Carbon DioxideCarbon DioxideAN ASTRONOMICAL PERSPECTIVEAN ASTRONOMICAL PERSPECTIVE

Presented by Presented by

Stephen Stephen SchneiderSchneider

Deborah CarlisleDeborah Carlisle

June, 2011June, 2011

Atmospheres of the Terrestrial Planets

• All the planets had similar sources of gas available: comets impacting them and volcanic outgassing.

• Earth’s atmosphere is about 1% of Venus’s; Mars’s is about 1% of Earth’s. Why such a difference?

• Venus and Mars both have ~95% CO2 atmospheres, but Earth has <<1% CO2.

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 leaving—thicker atmospheres generally lead to more warming.

Planet Mercury Venus Earth & Moon Mars

Simple Temp prediction

420 K 310 K 260 K 210 K

Actual Temp 420 K 740 K 290 K & 260 K 220 K

Global Warming and IR Light

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

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.

Life and Earth’s Atmosphere

0.1 mm

• By about 3 Gyr ago, there were photosynthetic “cyanobacteria.”

• The cyanobacteria convert CO2 to other molecules releasing oxygen.

• By about 2 Gyr ago, eukaryotic life (cells that contain nuclei) formed.

The Earliest Life

• By about 3 Gyr ago, there were photosynthetic “cyanobacteria.”

• The cyanobacteria convert CO2 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!

8Complex 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• We’ve all been altering our atmosphere!

• CO2 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

Recycling Carbon

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

Measuring Atmospheric Carbon

• A liter of pure gaseous CO2 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?