OK. Not clueless. But today we have yet more evidence that we really don't understand how this planet's carbon cycle works,thanks to the latest issue of the Soil Science Society of America Journal. In "Nitrous Oxide Emissions Respond Differently to No-Till in a Loam and a Heavy Clay Soil", a group of Canadian researchers makes it clear that our species is just plain ignorant when it comes to managing greenhouse gas emissions. It's looking like there is one fewer tool in the box of options at our disposal for mitigating global warming.
Until now, it was generally assumed by aggies the world over that no-till, also known as zero-tillage, farming, is a good thing, as it reduces erosion and increases organic matter. Essentially, the practice avoids disturbing the soil after harvest. Forgoing tilling also means less work and potentially lower costs for farmers. And, as evidenced by the Wikipedia entry, the conventional wisdom is it cuts down on carbon dioxide emissions and therefore poses a possible method of pulling back the reins on global warming.
NASA's James Hansen hasn't written about no-tilling specifically, as far as I know, but when he offers "improved forestry and agricultural practices" as one way of absorbing CO2 and bringing down concentrations below 350 ppm, this is one of the kind of things he's presumably talking about.
But along comes Philippe Rochette and his colleagues at Canada's Department of Agriculture and Agri-Food with their analysis of gas exchange between some clay-soil farmland at the atmosphere. For some reason, their experiment was carried out several years ago, from April 2001 to November 2003, but it isn't the timing that's important. Here's what they found:
Adoption of NT [no-till] practices has several benefits including reduced energy inputs and soil erosion. Soil C stocks are also often increased under NT compared with conventional tillage practices. Such C gains are a sink for atmospheric CO2, which contributes to decrease net GHG from farms. Our results indicate, however, that NT can result in incremental N2O emissions that can more than offset the soil CO2 sink during the first 5 yr after adoption of this soil conservation practice in a heavy clay soil.
So, yes, there is a net drawn-down of CO2 from the air, but a net release of nitrous oxide. And when you normalize for each gas' heat-trapping ability, the end result is an increase in planet-warming effects.
There are lots of limitations to this study, of course. For one thing, it involves heavy clay soils, the kind found in much of Quebec and elsewhere in eastern Canada. But that doesn't mean the same kind of nitrogen movement will be found in other soils. So it could be that no-till practices, if used everywhere on Earth they make sense, would still represent a net sink of greenhouse gases. Rochette et al. write that "the potential of NT for decreasing net GHG emissions may be limited in fine-textured soils that are prone to high water content and reduced aeration."
On the one hand, it's always good to know things like this. It prevents us from embracing what we thought was a good idea but turns out to be making things worse. On the other, it reminds us just how little we really know about carbon cycles, and how foolish are these geo-engineering schemes that some would have us pursue in hopes of preventing catastrophic climate change. We simply aren't equipped with the sophisticated understanding required to go about tinkering with planetary heat and carbon budgets.
Some would argue that we have to take the chance, so close are we to irrevocable tipping points, and so unlikely are we to voluntarily stop burning the fossil fuels that are the cause of the problem. But given the choice between doing what we know with a high degree of confidence will slow global warming ;;;; shut down the coal-fired plants and so forth ;;;; and running wild with some hairbrained scheme to reset the planet's thermostat, I'll choose the first option, even if the political challenge involved is enormous.
--
P. Rochette, D. A. Angers, M. H. Chantigny, N. Bertrand (2008). Nitrous Oxide Emissions Respond Differently to No-Till in a Loam and a Heavy Clay Soil Soil Science Society of America Journal, 72 (5), 1363-1369 DOI: 10.2136/sssaj2007.0371
- Log in to post comments
More like this
Quoting those crazy Canadians again. Goober
This post brings to mind what may be the most important mystery of the carbon cycle: as each glaciation comes to an end, retreating ice sheets appear to drive rising CO2 levels; the carbon cycle appears to act as an amplifier for warming due to ice-sheet retreat and due to Milankovitch cycles. Why does this happen? Will human-induced warming be similarly amplified by the carbon cycle? If so, how strong will the amplification be, and when will it start happening?
A few possible contenders:
(a) Melting permafrost. Permafrost is known to contain hundreds of gigatons of carbon, and can release it as CO2 and/or methane It's melting. It may be releasing globally significant amounts of CO2 and/or methane. Monitoring is not sufficient to determine whether this is yet globally significant. Recently, many large plumes of methane were found escaping from undersea permafrost north of Siberia, and near Svalbard. These plumes may be a recent phenomenon - or they may be a long standing phenomenon - or a combination of both. After having remained stable for about 10 years, global atmospheric methane content appears to be on the rise again - but it's not clear these plumes are to blame.
(b) Drying wetlands. Much of the world's wetlands are in areas that are presently getting drier due to AGW, and forecast to keep getting drier due to AGW. Wetlands contain huge amounts of carbon. They release CO2 when they dry. Again - monitoring is not sufficient to know of this CO2 release is globally significant.
(c) Drying forests. Like wetlands (and there is plenty of overlap, e.g. much of tropical rain forests) much of the world's forests are in areas that are presently getting drier due to AGW, and forecast to keep getting drier due to AGW. Forests contain huge amounts of carbon. They release CO2 when they dry. Again - monitoring is not sufficient to know of this CO2 release is globally significant.
(d) Methane clathrates. I think this topic is already covered enough elsewhere.
One might also infer from the fact of 'how little we really know about carbon cycles' that perhaps we should not be mandating highly risky and tremendously expensive interventions in the economy.
I am not saying that there is not a problem with carbon emissions, and I am not saying that we should ignore them. But look at the Fed and the Treasury - they analyze the data, claim there's a problem, raise $700 billion, and less than two weeks later, they're doing completely different things with that money than what they originally planned to do, and, as far as I can tell, every reputable economist is pretty much shrugging their shoulders saying "I guess they know something I don't, but I don't understand what their strategy is"
And the world's financial system is arguably far less complex than the world's ecosystem.
So perhaps, instead of blundering around sowing seeds of fear and demanding mindless obeisance to the pronouncements of the climate elite, we should demand that they spend some more time actually, you know, understanding all of these things before they start making 'do this or millions/billions will die' predictions.
Yes, you are:
Anthropogenic climate change has been studied for years, and almost all of the data from continuing studies indicates that the situation is getting worse. Insisting that 'understanding all of these things' before doing anything is exactly the same a arguing that we can never do anything, since we will never understand anything to your satisfaction. This is the same approach that creationsists like Dembski use to attack evolution - because we cannot demonstrate the exact sequeqnce and timing of every single mutation that separated man from monkeys, it did not happen.
Also, it is incredibly insulting to climatologists (I am not one) to compare their desire to ameloriate the situation with the recent financial bailout where Congress failed in their duty to investigate even a little bit before capitulating to Bush, Paulson, and the others who were directly responsible for the mess in the first place.
Why does soil hate America?
Shorter jb: the Fed and the Treasury changed their minds in less than two weeks therefore we should not trust climatologists. Is that a fair summary of your argument?
Regarding accumulation of organic matter in soil; it is negligible in many tropical soils because the higher temperatures promote the activity of decay organisms.
I always knew James was a Goober. Good to hear my suspicions confirmed about being clueless too.
This is the reality...not nice.
Australia's Stern review warns of runaway global warming
"Carbon emissions are rising so fast that the world has no chance of hitting climate targets, says Australian economist"
http://www.guardian.co.uk/environment/2008/oct/27/climate-change-austra…
The only way that we can limit the rise to 2C is if we have a deep global depression now and throw everything in to coming out of it with zero emission technology!
Even at 2C we might have gone past major thresholds so its still fingers crossed.
A nagging concern I have is that fossil fuels are effectively permanent CO2 draw down. I can't see how any sizable part of these reserves would have naturally been reintroduced back in to the atmosphere.
We have now effectively put back a huge amount of carbon that would not have found its way back over the inter-glacial cycles. This is completely bucking the natural progression.
This probably means that we are in for big time warming no matter what we do.
On top of the GW effect the small addition of heat energy from using these fossil fuels probably stacks the equilibrium even more, although it's only is a fraction of the equation.
Whats worse than rising sea-level and monster storms?�
may be were not addressing this enough.
�The Darkening Sea�
http://www.earthtimes.org/articles/show/new-documentary-on-the-oceans-a…
��the effects of climate change are not limited to global warming: they extend to the sea, where the chemistry of the water is being changed and creating a profound threat to the food chain, starting at the bottom.�