Temperature K

flG. 11.5. Variation of the global mean vertical atmospheric temperature with increasing atmospheric carbon dioxide levels (1 PAL = 365 ppmv). The RC model has fixed cloud cover of 0.5, surface relative humidity of 0.8, and surface albedo of 0.1. Water vapour and moist lapse rate feedbacks are included, as are changes to atmospheric composition through the inclusion of the photochemistry.

Table 11.3 Climatic effects of increasing atmospheric CO2 levels (1, 2, 4 and 8 PAL), without feedbacks. Water-vapour column, WH2o in g cm"2. Stratospheric peak water-vapour mixing ratio H2O St in ppmv.

parameter

1

2

4

8

Ts

288.15

289.43

290.90

292.50

WH2 o

2.09

2.35

2.65

3.02

h2o St

5.75

5.43

4.79

3.19

troposphere-stratosphere cold trap (temperature minimum) rises in altitude as the stratosphere cools, and so the stratosphere becomes drier. cloud and relative humidity will also play a significant role in controlling the earth's mean global surface temperature.

11.3.5 Climatic effects of increasing CH4 levels

In ยง7.9.2 we saw that the methane mixing ratio increases non-linearly with the surface emission rate of methane. results from an rc-photochemical model,

Table 11.4 Climatic effects of increasing atmospheric CH4 emission (1, 1.2, 1.4, 1.6, 1.8 and 2 PR), where 1 PR = 1080 Tg year-1. Wa,ter-va,pour column Wh2o is in g cm-2. Stratospheric peak water-vapour mixing ratio H2O St is in ppmvv.

parameter

1

1.2

1.4

1.6

1.8

2.0

ch4

1.71

2.49

3.48

4.74

6.27

8.10

co

0.101

0.123

0.149

0.179

0.212

0.249

H2

0.539

0.653

0.771

0.892

1.011

1.128

Ts

288.15

288.32

288.51

288.70

288.90

289.11

WH2 o

2.06

2.09

2.13

2.16

2.20

2.24

h2o St

5.75

6.88

8.45

10.45

12.75

15.50

Table 11.5 Climatic effects of increasing atmospheric CO emission (1.0, 1.5, 2.0, 3.0 PR), where 1 PR = 3295 Tg year-1. Water vapour column WH2O is in g cm-2. Stratospheric peak water-vapour mixing ratio H2O St is in ppmv.

parameter

1.0

1.5

2.0

3.0

co

0.101

0.173

0.273

0.620

ch4

1.71

2.25

2.95

5.16

H2

0.539

0.612

0.673

0.765

Ts

288.15

288.29

288.44

288.82

WH20

2.06

2.13

2.15

2.23

h2o St

5.75

6.80

8.13

12.21

without feedbacks, are given in Table 11.4 for increasing values of methane emission up to twice a present rate 1 pr = 1080 Tg year-1. The global mean surface temperature rise is about 1 K for a doubling in the methane emission rate which results in a methane mixing ratio that is almost 5 times the present mixing ratio. We note that a doubling of the methane mixing ratio results in about 0.4 K rise in the mean global surface temperature. As tropospheric methane levels increase, there is an increase in tropospheric co and H2, due to a reduction in oH by methane. on the other hand, increased oxidation of methane in the stratosphere results in higher water-vapour mixing ratios there.

11.3.6 Climatic effects of increasing CO levels results from an rc-photochemical model, without feedbacks, are given in Table 11.5 for increasing values of co emission up to three times a present rate 1 pr = 3295 Tg year-1. The global mean surface temperature rise is about 0.29 K for a doubling in the co emission rate that results in a co mixing ratio that is 2.7 times the present mixing ratio. As tropospheric co levels increase, reaction with oH increases and so there is a reduction in methane oxidation by oH in the troposphere, thus methane levels rise and so does stratospheric water vapour.

Table 11.6 Climatic effects of increasing atmospheric H2 emission (1.0, 1.5, 2.0, 3.0 PR), where 1 PR = 47 Tg year-1. Wa,ter-va,pour column Wh2o is in g cm-2. Stratospheric peak water vapour-mixing ratio H2 O St is in ppmv.

parameter

1.0

1.5

2.0

3.0

h2

0.539

0.682

0.827

1.123

ch4

1.71

1.75

1.80

1.88

co

0.101

0.103

0.105

0.109

Ts

288.15

288.16

288.17

288.20

WH2 o

2.06

2.10

2.10

2.11

h2o St

5.75

5.93

6.13

6.51

11.3.7 Climatic effects of increasing H2 levels results from an rc-photochemical model, without feedbacks, are given in Table 11.6 for increasing values of H2 emission up to three times a present rate 1 pr = 47 Tg year-1. The global mean surface temperature rise is about 0.02 K for a doubling in the H2 emission rate that results in a H2 mixing ratio that is 1.5 times the present mixing ratio.

11.3.8 Climatic effects of cloud-cover feedbacks

In Table 11.7 are shown the climatic effects of increasing the global cloud cover, for co2 at 1 pAL with the surface albedo fixed at 0.1. The global mean surface temperature decreases as the cloud cover increases and the mean global planetary albedo rises. We see that about 10% increase in cloud cover results in about 2 K global cooling. Methane, co and H2 increase as the water vapour in the atmosphere, and hence oxidation by oH, decreases. The rise in methane partly offsets the global cooling. If cloud cover increases with global warming due to a rise in greenhouse gas concentrations, any rise in temperature would be limited in part by the cloud-cover increase. cloud feedbacks are complex not only because of the uncertainty in the magnitude change in cloud cover brought on by rising levels of greenhouse gases but also uncertainties in the changes in cloud optical properties and cloud types (see chapter 8).

Was this article helpful?

0 0
Guide to Alternative Fuels

Guide to Alternative Fuels

Your Alternative Fuel Solution for Saving Money, Reducing Oil Dependency, and Helping the Planet. Ethanol is an alternative to gasoline. The use of ethanol has been demonstrated to reduce greenhouse emissions slightly as compared to gasoline. Through this ebook, you are going to learn what you will need to know why choosing an alternative fuel may benefit you and your future.

Get My Free Ebook


Post a comment