Atmospheric Greenhouse Gas

Levels

Estimated global warming potentials relative to CO2

Gas Lifetime (years)Warming effect for durations of:

20 years 100 years

Carbon Dioxide (CO2) 5 to 200a 1 1

Methane (CH4) 12 62 23

Nitrous Oxide (N2O) 114 275 296

Some halocarbons (produced only by humans)HFC-23 260 9,400 12,000

HFC-125 29 5,900 3,400

HFC-134a 13.8 3,300 1,300

CF4 50,000 3,900 5,700

C2F6 10,000 8,000 11,900

SF6 3,200 22,200 32,400

(Warming effect = kilograms of CO2 per kilogram of gas)

a No single lifetime can be defined for CO2 due to different rates of uptake by different removal processes.

Note: The uncertainty in the global warming potentials is typically about 35%.

Global CO2 Budgets (billion metric tons/year)

Process 1980 - 1989 1990 - 1999

Atmospheric Increase 12.2 ± 0.37 11.73 ± 0.37

Fossil Fuel Emissions Increase 19.8 ± 1.1 23.1 ± 1.47

Ocean-atmosphere Uptake −6.23 ± 2.2 −8.8 ± 2.57

Land-atmosphere Uptake −1.47 ± 2.57 −2.57 ± 2.93

Land Use Change 7.33 ± 2.93 8.07 ± 2.93

Atmospheric Residence Time for a Pulse of CO2

Greenhouse Gases for the Past 650,000 Years

Measured Increase in CO2, Nitrous Oxide, Methane and CFC’s Since 1979

Methane Beginning to Increase After 8 Years of Stability

• From 1999 to 2006 (8 years) the methane abundance has been relatively stable due to industrial changes in Russia, changes in the methods of rice farming, and methane capture from landfill sites.

• In 2007 the world methane abundance began to increase.• Based on carbon isotope analyses the methane is of biogenic origin.• The source is probably the release from melting permafrost, and the Siberian Arctic

continental slope methane hydrates.• We may now be entering a non-linear climate response.