Vital Climate Graphics - Update

11

VITAL CLIMATE CHANGE GRAPHICS

The main greenhouse gases

Pre-industrial concentration ( ppmv * )

Concentration in 1998 ( ppmv )

Atmospheric lifetime (years)

Main human activity source

Water vapour is the most abundant green- house gas. However, human activities have little direct impact on its concentration in the atmosphere. In contrast, we have a large im- pact on the concentrations of carbon dioxide, methane and nitrous oxide. In order to be able to compare how different gases contribute to the greenhouse effect, a method has been de- veloped to estimate their global warming po- tentials (GWP). GWPs depend on the capac- ity of greenhouse gas molecules to absorb or trap heat and the time the molecules remain in the atmosphere before being removed or bro- ken down. GWPs can be used to define the impact greenhouse gases will have on global warming over different time periods – usually 20 years, 100 years and 500 years. The GWP of carbon dioxide is 1 (constant for all time periods) and the GWPs of other greenhouse gases are measured relative to it. Even though methane and nitrous oxide have much higher GWPs than carbon dioxide, because their con-

Name

GWP **

-

Water vapour

1 to 3

-

1 to 3

a few days

fossil fuels, cement prod- uction, land use change fossil fuels, rice paddies waste dumps, livestock

Carbon dioxide (CO 2 )

280

1

365

variable

Methane (CH 4 )

0,7

23

1,75

12

Nitrous oxide

fertilizers, combustion industrial processes

0,27

296

0,31

114

(N 2

O

)

HFC 23 (CHF 3 )

0

12 000

0,000014

260

electronics, refrigerants

HFC 152 a (CH 3 CHF 2 ) HFC 134 a (CF 3 CH 2 F )

0

1 300

0,0000075

13,8

refrigerants

0

120

0,0000005

1,4

industrial processes

Perfluoromethane (CF 4 ) Perfluoroethane (C 2 F 6 ) Sulphur hexafluoride (SF 6 )

0,00004

5 700

0,00008

> 50 000

aluminium production

0

11 900

0,000003

10 000

aluminium production

0

22 200

0,0000042

3 200

dielectric fluid

* ppmv = parts per million by volume, ** GWP = Global warming potential (for 100 year time horizon).

United Nations Environment Programme / GRID-Arendal

Increasing air travel means that more of these warming clouds will be produced.

centration in the atmosphere is much lower, carbon dioxide remains the most important greenhouse gas, contributing about 60% to the enhancement of the greenhouse effect (Houghton et al 2001). Cloud makers Clouds can either heat or cool the Earth, depending on their altitude and size. An experiment carried out in the 1980s found that in general clouds tend to cool the planet. If we remove all the clouds from the atmosphere the aver- age temperature is estimated to increase by approximately 11°C (NASA). However, one particular “man made” cloud type is implicated in global warming. Water vapour emit- ted by aircraft, referred to as condensation trails, produc- es high altitude ice clouds. Like cirrus clouds, these cold wispy trails trap heat, effectively warming the atmosphere.

The cooling effect Increasing greenhouse gases in the atmosphere can warm the planet, but other factors can cool it. These include aerosols in the atmosphere, such as volcanic ash, soot, dust and sulphates. Small aerosol particles are very effec- tive at reflecting incoming solar radiation back into space and consequently cooling the Earth. Increasing the area of reflective surfaces can also lead to cooling (referred to as increasing albedo). Deforestation is an example, as the exposed ground is more reflective than the forest canopy. Increasing snow cover acts in the same way, as snow and ice are more reflective than the land or the ocean.