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By -:IshaSubhranshuRiteshDeepakshriraj

What is the

Greenhouse

Effect?

The ‘Greenhouse Effect

Radiative equilibrium works for Mercury (no atmosphere) and just about for Mars (thin atmosphere)The disagreement for Venus and the Earth is because these two planets have atmospheres containing certain gases which modify their surface temperatures.This is the ‘Greenhouse Effect’ in action:

Earth’s surface is 34°C warmer than if there were no atmosphereVenus has a ‘runaway’ Greenhouse effect, and is over 400°C warmerMars atmosphere slightly warms its surface, by about 10°C

•The existence of the Greenhouse Effect is universally accepted (it is not controversial), and it links the composition of a planet’s atmosphere to its surface temperature.

The result is a mild greenhouse

effect…not too hot, and not too cold,

just the right temperature for most of

the water to stay in liquid phase, and

some to stay in gas phase in the

atmosphere on the surface of the Earth.

The Earth’s atmosphere is all around us. It is the air we breathe.

Greenhouse gases in the atmosphere behave much like the glass panes in a greenhouse.

Sunshine enters the Earth’s atmosphere passing through the blanket of greenhouse gases.

As it reaches the Earth’s surface, land, water, and biosphere absorb the sunlight’s energy! Once absorbed this energy is sent back into the atmosphere.

Without these gases, heat would escape back into space and Earth’s average temperature would be about 60 º F colder.

Because of how they

warm our world, these

gases are referred to

as greenhouse gases.

Some of the energy passes back into space.

Much of it remains trapped in the atmosphere by the greenhouse gases, causing our world to heat up.

Greenhouses work by trapping heat from the sun.

The glass panels of the greenhouse let in light but keep heat from escaping.

Most greenhouses look like small glasshouses.

Green houses are used to grow plants, especially in the winter.

This causes the greenhouse to heat up much like the inside of a car parked in sunlight, and keeps the plants warm enough to live in the winter.

Without the greenhouse effect, the Earth would not be warm enough for humans to live.

But if the greenhouse effect becomes stronger, it could make the Earth warmer than usual.

Even a little warming

causes problems for

plants and animals.

The primary components of Earth’s atmosphere, N2 and O2 do not have absorption in the IR wavelength range, therefore, do not have a significant role in setting the surface temperature of the planet…Greenhouse gas are efficient in absorbing IR light…

The most important greenhouse gases are:H2O – Water vapor.CO2 – Carbon DioxideCH4 – methaneThe most abundant greenhouse gas in Earth’s atmosphere is water vapor. Most of the greenhouse heating of Earth’s atmosphere is due to Water vapor absorption of IR radiation emitted by Earth, and then transferring the energy to the surrounding air molecule

The condition is just right!

• The combination of three factors: Distance to the Sun, the

albedo, and the greenhouse effect, make it possible for water

to stay on Earth.

• N2 and O2 are not greenhouse gas.

• Not much CO2 in the atmosphere.

• Variable amount of H2O in the atmosphere…regulated by the

temperature.

Water On Earth

The terrestrial planets were built from rock and planetesimals. No gases or water can

condense at the high temperature near the Sun. So, where did the water on Earth

come from?

• The water on Earth (and other terrestrial worlds) most likely was brought over

by the comets during the period of heavy bombardment about 4 billion years

ago…

• These water (and other gases) were trapped in the interior, and released by

volcanic activities…by Outgassing

Was it always like this on Earth?

• Yes. Water was plentiful throughout most of Earth’s history, for

about three billion years.

• No! Geological evidences suggest that Earth used to be covered

by ice about 600-700 million years ago

Snowball Phase.

How did Earth recover from the snowball phase?

• Once the water was frozen, CO2 can no longer be removed from

the atmosphere by dissolving in water interruption of the

CO2 cycle.

• Increased CO2 level in the atmosphere leads to stronger

greenhouse effect, which warms the atmosphere.

• Higher temperature melt the ice restoration of the CO2 cycle.

Earth

Green house effect

Radiation

Reflected radiation by the earth

Christmas fires in Sydney 2001/2002

Smoke aerosolmore reflective than ocean

Land has higher albedothan ocean

Clouds have high albedo

Ice and snow have high albedo

Satellite Measurements of the Earth’s Radiation Budget

– NASA’s Earth Radiation Budget Satellite (ERBS) 1985-1989

Earth formed ~4.6 billion years ago

Originally very hot

Sun’s energy output only 70% of present

Liquid water present ~4.3 billion years

Nitrogen (N2)

Oxygen (O2)

Water (H2O)

Carbon Dioxide (CO2)

Methane (CH4)

Non-Greenhouse

Gases99%

GreenhouseGases

1%

The greenhouse gases are:

Water Vapour

Carbon dioxide

Nitrous Oxide

Methane

CFCs

Our atmosphere contains many natural gases other than ozone. One of these natural gases is carbon dioxide.

Our atmosphere needs a certain amount of this gas. It is carbon dioxide that helpsto keep the Earth warm.

This gas holds in just enough heat from the sun to keep animals and plants alive.

If it held in more heat than it does the climate on Earth would grow too hot for some kinds of life.

If it held in less heat, Earth’s climate would be too cold.

Carbon dioxide gases come from

• Carbon dioxide

Human respiration.

Industrialization

Burning of fossil fuel to generate electricity

Burning of forest (lesser trees)

CO2 is now 1/3 more than before Industrial Revolution

Nitrous oxide makes up an extremely small amount of the atmosphere – It is less than one-thousandth as abundant as carbon dioxide.

However it is 200 to 300 times more effective in trapping heat than carbon dioxide.

Carbon Dioxide is probably the most important of the greenhouse gases and is currently responsible for 60 % of the ‘enhanced greenhouse effect’

Enhanced Human activities, not natural.

The Earth has an atmosphere. So it has Rayleigh scattering and its sky appears blue

The Moon has no atmosphere. So it has no Rayleigh scattering and its sky appears dark

• involves gases smaller than insolation wavelength• scatters light in all directions • most effective at short wavelengths (violet, blue)…

hence, blue sky

How many of you use handkerchiefs instead of tissues and use cloth towels instead of paper towels?

Paper comes from trees. The more of it we use, the more trees that are cut down.

How many of you eat take-out or cafeteria food that is served in foam or plastic containers?

Polystyrene and other plastic containers are made from precious petrochemicals, do not decompose in landfills, and release toxic gases when they are burned in incinerators.

Our home take message…

Each of us must take steps to protect our Earth's climate.

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