Global Warming and the Venus Greenhouse Effect 11 October 2017

Venus: Global warming gone bad

Earth & Venus: Sister planets? 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?

Terrestrial Planet Atmospheres Table 10.1 Terrestrial Planet Atmospheres © 2014 Pearson Education, Inc.

How do we know Venus’s surface temperature?

How do we know Venus’s surface temperature? low energy long wavelength “redder” cold high energy short wavelength “bluer” hot

How do we know Venus’s surface temperature? the Sun emits light here. T=6000 K Earth emits light here. T=300 K Venus emits light here. T=750

Wavelength of light (in the infrared) How do we know what the clouds are made of? Spectrum of planet with no atmosphere Amount of light observed above the atmosphere Wavelength of light (in the infrared)

How do we know what the clouds are made of? Spectrum of planet with no atmosphere Spectrum of planet with atmosphere Amount of light observed above the atmosphere Amount of light observed above the atmosphere Wavelength at which a molecule in the atmosphere absorbs light Wavelength of light (in the infrared) Wavelength of light (in the infrared)

How do we know what the clouds are made of? (Infrared light)

Two views: Venus atmosphere Figure 10.31 © 2014 Pearson Education, Inc.

Table 10.2 © 2014 Pearson Education, Inc.

Figure 10.18 Climate change causes © 2014 Pearson Education, Inc.

Figure 10.18.1 © 2014 Pearson Education, Inc.

Figure 10.18.3 © 2014 Pearson Education, Inc.

Figure 10.18.4 © 2014 Pearson Education, Inc.

Figure 10.21 © 2014 Pearson Education, Inc.

Figure 10.37 Global warming since 1880 © 2014 Pearson Education, Inc.

CO2 over last 800,000 years Figure 10.38 © 2014 Pearson Education, Inc.

Figure 10.39 © 2014 Pearson Education, Inc.

Pink: Melting ice in Greenland! Figure 10.41 © 2014 Pearson Education, Inc. 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.

A planet with no atmosphere How did Venus get so hot? A planet with no atmosphere Solar radiation comes in Planetary radiation goes out Planetary surface

A planet with an atmosphere How did Venus get so hot? A planet with an atmosphere Solar radiation comes in The greenhouse gases reradiate. Some of the energy goes towards the surface. Planetary radiation goes out, but gets absorbed Greenhouse gases Planetary surface

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”. greenhouse gases heat the surface of the planet rocks and water vaporize and release greenhouse gases Why was Venus hot in the first place?

Earth was also a “runaway greenhouse” at one point! greenhouse gases heat the surface of the planet rocks and water vaporize and release greenhouse gases

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

Figure 10.32 © 2014 Pearson Education, Inc.

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.

© 2014 Pearson Education, Inc.

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. RADAR instrument surface RADAR instruments can map topography.

Venus’s surface was mapped with RADAR. RADAR instrument smooth surface rough surface RADAR instruments can determine roughness.

Venus’s surface was mapped with RADAR. RADAR instrument Reflective surface Absorptive surface RADAR instruments can determine reflectivity.

Venus’s has few small craters. Why? Venus’s has few large craters. Why?

Venus’s has few small craters. Why? Venus has a dense atmosphere. Venus’s has few large craters. Why? Venus’s surface is ‘young’.

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

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.