Kangaroo farts and global warming

Jim Addison of Wizbang wrote in Kangaroo farts could ease global warming citing Herald Sun:

AUSTRALIAN scientists are trying to give kangaroo-style stomachs to cattle and sheep in a bid to cut the emission of greenhouse gases blamed for global warming, researchers say. Thanks to special bacteria in their stomachs, kangaroo flatulence contains no methane and scientists want to transfer that bacteria to cattle and sheep who emit large quantities of the harmful gas.

One of Jim's reader left a comment pointing out that the main conern we should focus on is CO₂:

However, methane is the "greenhouse gas" which does the most damage - equivalent to roughly twenty times an equal volume of CO₂.

Nice try, methane is more potent but it doesn't "do the most damage" in terms of radiative forcing (RF) because there is so much less of it.

CO₂ levels are about 380 ppm and methane levels are 1.75 ppm. Even with it's much higher potency it only contributes about 28% the RF of CO₂.

Furthermore CO₂ has much higher atmospheric lifetime than methane. Methane's AL is about 9-15 years, while CO₂'s AL is thousands, if not tens of thousands, of years.

This is not to say that methane emissions should be ignored, especially regarding their contribution to positive feedback loops. However methane emissions have been decreasing since the early nineties and have even leveled off since 2000, while CO₂ emissions keep increasing. Such studies as the one linked above could lead to very useful reductions in methane emissions, but they aren't going to be anywhere near enough to offset that of CO₂.

I did a little research and found this:

Water vapour

Water vapour is the most important greenhouse gas, but human activity has little direct impact on the amount in the atmosphere.
Carbon dioxide (CO₂)

The amount of carbon dioxide in the atmosphere is about 30% higher now than 200 years ago. The main causes of this increase are:

* the burning of fossil fuels such as oil, coal and natural gas to create energy to make electricity and to produce fuel for transport, and
* the clearing and burning of vegetation.

This gas is the biggest contributor to the enhanced greenhouse effect (about 70%)

Methane (CH₄)

The amount of methane in the atmosphere is about 145% higher now than 200 years ago. The main causes of this increase are:

* digestive processes of cattle and sheep (ie their burps!)
* cultivation of rice
* escape of natural gas
* decomposing waste in garbage dumps or landfills.

This gas is the second biggest contributor to the enhanced greenhouse effect (about 20%)

Nitrous oxide (N₂O)

The amount of nitrous oxide in the atmosphere is about 15% higher now than 200 years ago. The main causes of this increase are:

* burning of vegetation
* emissions from industries
* the effects of agriculture on the soil (using nitrogenous fertilisers)

Halocarbons

These greenhouse gases have been reduced since the phasing out of chlorofluorocarbons (CFCs) to protect the ozone layer. However, other halocarbons effecting the atmosphere include perfluorocarbons (PFCs) emitted during aluminium production.

Anyway, I will give Jim the last words. "Improving feed efficiency by 10-15% would by itself be a revolutionary breakthrough, lowering food costs and helping the economy as well as the environment, even without the benefits of reduced methane."