Slicing the greenhouse gas pie: What gases?

We keep talking about the need to reduce the greenhouse gas we produce. But how do these gases get in the atmosphere? To answer that question we need to look at what I like to call the “greenhouse gas pie,” and it turns out there are lots of ways to slice it up.

One way is to slice the pie up by the type of gases we’re talking about. There are dozens of human-produced greenhouse gases, three of them get special attention: carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O). Here’s why.

CO2 is the most important because it causes about 67 percent more warming than all the other greenhouse gases combined. Methane causes less than a third as much warming as CO2, but it is responsible for about three times more warming than nitrous oxide.

Greenhouse gas pie: Sliced by the amount of warming contributed by each human-produced greenhouse gas.

That’s somewhat interesting, but doesn’t do much to show us opportunities to reduce emissions of these gases. What are the principal man-made sources of each gas? That requires us to look at another set of pies.

Let’s first look at CO2 in more detail, since it’s the biggest slice of the pie above. Globally, about 80 percent of CO2 comes from burning fossil fuels like coal, oil and gas. (If you’ve ever wondered why they’re called “fossil” fuels, it’s because they are made from the remains of plants and animals that died hundreds of thousands or millions of years ago – in other words, they are fossils.) The biggest sources of fossil fuel CO2 are coal and petroleum (about 40 to 45 percent each), with natural gas contributing the rest. The other 20 percent of global CO2 is released through deforestation.

Carbon dioxide pie: Sliced by human-produced sources, which are burning fossil fuels and deforestation.

Turning next to methane — worldwide, the major source is agriculture, primarily rice farming and livestock. Methane is a normal digestive byproduct in domesticated animals like cows, sheep and goats. As the EPA diplomatically describes it, the animals “exhale” the gas after digesting their food (it comes out the other end, too). Animals also produce manure, which releases methane as it decays.

Other important methane sources are deforestation, coal mining and the production and distribution of natural gas and oil. In the United States, landfills are the largest source of methane emissions. The good news is that it is relatively easy to capture methane from manure and landfills. Not only does this prevent emission of methane into the atmosphere, the captured methane can also be burned to generate electricity.

Finally, the other major greenhouse gas, nitrous oxide, comes primarily from agricultural soils. The opportunity to reduce emissions here is in more efficient use of fertilizers. Applying fertilizer in a different form, at a different time, or in a different amount can mean more is used by the crops instead of being transformed into nitrous oxide.

Coming up shortly, another pie showing another view of where the greenhouse gases come from.

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  1. donwalkee
    Posted April 28, 2007 at 2:45 pm | Permalink

    Dear Sir,
    I’m just an average guy trying to look at both sides of the global warming issue. My family tries to do our part by recycling and I carpool to work, but when I read your blog about flying airplanes into the upper atmosphere and releasing what amounts to be mirrors to reflect the suns energy as serious alternative seems not only far fetched and just down right silly. Who is going to pay for this? Is the science sound? It seems to me that if you want to be taken seriously you might stay with the basics. Global warming 0. Non believers 1.
    Still trying to believe!

  2. Posted May 1, 2007 at 11:09 am | Permalink

    Hi dwalk,

    In the article I posted about geo-engineering, I said that some ideas have “technical merit” (that is, they do result in cooling), but “it’s premature to contemplate such drastic measures” and “geo-engineering is a risky proposition”. That’s far short of an endorsement! As I pointed out, geo-engineering ignores other damaging effects of greenhouse gases such as ocean acidification.

    The best way to fight global warming is to decrease our greenhouse gas emissions, so kudos to you and your family for doing your part. You can pick up more tips on how to cut emissions (and save money) at

  3. kolibri
    Posted May 4, 2007 at 10:21 am | Permalink

    Dear Sir,

    I have yet to see the scientific evidence that shows a mechanism by which it is possible for such a minute amount of CO2 in the atmosphere to be the cause of global warming. Factors in the generating of heat (mainly though radiation) often ignores the effects of convection in the atmosphere. CO2 emission is regulated by the oceans and increases with an increase in temperature not the other way around. Water and water vapor have a much greater impact on the heat level than does CO2. The oceans release a much higher amount of CO2 than humans do. Satellite and balloon measurements of the earth temperatures show there has been no significant “warming” nor is it taking place to the degree that we are urged to believe. Computer models based on incorrect logic and science can not be a reliable source of projection.
    There are about 160,000 glaciers on Earth, some are expanding, some are decreasing and no more than 100 have been observed over a long period of time. CO2 increases due to increase in temperatures, not the other way around. It is significant to me that the scientific data on which the UN commission based its findings will not be available until about 10 months from now. Add to that the inappropriate term “greenhouse” gases and understanding how a greenhouse actually functions and that the atmosphere is not a greenhouse adds to my suspicions.

    Best regards,

    bernd D Gruner, Germany

  4. Posted May 7, 2007 at 11:17 am | Permalink


    Here are some links that address your questions. The second two are blog posts, so if you have questions about the specifics in these articles you can post comments to them.

    The Basics of Global Warming
    How Warm is Too Warm?
    The Water Vapor Fallacy