Lecture 11: Greenhouse Gases

Question 1

How do GHGs absorb/radiate heat

Answer 1

Molecules with more than two atoms (GHGs) can stretch and bend and sometimes the movement of bending vibrations falls within the infrared range (emitted by earth), which causes them to bend more vigorously and send the energy back down to the planet.

Question 2

autotrophs vs heterotrophs?

Answer 2

Autotrophs = acquire energy from sunlight (primary producers)
heterotrophs = acquire energy from sugars (eating the primary producers)

Question 3

What is a chemoautotroph?

Answer 3

Life that uses inorganic substances (besides C) in cellular respiration.
Ex: nitrification or sulphuroxidation

Question 4

What are the ways to measure the relative impact of GHGs?

Answer 4

• Residence time: how long a GHG remains in atmospheric reservoirs
• Global Warming Potential: measured contribution of global warming compared to CO2

Question 5

How is residence time and GWP used together to measure the influence of GHGs on global warming?

Answer 5

Some GHGs can have a smaller global warming potential but also a very small residence time, which can mean that when compared over the same period of time, they can have a larger impact.

Question 6

How is methane produced?

Answer 6

• bacterial species & animals fermenting food during digestion (METHANOGENS)
• agriculture (animal husbandry - cows, and crops - rice)
• energy (processing petroleum)

Question 7

What is permafrost?

Answer 7

Soil that has remained frozen for > 2 years.

Question 8

How does permafrost affect atmospheric methane levels?

Answer 8

When when organic matter becomes frozen in permafrost before it can’t fully decompose aerobically, it decomposes anaerobically into CH4. This methane becomes trapped in the ice and as temps rise, this methane releases into the atmosphere.

Question 9

What is the feedback loop between melting permafrost and global temperatures.

Answer 9

As permafrost melts, CH4 is released into the atmosphere. This GHG causes global warming, which melts the permafrost even more.
POSITIVE FEEDBACK

Question 10

How is methane removed from the atmosphere?

Answer 10

Reactions with hydroxide ions in the atmosphere.

Question 11

How is nitrous oxide produced and removed?

Answer 11

• Produced by bacteria in the soil or lightning separating N3 bonds in the atmosphere.
• Byproduct of agriculture from fertilizers
• Removed from atmosphere by bacteria and UV radiation