1. Carbon Dioxide AN ASTRONOMICAL PERSPECTIVE Presented by Stephen Schneider Deborah Carlisle June, 2011

2. Atmospheres of the Terrestrial Planets All the planets had similar sources of gas available: comets impacting them and volcanic outgassing. Earths atmosphere is about 1% of Venuss; Marss is about 1% of Earths. Why such a difference? Venus and Mars both have ~95% CO 2 atmospheres, but Earth has <<1% CO 2.

3. Atmospheres and Sunlight Sunlight is the source of heat for the terrestrial planets, and it grows weaker with distance. Note that the Moon is cooler than the Earth, even though they are at the same distance from the Sun. Atmospheres can block sunlight, but they can also prevent absorbed heat from leavingthicker atmospheres generally lead to more warming. PlanetMercuryVenusEarth & MoonMars Simple Temp prediction 420 K310 K260 K210 K Actual Temp420 K740 K290 K & 260 K220 K

4. Global Warming and IR Light Carbon dioxide (and water vapor) absorb infrared radiation, mostly reradiated from the surface, trapping it and warming the surface.

5. Is Current Global Warming Caused by Humans? Some scientists have questioned whether global warming was caused by humans because the Sun varies and roughly matches the recorded changes. Over the last decade, though the curves diverge, indicating the Sun is not the cause.

6. Life and Earths Atmosphere 0.1 mm By about 3 Gyr ago, there were photosynthetic cyanobacteria. The cyanobacteria convert CO 2 to other molecules releasing oxygen. By about 2 Gyr ago, eukaryotic life (cells that contain nuclei) formed.

7. The Earliest Life By about 3 Gyr ago, there were photosynthetic cyanobacteria. The cyanobacteria convert CO 2 to other molecules releasing oxygen. By about 2 Gyr ago, eukaryotic life (cells that contain nuclei) formed. 0.1 mm Photosynthesis polluted the Earth with oxygen!

8. 8 Complex Life Forms Land life requires oxygen to be shielded from solar UV. Trilobytes were some of the first complex creatures to appear about 550 Myr ago. By 250 Myr ago dinosaurs and early mammals evolved. Hominids developed 5.5 million years ago Homo Sapiens evolved only 500,000 years ago Weve all been altering our atmosphere!

9. CO 2 has declined as Sun becomes more luminous. Temperature has a complex behavior and seems to switch between warm and cold phases. Our Changing Global Balance

10. Recycling Carbon We are putting more carbon into the atmosphere. Natural processes do not appear to be taking it back out.

11. Measuring Atmospheric Carbon A liter of pure gaseous CO 2 contains about 0.5 grams of carbon (at standard atmospheric pressure and temperature). How can we measure the amount of carbon that different sources add to the atmosphere?