Greenhouse warming potential

The greenhouse warming potential (GWP) is used to measure the rate at which greenhouse gases exacerbate the greenhouse effect. The substances subject to restrictions in the Kyoto protocol are rapidly increasing their concentrations in Earth's atmosphere or have a large GWP.

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The GWP depends on the following factors:

• the absorption of infrared radiation by a given species
• the spectral location of its absorbing wavelengths
• the atmospheric lifetime of the species

Thus, a high GWP correlates with a large infrared absorption and a long atmospheric lifetime. The dependence of GWP on the wavelength of absorption is more complicated. The dependence of GWP as a function of wavelength has been found empirically and published as a graph.^[1]

Because the GWP of a greenhouse gas depends directly on its infrared spectrum, the use of infrared spectroscopy to study greenhouse gases is centrally important in the effort to understand the impact of human activities on global climate change.

Calculating the greenhouse warming potential

The radiative forcing capacity (RF) is the amount of energy per unit area per unit time, absorbed by the greenhouse gas, that would otherwise be lost to space. It can be expressed by the formula:

[Math formatting is needed]

RF = {sigma}(n = 1 to 100) Abs_i * F_i / (path length * density)

where the subscript i represents an interval of 10 inverse centimeters. Abs_i represents the integrated infrared absorbance of the sample in that interval, and F_i represents the RF for that interval. Note that RF varies for different intervals.

The GWP is then:

[Math formatting is needed]

GWP = τ_gas * e ^ (-time / τ_gas - 1) * x * RF_gas / MW_gas

all divided by the same calculation for a reference compound, normally CO₂,

where τ is the atmospheric lifetime of the gas in years, and MW is the molecular weight of the gas.

References