Climate Regulation. - What stabilizes the climate - Greenhouse effect

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1 Climate Regulation - What stabilizes the climate - Greenhouse effect

2 Last time! Processes that shaped Earth: Volcanism, tectonics! How we retain atmospheric molecules ( escape speed )! A magnetic field can help retain an atmosphere (deflecting the solar wind)

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4 ! The Earth s magnetosphere is cavity carved out in the solar wind by the magnetic field It deflects most solar wind particles, and channeling a few towards the poles creating auroras.

5 Magnetic fields in the Solar System! Only Earth and Mercury amongst terrestrial planets have magnetic fields. Mercury small and has slow rotation (1 rot in 59 Earth days), but have a very large metal core Mars and the Moon have no magnetic fields due to core not liquid enough. " Mars lost most atmosphere when its interior cooled Venus rotates too slow (1 rot in 243 Earth days)

6 Climate Regulation and Change! Long term habitability depends on volcanism, plate tectonics, magnetic fields! The climate on Earth has been stable enough to exist for 4 Gyr. Life needs liquid water oceans must remain at least partially liquid Temperature range for liquid water is not that wide on astronomical scales Earth s climate remarkably stable Why is the long-term climate on Earth stable and warm enough for water to be liquid?

7 ! To just be at the right distance from the Sun is not enough for a body to have liquid water. Moon daytime 125 C (above H 2 O boiling point), nighttime -175 C Sun is slowly brightening (30% brighter today then 4.6Gyrs ago) Earth s average temp based on distance = -16 C Actual temperature is 15 C! Answer is in the Greenhouse Effect

8 The greenhouse effect The trapping of infrared radiation from the surface of the Earth by greenhouse gases in the atmosphere (CO 2, CH 4, H 2 O) Without the greenhouse effect the oceans on the Earth probably would have been frozen

9 ! Sunlight hits Earth, some reflected, some absorbed.! Ground re-radiates infrared photons that will be absorbed by a greenhouse molecule.! Re-emitted in a random direction, slowing down the escape of infrared radiation from the lower atmosphere. Makes is warmer, like a blanket.

10 The greenhouse effect on Venus The greenhouse effect is not intrinsically bad as portrayed in news.! Adding too much greenhouse gases though can cause it to become too hot => global warming! The greenhouse effect on VENUS is responsible for the searing 470 o C temperature! CO 2 is less than 1% of Earth atmosphere, more than 96% of Venus atmosphere!

11 Venus and Earth are nearly the same size volcanic outgassing probably released the same amount of CO 2 What happened with the CO 2 on Earth? At Earth CO 2 dissolved into oceans: Became locked in sedimentary carbonate rocks (limestone) Containing ~170,000 times as much CO 2 as our atmosphere The Carbon Dioxide Cycle regulates the surface temperature by varying the amount of CO 2 in the atmosphere

12 Atmospheric CO 2 dissolves in rainwater Acid rain erodes rocks, rivers carry the minerals to the oceans In the oceans, calcium combines with dissolved CO 2 and falls to the ocean floor making carbonate minerals accumulate as limestone Plate tectonics carry carbonate rocks to subduction zones into the mantle Some melt and release CO 2 through volcanoes

13 The CO 2 cycle acting as a thermostat

14 ! If the temperature of the Earth warms up CO 2 cycle speeds up the formation of carbonate minerals in the oceans, thus pulling more carbon dioxide out of the atmosphere.! If the temperature of the Earth cools CO 2 cycle slows down the formation of carbonate minerals in the oceans, thus pulling less carbon dioxide out of the atmosphere. Perfect! Global warming will fix itself!! Unfortunately not.! The CO 2 cycle cannot easily correct the CO 2 due to industrialization because it operates far too slowly to correct for any short-term changes! The feedback mechanism takes about 400,000 years

15 Earth s climate change over time! Ice ages = Cooling period (global average temperature drops by a few degrees)! During the past few million years, ice ages were probably caused by small changes in the Earth s axis tilt.

16 On long time scale - the sun brightening and the migration of continents influenced the climate On shorter time scale small, cyclical changes in Earth s rotation and orbit making season more or less extreme Greater tilt = more extreme seasons, warmer summers and cooler winters, prevents ice from building up warmer planet

17 Snowball Earth! Long and deep ice ages between million years ago, billion years ago Glaciers advanced to the equator, oceans freezing worldwide 90% sunlight reflected by ice compared to 5% by water Surface cooled more! The CO 2 cycle halts After long time, sufficient amount of CO 2 outgassed by volcanoes Greenhouse effect warms up the Earth again! Geological evidence for fast temperature increase in the end of a snowball episode Could impact life coincides with the Cambrian explosion for example

18 Summary Earth s habitability! Major factors that kept earth habitable for the past 4 billion years Volcanic outgassing (greenhouse gases and water) Protective effect of its magnetic field The greenhouse effect warmed the planet for the water to be liquid The moderate greenhouse effect is maintained by the self-regulating CO 2 cycle Earth axis tilt and rotation influences its climate The climate regulation is not perfect, leading sometimes to snowball earth

19 Formation of the Moon case study of the process of science Example of the process of science, ch. 4.6 Models: 1. Moon formed along with Earth during accretion calculations did not support this model; the Moon average density is much lower than Earth s 2. Moon has been an independent planet captured into Earth s orbit improbable to loose its orbital energy; only likely with small bodies friction with gas surrounding the planet Mars 3. Young molten Earth spinning so fast it split into 2 pieces improbable to spin so fast 4. Impact with a body the size of Mars

20 ! The currently accepted theory for the formation of the Moon is the giant impact model: Moon created from material blasted from the Earth after an impact with a body the size of the planet Mars! Supporting evidence: Overall composition of Moon rocks returned from the Apollo program similar to the composition of Earth s mantle material, except for the lack of volatile elements