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Climate Change and Climate Change and EarthEarth

Mommy, what were glaciers like?

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GoalsGoals

• The Earth’s unique atmosphere?• How does what we know about natural

climate change relate to what humans can do?

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The Terrestrial PlanetsWorld Atmos.

Compsn.Surface Pressure

Ave Surface Temp.

Winds, Weather

Clouds, Hazes

Mercury He, Na, O 10-14 bar Day: 800FNight: -280F

none none

Venus 96% CO23.5% N2

90 bars 880F Slow winds, acid rain

Sulfuric acid clouds

Earth 77% N221% O2H2O

1 bar 60F Winds, hurricanes, rain, snow

H2O clouds, pollution

Moon He, Na, Ar 10-14 bar Day:260FNight: -280F

none none

Mars 95% CO22.7% N2

0.007bar -60F Winds, dust storm

H2O and CO2 clouds, dust

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Why is Earth so Different?

1. Why do we have oceans of water?• Why do we have so little carbon

dioxide?

• Why do we have so much O2 and N2?

• Why do we have a UV-absorbing stratosphere?

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Concept Test

• The Earth retained so much outgassed water relative to Venus and Mars because:a. The Earth is closer to the Sun than Mars and so was

kept warmer, whereas Venus was too hot.b. The Earth is farther from the Sun than Venus and so

didn’t lose water due to thermal escape, but Mars was too cold and it all froze.

c. Both Venus and Mars lost their water due to evaporation and then UV-dissociation (while much of Mars’ water also froze).

d. The Earth simply outgassed much more water than the other two.

e. None of the above.

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I like Rain

1. Temperature just right.2. Water vapor could rain.3. Liquid oceans didn’t completely

evaporate.4. CO2 could dissolve in oceans.

– 60x CO2 dissolved in oceans as atmosphere.

– 170,000x CO2 in carbonate rocks as atmosphere.

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N and O• Nitrogen is the third most common

product of outgassing.• Water in oceans.• Carbon dioxide in oceans/rocks.• Oxygen is from life.

– Galileo spacecraft performed experimentto see if there was life on Earth.

• Life produces oxygen: O and O2.• Oxygen produces ozone O3.• Ozone absorbs UV-rays, not present on mars or

Venus.

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Goldilocks Planet

• Delicate balance: Earth is just right.– No oceans without

greenhouse gasses.– Without oceans too

many greenhouse gasses.

– Without oceans no life.

– Without life, no ozone.

– No ozone, no life.

• How does Earth maintain this balance?

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Carbon Cycle

Tectonics are crucial!

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Nature’s Thermostat

• Carbon Cycle has negative feedback.• Increasing temperatures lead to

feedback that decreases temperatures, etc.

• Positive and negative feedbacks have nothing to do with desirability of outcome.

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Too Cool

Less Rain

Less CO2 dissolves from oceans.

More CO2 builds up in atmosphere

Increased greenhouse

Heats Up.

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Too Warm

More Rain

More CO2 dissolves from oceans.

Less CO2 builds up in atmosphere

Decreased greenhouse

Cool Down.

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Ice Ages and Cycles

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Concept Test

• Under what circumstances is thermal escape likely to be important?a. Light gases on big planets far from the Sunb. Heavy gases on big planets far from the Sunc. Light gases on small planets near the Sund. Light gases on small planets far from the Sune. Equally well on any kind of gas from any kind

of planet

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Cycles

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Human Input

• Affecting CO2 cycle.

• Moving C from ground to air at increased rate.

• No increase in rate of C from air to ground.

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Mars Today

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Positive Feedback• Fossil Fuels – Increase CO2 to

atmosphere.• Deforestation – decrease CO2 from

atmosphere• Increase CO2 – Increase greenhouse effect• Increase temp – Melting glaciers, ice

sheets, polar caps• Less ice – lower planetary albedo• Lower albedo – Earth absorbs more light• More absorption – Increasing surface

temperatures.

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Homework #18Homework #18

• Due Friday 14-Nov:• Read Hansen and other web articles.• Do: Email me a single question about global

warming of the form “But, I heard that ….”