Hmm. I was under the impression that burning garbage is different in that you are burning carbon that is already in play in the carbon cycle system - unlike burning coal, which without human intervention would never be introduced into the environment at such a rapid pace. I could be wrong! I was disappointed by the lack of an explanation, or even links to background on the science of this process. Just a puff/fluff piece IMHO.

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.

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".

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".

What's GWP? See here:

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

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.

> 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.

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...).

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

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

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.

Sitting in a hole in the ground is from whence it came. Trash collectors should be getting substantial carbon credits. Their credits should increase the deeper they manage to bury the stuff. Sending it into the atmosphere, especially near the Arctic circle, if atrociously bad.

"This solution is no better than coal-generated electricity"

I'm not sure that's true at all. The only way a waste-to-energy plant can import waste from cross-borders is by having R1 status, R1 being a measure of energy recovery from the municipal waste that is burned [1].

On top of this, the plants (generally) recycle the plastic / metal that isn't burned, sell the fuel ash (to stabilize roads, etc), cogenerate steam from additional energy production, and either sell back to the municipalities the natural gas generated by the organic waste digestors or use it to generate additional electricity.

[1] http://www.cewep.eu/information/publicationsandstudies/state...

But the ash doesn't stick around, does it? Do you have an order-of-magnitude estimate for the heating effects of the ash? I'm guessing it's trivial compared to carbon offset.

There seems to be some debate about whether particulate matter has a net-warming or net-cooling effect. It's difficult to estimate empirically, because there are so many uncontrolled variables.

http://en.wikipedia.org/wiki/Global_dimming

http://en.wikipedia.org/wiki/Global_cooling#Aerosols

Ash represents incomplete combustion. I'm pretty the engineers are motivated to ensure the ash is a minor waste product compared the gasses, but somebody should check me on that.

My understanding is that the garbage would be burnt anyway so better use it for heating.

Don't some of the modern systems have processes that mitigate the released ash?

I found their recycling systems to be even more impressive sounding than the garbage incineration