1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Feedback loops

  1. Oct 18, 2015 #1
    1. The problem statement, all variables and given/known data
    I am just wondering if my analysis of the following feedback loops are right.

    The invariant in this case is Temperature
    Solar heating->Temperature->Evaporation cloud cover-> albedo->Solar heating

    Second feedback loop

    Invariant forest area
    Forest area->Plant evapotranspiration and raincloud->rainfall->forest area

    2. Relevant equations

    3. The attempt at a solution

    Temperature->evaporation cloud cover, it would be a positive coupling hence if more temperature, then more evaporation and cloud cover

    Evaporation cloud cover-> albedo, Evaporation is a greenhouse gas , but at the same time it helps clouds form, so I will go with the greenhouse gas trait because evaporation is one of the causes of greenhouse gases. The coupling would be negative

    Albedo->solar heating, if the albedo decreases then there would be more solar heating coming to the earth
    , so it would be a negative coupling.

    solar heating-> Temperature, positive coupling because if more solar heating coming to the earth then more temperature

    Generally it would be a a positive feedback loop

    second feedback loop

    Forest area-> plant evapotranspiration and raincloud, if the forest area increases then there would be more plants evapotranspirating and more raincloud

    Plant evapotranspiration->rainfall, if there is more evapotranspiration and rain cloud then there would be more rainfall hence the vapor condenses and then it produces rainfall

    rainfall->Forest Area, this one is tricky, assuming that the process is giving naturally then rainfall will help the forest area to protect from sunlight, so it would be positive coupling

    generally it would a positive feedback loop
  2. jcsd
  3. Oct 20, 2015 #2


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    I think the first loop would be negative, because it has albedo as a link. To the extent that evaporation creates clouds, that increases albedo and - other things equal (which they won't be) - reduces solar heating.

    The thing that at least partially offsets this is a different loop, with positive feedback, which is of the form:

    Solar heating->Temperature->Evaporation-> Increased water vapour in non-cloud covered areas->Solar heating

    In this case the water vapour acts purely as a greenhouse gas, which increases heating, because in those areas it has not formed clouds and hence does not generate the white surface needed for albedo.

    Of course neither of these water-vapour-focused loops deal with the really important greenhouse gas CO2, which has other feedback loops (eg melting of permafrost releasing ground-stored CO2 into the atmosphere).
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted