Lecture 4: January 20, 2012
Possible Causes of Climate Change
Why do we care about short-term when climate is long-term?
• In terms of planning and how it affects humans
• Perturbation – could push Earth’s system into different state
• Want to predict climate, need to understand current climate
• Correlation: two patterns are related
• Causation: related by chance; they actually aren’t related
Testing Causes of Climate Chance
• Has some external force changed in a similar way as observed climate?
• Is there a scientific explanation? Does the external force change the balance?
• If there are multiple hypothesizes, can we separate them?
Greenhouse Gas Strengths
• How long they last in the atmosphere
• Multiple CO2 lifetimes years because of the CO2 cycle
• CO2 molecule has same effect on global warming potential at any age
• CO2 is the dominant GHG: compotision + effect
• Humans are not directly responsible for water vapour GHG
• N2O from fertilizer and industrial processes
• CO2, CH4, N2O : hockey stick graph over last 10 000 years; has skyrocketed over last 200 years
• CO2 levels from ice core samples miles deep in Antartica
• 2012: 390 ppm
• 2005: 378 ppm
• prior to 2005: never above 300 ppm
Where does the Carbon come from?
• Isotopes: different number of neutrons
• 99% Carbon-12
• 1% Carbon-13
• Carbon-14 is radioactive, naturally produced in the upper atmosphere
• There is a constant level of Carbon-14 in the atmosphere, it starts decaying when something dies
• As CO2 in atmosphere increases, Carbon-14 decreases
• Carbon-12 is organic because it is easier for plants to take in Carbon-12 than 13 because it’s atomic weight is less
• CO2 is made of Carbon-12
• Increase in CO2 in atmosphere is due to fossil fuels because it is organic, Carbon-12