Global Warming and the Venus Greenhouse Effect

24 February 2015

Venus: Global warming gone bad

Earth & Venus: Sister planets?

Venus Earth

Mass 5x1024 kg 6x1024 kg

a (semi-major axis)

0.7 AU 1 AU

T at surface ~750 K ~300 K

P at surface ~90 atm ~1 atm

atm composition

N2 and H2O clouds

CO2 and H2SO4 clouds

What is the boiling Temp of water?

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Table 10.1

Terrestrial Planet Atmospheres

How do we know Venus’s surface temperature?

How do we know Venus’s surface temperature?

high energy

short wavelength

“bluer”

hot

low energy

long wavelength

“redder”

cold

How do we know Venus’s surface temperature?

Earth emits light here. T=300 K

the Sun emits light here. T=6000 K

Venus emits light here. T=750

How do we know what the clouds are made of?

Wavelength of light (in the infrared)

Am

ount

of l

ight

obs

erve

d ab

ove

the

atm

osph

ere

Spectrum of planet with no atmosphere

How do we know what the clouds are made of?

Wavelength of light (in the infrared)

Wavelength of light (in the infrared)

Am

ount

of l

ight

obs

erve

d ab

ove

the

atm

osph

ere

Am

ount

of l

ight

obs

erve

d ab

ove

the

atm

osph

ere

Wavelength at which a molecule in the atmosphere absorbs light

Spectrum of planet with no atmosphere

Spectrum of planet with atmosphere

How do we know what the clouds are made of?

(Infrared light)

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Figure 10.31

Two views:Venusatmosphere

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Table 10.2

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Figure 10.18

Climate change causes

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Figure 10.18.1

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Figure 10.18.3

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Figure 10.18.4

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Figure 10.21

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Figure 10.37

Global warming since 1880

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Figure 10.38

CO2 over last 800,000 years

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Figure 10.39

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Figure 10.41

Pink: Melting ice in Greenland!

How did Venus get so hot?

Remember - all gases absorb light at specific wavelengths.

“Greenhouse” gases (like carbon dioxide, water and methane) like to absorb in the infrared wavelengths.

Planets emit light at infrared wavelengths (same as human bodies).

Conclusion? “Greenhouse” gases don’t lett the heat from the planet escape.

How did Venus get so hot?

Planetary surface

A planet with no atmosphere

Solar radiation comes in

Planetary radiation goes out

How did Venus get so hot?

Planetary surface

A planet with an atmosphere

Solar radiation comes in

Planetary radiation goes out, but gets absorbed

The greenhouse gases reradiate. Some of the energy goes towards the surface.

Greenhouse gases

How do greenhouse gases get into the atmosphere?

Water: evaporation

CO2: vaporization of rocks, release from traps, vaporization of biotic material (like fossil fuels), respiration

Methane: release from traps, biology (bacteria, cows, rice)

Venus is an example of a “runaway greenhouse”.

rocks and water vaporize and release greenhouse gases

greenhouse gases heat the surface of the planet

Why was Venus hot in the first place?

Earth was also a “runaway greenhouse” at one point!

rocks and water vaporize and release greenhouse gases

greenhouse gases heat the surface of the planet

Why did the Earth cool, but Venus stay so hot?

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Figure 10.32

Why did the Earth cool, but Venus stay so hot?

Ideas: Oceans?

Biology?

It probably has to do with water, but why the Earth has water and Venus doesn’t is not well

understood. It MAY be that water allowed plate tectonics to occur, and when the oceanic plates

subduct, they take CO2 with them.

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The Surface of Venus

Venus’s surface can’t be viewed in visible light. The atmosphere absorbs most visible light.

Radio light reaches the surface.

Venus’s surface was mapped with RADAR.

surface

RADAR instrument

RADAR instruments can map topography.

Venus’s surface was mapped with RADAR.

smooth surface

RADAR instrument

RADAR instruments can determine roughness.

rough surface

Venus’s surface was mapped with RADAR.

Reflective surface

RADAR instrument

RADAR instruments can determine reflectivity.

Absorptive surface

Venus’s has few small craters. Why?

Venus’s has few large craters. Why?

Venus’s has few small craters. Why?

Venus’s has few large craters. Why?

Venus has a dense atmosphere.

Venus’s surface is ‘young’.

How are craters on Venus different from craters on other bodies?

Venusthe moon

Venus’s surface is covered with volcanic features.

How can you tell impact craters from volcanic calderas?

What does the brightness mean in these images?

Venus’s surface is covered with volcanic features.

Few craters have been altered by lava.

What does this mean?

If lava lies over an existing crater, then the crater came first.

Venus: Take-away messages

•Venus’s bulk properties (mass, size, distance from sun) are similar to Earth.

•However, Venus’s atmosphere has a lot of CO2 and therefore its surface is very hot.

•Exactly why Venus and Earth evolved in different ways is not well understood, but is probably related to water.

•Volcanism is an important process on its surface, but may not have been active recently.

•Venus’s entire surface is ‘young’, so some global resurfacing event occurred.