A new paper by my colleague Chris Kucharik and I looks at the new US Energy Policy, will calls for growing more corn to produce ethanol, will affect the "Dead Zone" in the Gulf of Mexico. For a quick summary, see Reuters, the CBC or AFP (or my 15 Minuten ruhm on German ARD). Wired and Scientific American go into more detail.
The Mississippi dumps a massive amount of nitrogen, largely in the form of the soluble ion nitrate, into the Gulf each spring. It promotes the growth of a lot of algae, which eventually sinks to the bottom and decomposes. This consumes much of the oxygen in the bottom waters, making life tough for bottom-dwelling fish and creatures like shrimp. The Dead Zone has reached over 20,000 km2 in recent years.
The primary source of all that nitrogen is fertilizer applied to corn grown in the Midwest and Central US. Reducing the Dead Zone to less than 5000 km2 in size, as is suggested in US policy, will require up to a 55% decrease in nitrogen levels in the Mississippi.
The new US Energy Policy calls for 36 billion gallons of renewable fuels by the year 2022. Of that, 15 billion can be produced from corn starch. Our study found meeting those would cause a 10-34% increase in nitrogen loading to the Gulf of Mexico.
Meeting the hypoxia reduction goal was already a difficult challenge. If the US pursues this biofuels strategy, it will be impossible to shrink the Dead Zone without radically changing the US food production system. The one option would be to dramatically reduce the non-ethanol uses of corn. Since the majority of corn grain is used as animal feed, a trade-off between using corn to fuel animals and using corn to fuel cars could emerge.
Monday, March 10, 2008
Corn ethanol production will worsen the Dead Zone
Monday, June 25, 2007
Where does all that carbon go? Part II
Last week, Tamino at Open Mind, Eli at Rabbet Run and I began an experiment in mob-blogging’ about the carbon cycle. Following on our initial posts, profilic Eli has posted a couple interesting CO2 concentrations maps that highlight forest fires and fossil fuel emissions.
For a refresher on where all the carbon goes, the graph at right shows the IPCC's breakdown of the resting place, for now, of fossil fuel emissions over the past 25 years. The atmospheric build-up is measured (see Tamino's post) and the ocean uptake in well-constrained by measurement: that allows us to back-out the land uptake.
The drawback to this logic is that the land is both a prominent anthropogenic carbon dioxide source (e.g., deforestation, biomass burning) and a prominent carbon dioxide sink (e.g., net regrowth of vegetation). The positive uptake by land means that the sink is greater than the source. That, however, could change in the future, which would mean a larger fraction of carbon emissions would remain in the atmosphere. To answer that, it helps to study where the net carbon uptake occurring on land, and why?
One culprit is carbon’s chemical sibling nitrogen, that’s #7 on your periodic table if you’re scoring at home. Like many siblings, carbon and nitrogen are quite co-dependent, and, one might argue, a bit resentful about the whole thing. Carbon fixation - photosynthesis, plant growth – is limited by the availability of nitrogen. Though only up to a point. If there’s too much nitrogen, things get saturated, and the carbon-based plants pout and refuse to grow more.
You might find it strange that nitrogen is limited, given that N2 or di-nitrogen gas makes up the majority of the atmosphere. However, N2 is unreactive. It only becomes available to plants when converted to reactive form by microbes. In the process of making fertilizer and burning fossil fuels, we not only have increased the rate at which this conversion happens, leaving more nitrogen in our soils and waterways, we've emitted nitrogen in other reactive, gaseous forms, like nitrogen oxides or NOx. (eli, thanks for the suggestion - ed)
The IPCC map to the right shows nitrogen oxide (NOx) concentrations in the lower atmosphere. Notice the high levels above and downstream of North American, Europe and China. Deposition of this nitrogen could be increasing carbon fixation in forests.
A recent paper in Nature found just that: nitrogen fertilization, not forest regrowth after logging, may explain the majority of the net carbon sink in northern forests. The authors used chronosequences – yes, that’s a real word, not some star trek science word referring to data taken from a forest with trees of varying age that can be used to represent different stages of tree growth – to estimate mean carbon uptake at sites across the northern hemisphere.
By integrating uptake over entire rotations (from planting to forest replacement), the authors were able to get a more complete representation of carbon uptake by forests. Using that data, they found a strong relationship between nitrogen deposition and carbon sequestration, implying nitrogen fertilization may be driving the land carbon sink.
Nitrogen oxide emissions and nitrogen deposition are expected to increase in the future without tougher air pollution policies here and especially in Asia (see this paper). That could increase the carbon sequestration in northern forests, presuming those forests do not become N-saturated. Of course, hopefully the world will reduce NOx emissions and improve air quality. Unfortunately, that could also reduce carbon uptake and thus allow a larger fraction of carbon emissions to stay in the atmosphere.
Tuesday, October 03, 2006
Warming vs. heating
In his recent book "The Revenge of Gaia", the scientist James Lovelock of Gaia hypothesis fame uses the term global heating rather than the more common global warming. In an interview with the NY Times, Lovelock argued:
"Warming is something that’s kind of cozy and comfortable. You think of a nice duvet on a cold winter’s day. Heating is something you want to get away from."
The use of the word heating has caused debate among the sort of people who like to debate these things. Here are a few thoughts on the issue.
Is heating a more ominous word? I suppose it sounds more severe, more like something that you actively force, or is imposed upon you, than warming. Linguists can argue over that. Either way, Lovelock is advocating the use of the word because of the values he believes it communicates, namely that global warming / global heating / climate change is scary and dangerous. That may very well be true. But should such a conclusion be enshrined in the language used by scientists?
Yes, scientists are lousy marketers. You don't need to remind me of that. I work in a field called biogeochemistry. The only people that would voluntarily assume such a horrific label are scientists. Oh, scientifically, it makes senses. Geochemistry is the chemistry of the earth, so biogeochemistry is simply saying if you want to understand the chemistry of the earth, you have to take the "bio" - life - into account. But it sure ain't pretty.
The thing is, maybe we should be lousy marketers. Our objective is not supposed to be selling our results. Thanks to press releases, news articles, blogs and the like, the marketing of your science is often exactly what happens. It is with exactly that trend in mind that we need to be sensitive about using value-less terms to label our disciplines and our results.
I don't know whether people will respond differently to global heating or global warming or climate change. But I know we should not choose the language based on how people will respond, but which is most accurate (within reason, otherwise scientists will drone on for hours with caveats and confidence intervals).
If the media or activists want to take what by all rights should be called global climate change and call it global warming or heating, they can do so. Scientists? We should stick with the dull explanatory labels, whether it is climate change, or biogeochemistry.
