[jlgreco]

It would really depend on what is being burnt. If it is primarily food waste, paper products, natural fibers, wood, etc.. then yeah; all of that carbon was already "in the system". If they are burning lots of garbage made from petrochemicals then that garbage is basically just another fossil fuel.

As I understand it, the real issue with "clean coal" is not the soot but rather the CO2. Depending on what this garbage actually is, the CO2 problem isn't really a problem in this case.

[stephengillie]

I found a case study about Oslo's waste management strategy: http://www.c40cities.org/c40cities/oslo/city_case_studies/wa...

The study emphasizes their focus on composting for food products and recycling everything else, so a minimum of waste needs to be incinerated or dumped. Also, Oslo closed their landfill in 2007, and it seems they burn the residual gasses (methane?) for electricity, if not burning all of their old trash. The report focuses on home recycling requirements, but does not mention commercial or industrial waste, which are by far larger generators of waste.

So, it seems likely that the incinerated waste is not "in-system".

[jlgreco]

Surely burning that methane is "in-system". Methane has a 20-year GWP of 72 and, unless my chemistry is far more rusty than I think it is, 1 mol of methane will burn with oxygen to form 1 mol of CO2. From a global warming standpoint, it would actually be wildly irresponsible to not burn that methane. In fact this seems to be the basis for the EPA's "Landfill Methane Outreach Program".

[niels_olson]

What's GWP? See here:

http://en.wikipedia.org/wiki/Global-warming_potential

[jlgreco]

Aye. This (http://en.wikipedia.org/wiki/Global-warming_potential#Values) chart is important to consider too. I gave the 20-year GWP value for CH4, but CH4 does not last as long in the atmosphere as CO2 so that value drops as time progresses. However even the 500-year GWP for CH4 is still above CO2.

[niels_olson]

> in the system

That doesn't make it better. We have too much carbon in the atmosphere. We should be growing corn for the sole purpose of pouring it into oil wells and coal shafts.

[jlgreco]

It is certainly better than adding more greenhouse gasses, which is what fossil fuels do. Burning, for example, wood obviously does not reduce greenhouse gasses (nor does anyone claim that), but from a greenhouse gas standpoint it is clearly way better than digging up even more CO2. There are certainly other very important factors to consider, but if the discussion is global warming than you can give me a tree farm over a coal mine any day.

Dumping corn down mineshafts seems like it would be pissing in the ocean. Maybe instead of pissing in the ocean we should be experimenting with dumping fertilizers and nutrients into the ocean to trigger algae blooms. If that works as the theories say it should, and is seen to have acceptable consequences, that is something that we could actually do at scale (and without further subsidization of corn...).

[ericd]

Which would largely turn back into CO2 once the bacteria do their thing.

[niels_olson]

Erm, I believe it would turn back into oil and coal, etc.

[ericd]

We're not entirely clear on how that works, and our best estimates are that it takes on the order of hundreds of thousands of years and requires quite a bit of pressure. The proposal above would basically be a deep landfill, and generally what will come from landfills in our lifetime is methane, CO2, dirty water, and a lot of garbage sitting around.