The Role of Biology in the Climate System: Long Term Climate Regulation. Earth History, Gaia and Human Perturbations of Biological Systems

Transcription

1 The Role of Biology in the Climate System: Long Term Climate Regulation Earth History, Gaia and Human Perturbations of Biological Systems

2 How would the Earth differ if Life had not evolved or expanded? ~5 differences Geographic perspective (global) Temporal perspective (4.5 b.y.) 4 5 small groups ~ 10 min.

3 Additional Planetary Questions 1. Where did all the water go that must have been ejected into the atmosphere of Venus? 2. Where did all the Carbon Dioxide go that must have been ejected into the atmosphere of Earth? 3. Why does the Earth have so much Oxygen in its atmosphere and Venus has none? Check facts on web page for today's session h.html

4 A Brief History of Earth s Climate Earth formed 4.6 billion years ago Earth, Mercury, Venus and Mars are composed principally of rock (iron and silicate minerals) from the hot, inner parts of the condensing nebula Outer parts of the nebula, icy/volatile (low boiling point) materials such as water, methane and ammonia condensed to form Jupiter, Saturn, Uranus and Neptune Earth developed a thick CO 2 -rich atmosphere and a deep ocean Despite lower solar luminosity at the time (ca. 30% lower sun brightens as it ages), the earth was warm because of the intense greenhouse effect The sun then brightened, and atm CO 2 decreased (due to negative feedback in the weathering cycle) and climate was maintained at levels favorable to life

5 Formation and History of the Earth's Atmosphere and Oceans Impact degassing up to ca. 3.8 billion years ago: bombardment of the surface by smaller planetesimals released water, CO 2 and other volatile compounds into the atm Also contributions from volcanoes and hot springs Also contributions to atm from comets and other volatile-rich asteroids Early atm w/o O 2, but rich in CO 2 (1,000-30,000x present!), N 2, H 2 S, CO 2, HCL, H 2 O High CO 2 because small continents (they accrete over time by plate tectonics) So no place to store carbon via silicate weathering

6

7 Removal of atmospheric CO 2 by weathering + (shorter term deposition of limestone and organic matter on ocean floor) Weathering million years

8 Long Term Feedbacks in the Weathering/Carbonate-Silicate Cycle Temperature Increased temperature increases reaction rates, including chemical weathering Net rainfall Increased water increases weathering as water is required water for dissolution and transport Increase atmospheric CO 2 leading to warmer world, leading to wetter world, leading to more weathering thereby decreasing atmospheric CO 2

9 First evidence of life 3.8 billion years ago: procaryotes, did not produce O 2 Procaryotes=single-celled organisms w/o nuclei First procaryotes that did produce O 2 evolved around 3.5 billion years ago: CO 2 + H 2 O -> CH 2 O + O 2 Oxygen started to accumulate and ozone O 3 formed a protective layer against uv radiation Life Increasing oxygen resulted in formation of Fe (iron) deposits 2.2 to 1.6 billion years ago: the solubility of Fe in water is a function of the oxygen concentration

10 Banded Iron Formations bya US, Australia, South America

11

12 Life, continued Evidence for higher lifeforms abundant after 600 million years, fossil record, only 13% of Earth's history! (Cambrian) Prior 600 million years ago (Precambrian) very little preservation Production of O 2 by photosynthesis was balanced by respiration (reverse of reaction above) First humans:~4 million years ago, homo sapiens 0.4 million years ago An english yard is the distance from the tip of the nose to the end of the middle finger, one stroke of a file on the nail would erase the entire history of humankind

13 Modern Conditions Over the past few hundred million years, Earth s climate has fluctuated between warm and cold conditions, primarily as a result of these inter-related factors: Changes in locations of continents/sea level/mountains induced by plate tectonics Changes in atmospheric CO 2 related to the carbonate-silicate cycle and biology Changes in albedo related to glaciations

14 Devonian period ( Mya): Spread of vascular plants with deep root systems and microorganisms accelerate weathering and decrease atm CO 2 by increasing the CO 2 partial pressure in soils and releasing volatile organic acids that help dissolve rocks (thereby taking up CO 2 )

15 Carboniferous period ( Mya): formation of coal deposits (from burial of peat) buries carbon, decreasing atm CO 2 Biological influences tend to decrease atm CO 2 and cause cooling over the past 500 my

16 Mesozoic Era ( mya = Dinosaurs) Faster sea floor spreading More subduction of deep sea carbonates Faster release of CO 2 through carbonate metamorphism More release of CO 2 by outgassing at spreading ridges Higher sea level (because of hot, high oceans) result in less continental weathering No ice at poles for ice/albedo feedback Physical causes for elevated CO 2 and warmer climates

17 Climate Evolution on Venus and Mars Like Earth, Venus and Mars started with water, carbon, silicate

18 Additional Planetary Questions 1. Where did all the water go that must have been ejected into the atmosphere of Venus? 2. Where did all the Carbon Dioxide go that must have been ejected into the atmosphere of Earth? 3. Why does the Earth have so much Oxygen in its atmosphere and Venus has none? Check facts on web page for today's session h.html

19 Venus At first glance, if Earth had a twin, it would be Venus. The two planets are similar in size, mass, composition, and distance from the Sun. But there the similarities end. Venus has no ocean. Venus is covered by thick, rapidly spinning clouds that trap surface heat, creating a scorched greenhouse-like world with temperatures hot enough to melt lead and pressure so intense that standing on Venus would feel like the pressure felt 900 meters deep in Earth's oceans. These clouds reflect sunlight in addition to trapping heat. Because Venus reflects so much sunlight, it is usually the brightest planet in the sky.

20 Venus Closer to the sun so solar flux at surface of Venus is 1.9x that of Earth So atmosphere becomes so warm and full of water vapor that virtually no infrared radiation from the surface is allowed to escape to back to space Runaway greenhouse: surface becomes warmer and warmer, temperatures as high as 1500 K Oceans evaporate all water turns to vapor (so no silicate weathering) and then is lost by photodissociation and escape of hydrogen into space Turns hot and dry with dense swirling clouds of sulfuric acid

21 Mars

22 Mars Solar flux only 43% that of Earth so solar heating so low that CO2 itself condensed forming clouds and polar ice caps which are mixtures of CO2 and water ice (CO2 ice = dry ice) Was once (before 3.8 bya) warm enough to allow liquid water to flow on its surface Terrain: channels/valleys cut by flowing water Maybe cooled off so quickly because of its small size and therefore small internal radioactive/ geothermal heat source, no plate tectonics Most of CO2 locked into rocks or ice

23

24 Gaia (Ancient Greek Mythology=Goddess of Mother Earth) James Lovelock and Lynn Margulis: Life itself has been responsible for maintaining the stability of Earth s climate Self regulating by feedback loops Organisms can be components of selfregulating, natural systems simply because they influence and are influenced by, the physical environment in which they live

25 Daisyworld? A world populated entirely by white daisies and gray soil (or black daisies) Two component system Temperature Area of white daisy coverage More white daisies, more reflectance (higher albedo), cooler temperatures But daisies have an optimum growth band don t like temperatures too hot or too cold (Monday lecture) If temperatures cool Daisies don t grow as well, leaving enough dark area exposed to absorb sunlight and maintain the temperature within their optimum range What if something causes temperatures to warm above the optimum? The daisies will die off because it is too warm Causing more gray area to be exposed, absorbing more sunlight, and killing more daisies

26 How have/can humans affect(ed) biological systems? How can these changes in biological systems affect climate?

27

28 Purposeful Use of Biology to Modify Climate Carbon trading/reforestation Ocean fertilization with iron Greenroofs Consider How would this approach work? What aspect of the climate system is it designed to affect? Where would it work best? What are the positive and negative side effects? Include social as well as climatological (e.g. asthetics) Is this a good idea? Should it be widely promoted/used?

29