1.5 - Feedback Cycles

Question 1

How much solar radiation is absorbed by the Earth?

Answer 1

• 69%
  
  • 50% at Earth’s surface, rest reradiated, but trapped between surface and clouds
• remaining 31% is reflected back by clouds

Question 2

What does affect does increasing vegetation have on absorption of solar radiation?

Answer 2

• increases as vegetation is usually a dark green colour
  
  • thus absorbs more radiation than it reflects

Question 3

What affect does greater cloud coverage have on absorption of solar radiation?

Answer 3

• reduced as clouds reflect radiation away from Earth
  
  • increases reflection, reduces absorption

Question 4

How has natural carbon release varied across the years?

Answer 4

• In Pleistocene/Ice Age, summers were cooler
  
  • resulted in carbon cycle being slower
• However, since then temperature has been rising
  
  • warmer summers mean increased phytoplankton growth
  • more photosynthesis
  • more sequestration of CO₂
  • less carbon in atmosphere —> less warming

Question 5

What is the negative feedback cycle that has interacted with the carbon cycle over time?

Answer 5

Initial Change:
- tree leaf fossils in Arctic show that plants and animals had to migrate towards poles
- as temperatures increased
Reaction to change:
- tectonic folding resulted in mountains being formed
- exposed layers of carbonate rock to weathering processes
- carbon introduced into slow cycle
- carbon solution flows into sea, absorbed by phytoplankton
- die, sink, store carbon away in rock store —> carbon sequestration
- resulted in cooling of planet as less GHG in atmosphere

Question 6

What is the positive feedback cycle that has interacted with the carbon cycle over time?

Answer 6

• Initial change: melting of ice and snow results in lower albedo
  
  • more surface absorption of radiation, LW radiation is trapped within atmosphere
  • temperatures are higher
• 2^nd change: permafrost melts, methane released, more LW radiation trapped, results in even higher temps
• 3^rd change: microbe activity increases within permafrost
  
  • decomposes more material, results in more methane and nitrogen oxides being released

Question 7

How much organic matter is stored in the Siberia permafrost?

Answer 7

• 1700bn tonnes
  
  • stores 4x the amount of carbon it releases into the atmosphere

Question 8

When will the Siberian permafrost thaw?

Answer 8

• When global temperatures rise by 1.5ºC