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ENGR202 > Midterm - > Final > Flashcards

Midterm - > Final Flashcards

1
Q

What is radiative forcing?

A

change in average net radiation considered at the top of the troposphere (known as the tropopause) due to change in either solar or infrared radiation (from Earth)

Perturbs the balance between incoming and outgoing radiation.

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2
Q

What would be a positive radiative forcing?

A
  • (+)ve radiative forcing -> warm the surface

* (‐) ve radiative forcing -> cool the surface.

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3
Q

What kind of radiative forcing would an increase in CO2 concentration be?

A

Positive radiative forcing

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4
Q

What would doubling the pre-industrial CO2 concentration entail? Radiative Forcing, Troposphere temp?

A

Global mean radiative forcing: ~ 4 W/m^2

Increase temp. at troposphere and of the surface

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5
Q

What are the overall positive radiative forcings for all GHGs?

A

Absorbing outgoing IR radiation.

CO2:
- Largest increase in forcing over the period.
O3:
- Positive forcing for tropospheric Ozone.
- Negative forcing for stratospheric Ozone.

Aerosols:

  • Negative direct radiative forcing
  • Negative radiative forcing: cause of changes in cloud properties.
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6
Q

How does the Albedo affect the positive or negative radiative forcing?

A

Net negative radiative forcing due to increased reflection of solar radiation from Earth’s surface (albedo)

  • Negative: Altered nature of land cover (changes in croplands, pastures and forests)
  • Positive: Altered reflective properties of ice and snow (black carbon on snow)
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7
Q

What are contrails and how do they affect Albedo?

A

Contrails are linear trails of condensation by aircrafts

  • They reflect solar radiation
  • They absorb IR radiation
  • Global aircraft operations -> Increased cloudiness -> little positive radiative forcing
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8
Q

Name some important GHGs

A

C02, 03, Aerosols, CH4, N2O, CFCs and other halocarbons

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9
Q

What are the minor atmospheric constituents?

A
  • Nitrogen Oxides (NOx) and carbon monoxide (CO) (not important greenhouse gases on their own) may influence some greenhouse gas concentration. (e.g. tropospheric ozone) through atmospheric chemistry: INDIRECT RADIATIVE FORCINGS
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10
Q

Where do Aerosols in the troposphere come from?

A

Oxidation of sulphur dioxide and from biomass burning.

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11
Q

How do Aerosols in the troposphere affect the albedo?

A

They change the reflection and absorption of solar radiation.

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12
Q

What is the indirect radiative forcing effect caused by the Aerosols in the troposphere?

A

Indirect radiative forcing effect: result from the influence of aerosols on the size of cloud droplets, and hence on cloud reflectivity.

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13
Q

What is the NET radiative forcing caused by Aerosols in the troposphere?

A

It is a net negative forcing (cooling the surface)

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14
Q

What are some other radiative effects caused by aerosols?

A

1- Scattering of radiation
- By reflection, refraction, or diffraction of the radiation beam.
2- Visibility reduction:
- The visibility of an object is determined by its contrast with the background. This contrast is reduced by aerosol scattering of solar radiation into the line of sight and by scattering of radiation from the object out of the line of sight.

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15
Q

Describe the model that estimates the climatic effect of a scattering aerosol layer of optical depth. Radiative forcing from the anthropogenic aerosol layer.

A 
Delta F = ( -Fs A* (1-Ao)^2 ) / 4
Where A* = Fu/Fs = 5x10^-3
Where Ao = Earth's Albedo
Delta F in this case is -0.9 W / m^2
https://i.imgur.com/3qQANFi.png
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16
Q

What is the approximate direct forcing from aerosols?

A

~ - 0.5 W / m^2 (IPCC estimate)

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17
Q

Give examples of direct positive radiation and negative radiation forcing.

A

Negative Radiation forcing:

  • Sulfate particles (combustion of coal and oil)
  • Aerosol particles from combustion of biomass (wood, paper, agricultural waste)

Positive:
- Soot particles with high carbon content: absorb solar radiation.

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18
Q

What region is more affected by the Net negative radiation forcing?

A

The northern hemisphere tends to be the area more affected due to the high concentration of fossil fuel combustion and related activities are intense.

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19
Q

What are some indirect forcing from aerosols?

A
  • Microscopic aerosol particles acting as condensation nuclei for cloud formation -> cloud albedo effect: negative radiative forcing
    (-0.7 W/m^2 with large uncertainty)
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20
Q

What is the most important greenhouse gas apart from CO2 ?

A

Water vapour, from mostly oceans

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21
Q

How much does humans impact the perturbation of water vapour?

A

Negligible

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22
Q

How strong are the indirect feedbacks of global warming and greenhouse gasses that affect water vapour?

A

Very strong.

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23
Q

How does the indirect feedbacks of greenhouse gasses affect water vapour?

A

Increase GHGs -> Increase in surface temp -> increase in evaporation of water from ocean - > Enhanced global warming

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24
Q

What is the runaway greenhouse effect?

A

total evaporation of ocean and high surface temp

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25
Q

Compare Earth to Venus on the runaway greenhouse effect

A

Earth: Saturation water vapour pressure of water was eventually reached -> condensation and precipitation

Venus: Never reached the saturation -> continuous accumulation of water vapour in the atmosphere: the runaway greenhouse effect.

NOTE: distance from the sun prevented the runaway greenhouse effect to occur on the Earth.

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26
Q

Name and describe some Radiative forcing from Natural changes.

A

Solar changes:

  • 0.3 W/m^2 with an uncertainty of +- 67%
  • small positive radiative forcing (Increased gradually in the industrial era)
  • Cyclic changes (11-year cycle)

Volcanic eruptions:

  • Positive forcing with short duration (2 to 3 years)
  • increase of sulphate aerosol in the stratosphere
  • currently free of volcanic aerosol
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27
Q

What is the Radiative forcing from natural occurrences vs human activities?

A

RF in solar irradiance changes and volcanoes (0.3w/m^2) vs human activities (2.63W/m^2)

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28
Q

What is the formula for radiative forcing?

A

Delta F = Delta q(out) - Delta q(in)

where,
delta q(out) = (W/m^2 outgoing initially) - (W/m^2 outgoing after perturbation)

delta q(in) = (W/m^2 incoming initially) - ( W/m^2 incoming after perturbation)

29
Q

Example: Radiative forcing from Co2 addition:

Increase in atm CO2 concentration -> Reduced outgoing IR radiation at tropopause from 235 W/m^2 to 233 W/m^2. No change in solar radiation and albedo. What is the radiative forcing delta F?

A

No change in incoming radiation -> delta q(in) = 0

delta q(out) = 235 -233 = 2W/m^2
delta F = delta q(out) - delta q(in) = 2 - 0 = 2 W/m^2
30
Q

What is the formula for the change in outgoing terrestrial energy?

A

delta q(out) = (W/m^2 outgoing initially) - (W/m^2 outgoing after perturbation)

31
Q

What is the formula for the change in incoming solar energy?

A

delta q(in) = (W/m^2 incoming initially) - ( W/m^2 incoming after perturbation)

32
Q

Example: Radiative forcing from a sulfate aerosol:

Increase in sulfate -> increase albedo -> add 0.5 W/m^2 to reflection by tropopause

A

delta q(out) = x (W/m^2 initially) - (x+0.5) (W/m^2 after perturbation) = -0.5 W/m^2

delta q(in) = 0
delta F = delta q(out) - delta q(in) = -0.5 - 0 = -0.5 W/m^2
33
Q

What is the radioactive forcing formula for CO2?

A

delta F = (alpha)( ln( C/Co ) ) ,

where alpha = 5.35

where C is the CO2 in ppm
the subscript ‘o’ denotes the unperturbed molar fraction for the species being evaluated.

34
Q

What is the radioactive forcing for CH4 and N2O?

A

Where
M is CH4 in ppb
N is N2O in ppb
the subscript ‘o’ denotes the unperturbed molar fraction for the species being evaluated.

35
Q

What is the difference between Radiative forcing vs concentration? (low concentration regime)

A

radiative forcing = f(initial concentration of GHGs in atm)

Delta F = A( C - Co )

36
Q

What are some properties that affect the radiative forcing?

A
  • Radiative sorption characteristics of the gas,
  • the thickness and temperature profile of the atmosphere,
  • Effects of clouds and present other radiative gases
37
Q

What factors indirectly affect the radiative forcing?

A
  • presence of other energy-absorbing gases

- any changes in the stratosphere

38
Q

What is the difference between Radiative forcing vs concentration? (moderate concentration regime)

A

delta F = B( sqrt( C ) - sqrt( Co ) )

  • molecules already in the atmosphere absorb much of the radiation at the wavelength where absorption bands are strong
  • Further absorption occurs increasingly at “off-peak” wavelengths, where absorptivity (alpha A) is lower
39
Q

What is a spectral overlap?

A

absorption bands of multiple gases overlap -> radiative function becomes dependent

40
Q

What is the difference between Radiative forcing vs concentration? (High concentration regime)

A

delta F = k ( ln( C ) - ln ( Co ) )

for Co2, k = 6.3

The concentration of Greenhouse gasses high level - > increase of C -> much smaller increase in RF

41
Q

Examples:
Radiative forcing from CFC-12:

By 1992, the atm concentration of CFC-12 reached 500 pptv from initial value of zero. Calculate the change in direct radiative forcing.

A

CFC-12:
delta F = 0.28( Y - Yo )
Co = 0.0 , 500 pptv = 0.5 ppbv
delta F = 0.28 (0.5 - 0) = 0.14 W/m^2

42
Q

Radiative forcing from CO2:

Estimate delta F from a doubling of the 1992 Co2 concentration of 355 ppmv.

A

Carbon Dioxide: delta F = 6.3 ( ln( C/Co ) )

delta F = 6.3 ( ln( 2 ) ) = 4.37 W/m^2

43
Q

Example: Equivalent CO2 increase since pre-industrial times: (Pre-industrial concentration of CO2 in atm 280 ppmv)

In 1992, an increase in CO2, CH4, N2O and halocarbons have produced a direct radiative forcing totalling 2.45 W/m^2. What is the equivalent CO2 concentration needed to produce the forcing?

A

FORMULAS USED:

delta F(total) = 6.3 ln( C(equiv) / Co )

C(equiv) (ppmv CO2) = Co (delta F(total) / 6.3 ) = 280 ^(2.45/6.3) = 413 ppmv CO2

This represents a 48% increase over the initial preindustrial CO2 level (=280 ppmv)

Actual CO2 concentration in 1992 = 355 ppmv ( =27% increase )

Actual Co2 concentration ( CH4, N2O, and halocarbons) is responsible for the additional 21% increase (=48%-27%)

44
Q

What is the equation for the climate sensitivity factor(y)?

A

y = delta t e / delta F rad

delta t e = y(delta F rad)

45
Q

How can you determine the climate sensitivity from a graph?

A

https://i.imgur.com/YNMRrCD.png

46
Q

What are GCMs?

A

GCMs = General Circulation Models

  • 3D computational Fluid Dynamics model
  • Unsteady
47
Q

What are the inputs, outputs of a GCM?

A

Inputs:
- Solar radiation, GHGs and aerosols, land-use parameters, topography, volcanic activity and initial temps ( temp, winds data, pressure, salinity in ocean, currents, sea-ice)

Middle:
-> Coupling models

Outputs:

  • > Present-day climate (hindcasts)
  • > future climate (projection, prediction)
  • > climate of the past (paleoclimate)
48
Q

What are time lags?

A 
The time required to reach a new equilibrium. 
delta t (lag) = teq - t
delta T(commit) = Teq(t) - Te(t)
49
Q

Q1: Radiative forcing from a doubling of the current CO2 concentration was estimated to be 4.37 W/m^2. What is the resulting increase in equilibrium surface temperature if the climate sensitivity factor is 0.6 °C/Wm^2?

A

delta Te = y(delta F rad) = 0.6 * 4.37 = 2.6°C

50
Q

Q2: Use the IPCC values of 1.5°C, 2.5°C and 4.5°C for the low, best, high estimates of equilibrium temperature change from a CO2 doubling to calculate the implied values of the climate sensitivity factor, y (CO2 concentration was estimated to be 4.37 W/m^2)

A

IPCC ESTIMATE - > LOW - > BEST -> HIGH
delta t 2X -> 1.5 - > 2.5 -> 4.5
y°C -> 0.34 -> 0.57 -> 1.03

y = delta t 2x / 4.37

51
Q

Q3: A climate model assumes a 1% / yr increase in CO2 concentration doubling CO2 after 70 years. At that time the realized increase in surface temperature is 62% of the equilibrium value. The equilibrium for a CO2 doubling ( delta t2x ) is 2.5. What are the actual surface temp. after 70 years and temperature commitment at that time?

A

delta te = 0.62 * 2.5 = 1.6 °C
delta t commit = Teq(t) -Te(t) = 2.5 - 1.6 = 0.9 °C
if further increase of CO2 stops after 70 years, the surface temperature will still continue to go up by 0.9 °C.

Formulas used:
delta t lag = t eq - t
delta T commit = Teq(t) - Te(t)

52
Q

Define time lag and temperature commitment from a graph.

A

https://i.imgur.com/hyw1EFI.png

53
Q

What is the wide range of predicted CO2 emission? What is their names and their multiplier from 1990 level?

A

IS92a : 3x
IS92e: 8x
IS92c: gradual decline

https://i.imgur.com/MXx0yV3.png

54
Q

What is the Atmospheric Lifetime tow(t) of GHGs? (what is the formula)

A

dm / dt = -B m
m = mo e^( -Bt )
(atmospheric lifetime): tow = 1 / B
Therefore, m = mo e^( -t / tow )

Where,

dm/dt is your instant rate of change.
B is the proportional constant
m is the mass remaining at any time t.

55
Q

Example: CH4’s atmospheric lifetime tow is 12 years. 1Kg of Ch4 is added to atmosphere today. How much will be remaining after 1 yr?

A 
mo = 1.0kg 
tow = 12 years
tow = 1 / B
using formula: m = mo e^( -Bt )
m = 1.0 e ^ ( -1/12 ) = 0.92 kg (8% loss /year)
  • Therefore, No more than 8% of initial CH4 into the air to maintain the current level
  • Halocarbons and perhalogens: long lifetime (tow) -> stabilization requires complete elimination of emission
56
Q

What is the formula for the simple carbon cycle model using 2 decay rates?

A

mC / M C,o = 0.375 e^( - t / 10.43 ) + 0.625 e ^ ( -t / 291.5 )

m c ,o = initial carbon mass
mc = amount remaining after t years

57
Q

Practice Problem:

US CO2 emissions in 1996 were 5.3 Gt. How much CO2 will still be in the atmosphere in year 2100? Assume no further CO2 additions.

A

Using formula mc/ mc,o = 0.375( -t / 10.43 ) + 0.625 e^( -t/291.5 )

mC,o = 1.45 Gt C and delta t = 104 years (2100 - 1996)
mc/mc,o = 0.375 e^( -104/10.43 ) + 0.625 e^( -104/291.5 )
= 0.437

mc = 0.437 mc,o = (0.437)(1.45) = 0.63 Gt C

58
Q

Calculating CO2 emission example: (table given)
https://i.imgur.com/PdeZPmA.png

In 2010, 4700 million metric tons of coal were burned globally. Determine carbon emission rate in unit of Gt C/r and Gt CO2/yr

A

coal mass = 4700 million metro tons -> 4.7 Gt
Carbon content = 59%C
Mass of carbon emission = 4.7 Gt x 0.59 ( Gt C / Gt coal) = 2.8 GtC/yr
CO2 emission = 2.8 x 44/12 = 10 Gt CO2 / year
44/12 corresponds to 1 mass unit C.

59
Q

What is the alternative method of calculating CO2 emissions based on energy content?

A
  • C and H content in fossil fuel -> energy
  • Heating value (kj/kg or kj/mol) = Energy / Unit mass
  • Higher heating value (HHV) = lower heating value (LHV) + heat of vaporization of the water content in the fuel.
    LHV = HHV - 0.212H - 0.0245M - 0.008Y
    H = percent hydrogen, M = percent moisture, Y = percent oxygen
60
Q

What is carbon intensity equal to?

A

Carbon intensity = Carbon content / Energy content = Fraction of C in fuel / Fuel Heating Value

61
Q

Example question:

CH4’s HHV is 55.64 kJ / g. What is the Carbon Intensity?

A

fraction of C = mass of C / Mass of CH4 = 12/16 = 0.75g C / gCH4
Carbon intensity = [0.75 g C / gCH4] / [55.64 kj CH4] = 13.5 g C/Mj

62
Q

What is the mass of carbon emitted equal to?

A

mass of carbon emitted = energy use x carbon intensity

63
Q

Problem:
Natural gas was accounted as 24 % of total energy consumption in US 99.39 x 10^15 kJ this year. Determine Carbon emission from Natural Gas use in unit of Gt C?

A

Energy from natural gas = 0.24 * 99.38 = 23.85 EJ (10^18J)

Carbon emitted = 23.85EJ * 13.7 g C/Mj = 3.3 x 10^14 g C = 0.33 Gt C * 13.7 gC/MJ = 3.3 x 10^14 g C = 0.33 Gt C
from table (13.7 C/MJ for natural gas)
64
Q

How do we calculate Energy usage?

A

Energy use = Population x [ GDP / per capita ] x [ Energy use / per GDP ]

65
Q

How can we reduce the energy use per GDP?

A
  • Structural change
  • High energy-intensity industry
  • Efficiency Improvement
66
Q

How can we reduce Carbon Intensity (CO2 emission per unit energy)?

A
  • Alternate Energy Sources - No carbon emission
  • nuclear power: high capital costs, societal and environmental concerns on safety, the spread of nuclear weapon, radioactive disposal
  • Wind, Solar, Tidal, and Biomass (net zero CO2 emissions): not yet economically competitive.
  • > Policy measures (incentives (carbon TAX), a limit on CO2 emission)
  • Electric cars with battery or fuel cell
  • Carbon sequestration
67
Q

What is carbon sequestration?

A

Capturing carbon dioxide (CO2) stationary sources (power plants) and putting into long-term storage.

  • > terrestrial (or biologic) sequestration: indirect
    • using plants to capture CO2 from the atmosphere and then storing it as carbon in the stems and roots of the plants as well as in the soil.
  • > Geologic sequestration: direct:
    • putting Co2 into long-term storage in geologic zones deep underground
68
Q

What does GWP stand for? what does it mean?

A

Global warming potential (GWP): relative measure of how much heat a greenhouse gas traps in atmosphere.

69
Q

What is the equation for GWP?

A

global warming potential (GWP) = [integral 0 -> Y of delta F GHG * f GHG (t) dt] / [integral 0 -> Y delta F co2 f co2 (t) dt]

where,
delta F GHG : change in the radiative forcing due to 1 kg of gas at t = 0
f GHG : fraction of gas remaining in atmosphere at any time t

ENGR202 (2 decks)

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