortwave radiation.

• if it would increase, more of the shortwave radiation would be reflected and surface would cool down

• clouds & aerosols increase the atmosphere’s albedo

We say that the longwave radiation is trapped in the Earth’s atmosphere because:

• it is emitted and absorbed multiple times and each time a bit of it remains

How is solar radiation scattered in the atmosphere and what effect does this scattering have on the energy budget of the Earth?

• scattering happens on gasses, aerosols, cloud droplets and ice particles

• part of it is reflected back to space and the other part is converted from shortwave to longwave radiation

What direct and indirect effect do aerosols have on radiation budget of the Earth?

• Direct effect:

  • is the absorption and scattering of radiation which means less direct radiation reaches the surface

• indirect effect:

  • is the effect on radiation via modification of cloud properties

    • aerosols act as CCN

    • because there are more nuclei, the cloud forms more and smaller droplets

  • this create brighter, more reflective clouds that bounce significantly more sunlight back out to space

Explain the connection between CO2 and temperature.

• as the ocean temperature rises

• ocean releases CO2 into the atmosphere

• in turn, this release amplifies the warming trend, leading to more CO2 being released into the atmosphere.

• increasing CO2 levels become both cause and effect of further warming