Lecture 11 Flashcards
Why is water vapour not seen as a problem in the atmosphere?
- despite being most important greenhouse gas
- condensible gas
- concentration variable
- determined by temperature
- So water vapour responds to temperature change rather than controlling it
- thought of as a feedback mechanism
What is the keeling curve?
The curve of CO2 concentration over time
- measured in Mauna Loa Observatory - good as far from point sources of CO2 from human activity and at high elevation
How do we know greenhouse gas concentration in periods before direct measurement?
- fossil air trapped in ice cores in antarctica
- snow has high porosity and so spaces between crystals filled with air
- as snow accumulates the porosity decreases and density increases by compaction from weight
- pores gradually pinched off and form bubbles of air trapped in the ice
How much has CO2 concentration increased since industrial revolution? - mid 18th century
135ppm so by 46%
- CH4 has doubled and N2O has increased by 24%
- CFCs introduced
Relative forcing of the greenhouse gases
- CO2
- CH4
- N2O
- why are these not completely accurate?
- 2.1 Wm^-2
- 0.6
- 0.22
- Simplified as, due to the overlapping of spectral overlap, the changes in one greenhouse gas may affect radiative forcing of others
- Since industrial revolution the radiative forcing is just over 3 Wm^-2
Positive radiative forcing from greenhouse gases are not only anthropogenic effect on the radiation balance
- what are the negative affects and how much?
roughly -1.1
- aerosols and precursors
- NOx
- cloud adjustments from aerosols
- albedo change due to land use
Overall anthropogenic radiative forcing relative to 1750
2.3 Wm^-2
from 2011 study
Climate sensitivity = λ
- getting it from energy balance
Egb = ε(sigma)T^4
take derivative with respect to T
= 4εςT^3
λ= 1/derivative
= K/(Wm^-2)
= Planck sensitivity
= 0.3 is expected warming for every Wm^-2 of radiative energy earth gained or lost by earth
- IGNORES POSSIBLE FEEDBACK SYSTMES
Use Planck sensitivity (λ) to estimate temperature change from anthropogenic forcing
ΔT = λ ΔF
= 0.69K
What is the observed increase in temperature since industrial revolution?
roughly 1 degree celcius
What do graphs that record earths average temperature show?
All months have experienced warming
ΔT is the sum of the steady-state temperature changes (ΔTs, Planck Sensitivity) and feedbacks (ΔΤ feedbacks)
ΔΤ = ΔΤs + ΔΤfeedbacks
- climate feedback mechanisms operate on different time scales and so can be fast (<100yrs) or slow (>100yrs) so feedbacks split
What is the classic definition of climate sensitivity?
the amount of temperature change expected from a doubling of atmospheric CO2 concentrations
no feedback = 1.1 celcius
what are fast feedback systems?
x 4
- sea surface temperature
- Water vapour
- Clouds
- Sea ice
What are slow feedback systems?
x 3
- ice sheets
- Chemical weathering
- Deep ocean temperature
