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Lec 23: 21 Nov 2011 Chap 9 - 11. Terrestrial Planets.

LAST TIME - Atmospheres of Terrestrial Planets.

TODAY - Changing, Evolving Planets •  Greenhouse Effect •  Runaway Greenhouse Effect •  Water on Terrestrial Planets •  Human Impacts on Earth’s Climate

28 NOV: Jovian Planets (Chaps. 12, 14) 30 NOV: EXAM #3 - Chaps. 9-11, 12,14 5 DEC: Satellites of Jovian Planets (Chap. 13) 14 DEC: Final Exam

Goldilocks and the 3 Planets

see CofC’s impact at www.cofc.edu/ghgas/

Global Properties of the Terrestrial Planets

Mercury Venus Earth Moon Mars

Mass 0.06 0.82 1 0.01 0.11 Diameter 0.38 0.95 1 0.27 0.53 Density (g/cc) 5.4 5.2 5.5 3.3 3.9 uncompressed... 5.2 4.3 4.4 3.3 3.8

Gravity 0.38 0.91 1 0.17 0.38 Albedo (%) 12 59 39 11 15 Atm. Pressure 0 88 1 0 0.01 Temperature (degrees K)

103-623

733 183-333

93- 403

133- 293

The Greenhouse Effect •  ENERGY IN = ENERGY OUT

–  otherwise, Temperature changes –  radiant energy only possible mechanism

•  IN: –  solar radiation (mostly visible)

•  OUT: –  reflected sunlight (visible) –  thermal emission from surface and atmosphere

(infrared, microwave) –  Earth’s interior cooling (infrared; 2700 times less)

•  H2O, CO2, CH4, etc “absorb” infrared –  block a fixed fraction from escaping –  tiny changes in composition can change temperature

Runaway Greenhouse Effect (RAGE) •  start with water and lower temperature on Venus

(Sun’s luminosity was lower) •  raise temperature a little --> H20 evaporates •  water vapor is a greenhouse gas, so temperature

goes up •  this causes more water to evaporate, which

releases dissolved CO2 and more H20 vapor (positive feedback loop)

•  H20 gets to upper atmosphere, where solar ultraviolet breaks it apart

•  Hydrogen --> space; O --> rocks, etc •  D/H ratio confirms that this happened on Venus •  Could it happen to us? (yes, and it will, eventually)

Water on the Surface of Mars •  Runoff Channels (rivers)

–  only in highlands –  large area drainage + main channel + deposition –  between 2 and 4 billion years ago, the climate was very different

(liquid water flowed on its surface)

EARTH MARS

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Water on the Surface of Mars (continued) •  Outflow Channels (floods)

–  near equator, running from south to north –  what was the reservoir? what broke open? –  Pathfinder landed in one of these

•  “Splosh Craters”

Water on the Surface of Mars (continued)

•  Gullies

What Happened to Mars? •  it must have been warmer to have liquid

water flowing on its surface •  it has very little atmosphere now; it must

have had a substantial one in the past •  signs of volcanic activity are not that old, but

no current activity/outgassing •  Possibilities:

–  reverse RAGE (runaway icehouse effect) –  impact – orbit changes – decreasing activity

Astronomical Changes & Climate Drivers •  rapid decrease in solar activity •  clearing phase in early solar system •  gradual increase in solar luminosity •  regular impacts since clearing phase

–  mass extinctions –  cyclic? (rotation of galaxy, nemesis)

•  orbital changes –  month of perihelion; eccentricity –  axis tilt changes

•  gradual spindown (due to tides) •  solar irradiance variations •  ongoing solar activity •  Earth’s changing magnetic field

3 Types of Change:

EVOLUTIONARY

CYCLIC

CATASTROPHIC

molten blob 4.6 GYA

radiate to space: cool

outgas atmosphere

life <--> atmosphere

Astronomical Causes of Climate Cycles

20,000 years

43,000 years

100,000 years

Human-Induced Changes to the Atmosphere 1.  Concentration of Carbon Dioxide IS increasing. Where

does CO2 come from? 2.  Rapid buildup began with the onset of fossil-fuel burning

in the 1800’s.

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Human-Induced Changes to the Atmosphere 3.  Earth’s average temperature IS increasing

(again, there are many natural causes for this). 4.  Increase seems to have accelerated along with

CO2 buildup (lots of “proxy” indicators).

The Facts About Global Warming 1.  Greenhouse Effect is Real

•  well understood, natural phenomenon •  it can be beneficial •  but non-linear, subject to feedbacks,

therefore it is hard to predict changes

2.  Global Warming is Real •  Earth is warming up at a measurable rate •  rate corresponds to...

3.  CO2 Concentration is Increasing •  huge growth corresponds to history of fossil

fuel burning

4.  Earth has always been either heating up or cooling off, and the behavior has been (quasi) cyclic

•  astronomical causes •  geological activity cycles? •  solar activity or luminosity cycles?

5.  Amplitude of natural cycles exceeds current warming trend, but CO2 buildup unprecedented. More importantly...

6.  Timescale of current trend is shorter than any natural cycles (~human lifetime!)

So Why Is There “Controversy”? •  There’s no longer any scientific debate (or

real political debate) over these basic facts.

•  But, how much of the change is man-made, and how much is natural?

•  Does it really matter?

•  So, legitimate debate is over what actions are “prudent”, and which are “knee-jerk”?