// lecture 08

Question 1

climate forcings

Answer 1

things that change global temperatures directly.

Question 2

climate feedbacks

Answer 2

things that respond to temp changes, but themselves affect temp too. change in response to a climate forcing.

• ice/snow - ice melts when it gets hotter.
• water vapor and clouds too.

Question 3

examples of climate forcings:

Answer 3

changes in strength of the sun, changes in GHG concentrations, and volcanoes (which block out the sun).

Question 4

radiative forcing

Answer 4

calculated as the change in shortwave in or longwave out due to the particular climate forcing. measured in W/m^-2.

Question 5

positive radiative forcing

Answer 5

n increase in shortwave radiation absorbed by earth or a decrease in longwave out of earth. climate must warm in response to a positive radiative forcing.

Question 6

radiative forcing for GHGs

Answer 6

instantly change the gas concentration as compared with a reference concentration.

Question 7

current values of radiative forcings for:

Answer 7

CO2: 1.66 W/m^2, methane: 0.48 W/m^2, nitrous oxide: 0.16 W/m^2, and CFCs: 0.32 W/m^2.

Question 8

examples of shortwave forcings:

Answer 8

changes in strength of sun, changes in surface albedo, volcanoes, and air pollution.

Question 9

sun has natural variability in its strength

Answer 9

0.1% change. variability is correlated with the sunspot cycle.

Question 10

sunspots

Answer 10

temporarily darkened regions on the sun. vary over 11 yr. cycle. more sunspots -> more solar radiation. also more solar flares during solar cycles. not the same each 11 yr cycle.

Question 11

aerosols

Answer 11

fine particles suspended in the air; make a large contribution to reflection of sunlight. includes volcanoes, pollution, dust, etc.

Question 12

direct heating of atmosphere by

Answer 12

volcanoes is small.

Question 13

CO2 emission by volcanoes is

Answer 13

21% of anthropogenic emission.

Question 14

Krakatoa eruption (1883)

Answer 14

one of the biggest and deadliest eruptions in history. Indonesian Island east of Java mostly disappears. in the following year, summertime temps. in N. hemisphere fell by 1.2 C. very explosive with sulfur in gases.

Question 15

volcano impacts on climate:

Answer 15

• dust and sulfates from volcanoes block out the sun.
• volcanic material spreads quickly around the same latitudes as the eruption.
• slight dimming seen across the globe.

Question 16

air pollution particles

Answer 16

block out the sun too. sulfate aerosols are sulfates directly from dirty coal burning.

Question 17

aerosol haze

Answer 17

reflect sunlight back to space and cool. they fall out over a few days.

Question 18

radiative forcings for shortwave agents in current climate vs preindustrial:

Answer 18

CO2 1.66 W/m^2, solar radiation changes 0.12 W/m^2, land cover changes -0.20 W/m^2, soot on snow 0.10 W/m^2, aerosol direct effect -0.50 W/m^2, aerosol indirect effect (clouds) -0.70 W/m^2.

Question 19

total radiative forcing

Answer 19

1.6 W/m^2

Question 20

land cover changes

Answer 20

• forests have low albedo
• cutting down forests to create farmland/pastures tend to raise the albedo (neg. radiative forcing, causes local cooling because there’s more solar energy reflected)
• but causes global warming because it releases CO2

Question 21

Global dimming

Answer 21

• solar radiation reaching the Earth’s surface declined by 4% from 1961-1990
• increased aerosol concentrations partially to blame (both direct reflection and indirect cloud changes are thought to be important)
• trend has reduced since 1990s most likely to Clean Air Act

Question 22

aerosol effects on climate

Answer 22

sulfate aerosols reflect away sunlight, causing cooling so cleaning up air pollution has increased air quality etc. but has most likely caused warming