Human Caused Global Warming

How do we know it's human caused?

When protons from GCRs (Galactic Cosmic Rays) collide with the nitrogen-14 (seven protons plus seven neutrons in the nucleus) in the air, carbon-14 is created (in addition to other isotopes such as beryllium-10) through a nuclear reaction:

¹⁴N + p → ¹⁴C + n

This means that carbon with a low isotope carbon-14 ratio must come from deep in the ground, out of reach of cosmic rays.

Furthermore, the ratio of O₂ to N₂ has diminished. This is expected from the increased combustion of fossil fuels, in which O₂ combines with C to form CO₂. The oceans have also become more acidic, leading to an increase in CO₂ levels in both the atmosphere and the oceans.

Carbon Output as measured by the EPA:

Summary

Since carbon-14 is created during exposure in the atmosphere, low isotope carbon-14 has not been subject to atmospheric exposure and therefore must have come from underground. In other words, we dug it up, burned it, and now low isotope carbon-14 is in the atmosphere. That is how the two origins of carbon can be clearly identified, by the isotopic signature.

Said another way, low isotope carbon-14 is from fossil fuels, while the rest of the carbon has been in the natural cycle for longer periods. That carbon is stored and released through natural processes such as the normal seasonal carbon breathing that occurs in plant life.

Links

• http://ipcc-wg1.ucar.edu/wg1/FAQ/wg1_faq-7.1.html
  
• http://www.epa.gov/climatechange/emissions/globalghg.html
• http://www.epa.gov/climatechange/emissions/co2_human.html
• http://www.scienceinschool.org/2008/issue8/climate/
• http://en.wikipedia.org/wiki/Isotopic_signature
• How do we know that recent CO₂ increases are due to human activities?