365 Days of Climate Awareness 319 – Global Warming Potential – Daily Kos
Global warming potential is treated as a scalar: that is to say, a number without units, because all greenhouse gases are compared to carbon dioxide. CO2, by definition, has a GWP of 1. Since the gases have vastly different lifetimes: carbon dioxide, roughly 120 years, methane roughly 10.4, and CFCs less than that, their warming potential is averaged into a 100-year span. A few principle gases, using this 100-year average, are listed below. (For concentrations: ppm = parts per million; ppb = parts per billion; ppt = parts per trillion.)
Carbon dioxide (CO2): GWP = 1; lifetime ~120 yrs (but can vary widely); 410 ppm
- Methane (CH4): GWP = 28; lifetime = 10.5 yrs; 1,800 ppb
- Nitrous oxide (N2O): GWP = 265; lifetime = 132 yrs; 380 ppb
- Various chlorofluorocarbons (CFCs): 4,660-13,900; lifetimes 16-500 yrs; 1-100 ppt
- Sulfur hexafluoride (SF6): GWP = 23,500; lifetime = 3,200 yrs; 10 ppt
Different time frames (20 years, 200 years) are used by different agencies around the world, but the concept is the same: amount of energy absorbed by a given mass of greenhouse gas during that timEPA – greenhouse gas concentrationse, given the average solar input of roughly 1.366 kW/sq m. With this statistical tool scientists can directly compare the impacts of various gases, though for high-resolution climate modeling, the different gases with their distinct behaviors are accounted for separately.
Tomorrow: introduction to general circulation models.
Be brave, be steadfast, and be well.