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Study: N2O Emissions from Biofuel Crop Production Negates Greenhouse Gas Benefits of Using Biofuels

Relative warming derived from N2O production for crops, crop residues, and forages used in the production of biofuel. Click to enlarge.

A new study led by Paul Crutzen, winner of a Nobel Prize in Chemistry in 1995 for work on the formation and decomposition of ozone in the atmosphere, re-examines the total emission of nitrous oxide (N2O) from crop production and concludes that growing and burning many biofuel crops may actually raise, rather than lower, net greenhouse gas emissions.

N2O is a by-product of fixed nitrogen application in agriculture and is a greenhouse gas with a global warming potential (GWP) 296 times larger than an equal mass of CO2.

Crutzen and his colleagues calculated that growing some of the most commonly used biofuel crops releases around twice the amount of N2O than previously thought, thereby wiping out any benefits from not using fossil fuels and potentially contributing to global warming.

When the extra N2O emission from biofuel production is calculated in “CO2-equivalent” global warming terms, and compared with the quasi-cooling effect of “saving” emissions of fossil fuel derived CO2, the outcome is that the production of commonly used biofuels, such as biodiesel from rapeseed and bioethanol from corn (maize), can contribute as much or more to global warming by N2O emissions than cooling by fossil fuel savings. Crops with less N demand, such as grasses and woody coppice species have more favourable climate impacts. This analysis only considers the conversion of biomass to biofuel. It does not take into account the use of fossil fuel on the farms and for fertilizer and pesticide production, but it also neglects the production of useful co-products. Both factors partially compensate each other. This needs to be analyzed in a full life cycle assessment.

—P. J. Crutzen et al.

The significance of it is that the supposed benefits of biofuels are even more disputable than had been thought hitherto. What we are saying is that [growing many biofuels] is probably of no benefit and in fact is actually making the climate issue worse.

—Keith Smith, a co-author on the paper and atmospheric scientist from the University of Edinburgh

The work is currently subject to open review in the journal Atmospheric Chemistry and Physics. Crutzen has declined to comment until that process is completed. The paper suggests that microbes convert much more of the nitrogen in fertilizer to nitrous oxide than previously thought—3 to 5 percent, compared to the widely accepted figure of 2 percent used by the International Panel on Climate Change (IPCC) to calculate the impact of fertilizers on climate change.

For rapeseed biodiesel, which accounts for about 80 percent of the biofuel production in Europe, the relative warming due to nitrous oxide emissions is estimated at 1 to 1.7 times larger than the relative cooling effect due to saved fossil CO2 emissions. For corn bioethanol, dominant in the US, the figure is 0.9 to 1.5. Only sugarcane bioethanol—with a relative warming of 0.5 to 0.9—looks like a better alternative to conventional fuels.

As release of N2O affects climate and stratospheric ozone chemistry by the production of biofuels, much more research on the sources of N2O and the nitrogen cycle is urgently needed...Here we concentrated on the climate effects due only to required N fertilization in biomass production and we have shown that, depending on N content, the use of several agricultural crops for energy production can readily lead to N2O emissions large enough to cause climate warming instead of cooling by “saved fossil CO2”. What we have discussed is one important step in a life cycle analysis, i.e. the emissions of N2O, which must be considered in addition to the fossil fuel input and co-production of useful chemicals in biofuel production.

We have also shown that the replacement of fossil fuels by biofuels may not bring the intended climate cooling due to the accompanying emissions of N2O. There are also other factors to consider in connection with the introduction of biofuels.  We have not yet considered the extent to which the high percentage of N-fertilizer which is not taken up by the plants, and the organic nitrogen in the harvested plant material, may stimulate CO2 uptake from the atmosphere; estimates for this effect are very uncertain. We conclude, however, that the relatively large emission of N2O exacerbates the already huge challenge of getting global warming under control.

—P. J. Crutzen et al.



NO2 is not N2O

in the atmosphere, NO2 reacts : NO2 + H2O --> H2NO3 which is highly soluble in water, and rains down (to form acid rain) and become nitrates (which is a fertiliser).
N2O does not react in the atmosphere, is higly unsoluble in water, and is only broken down by cosmic radiation in the higher atmosphere (which takes many decades).


==but I am also aware that biofuels have an impact today unlike other alternatives==

Assuming by "impact" you must mean, "making things worse".

==are a decade away from matching ethanol's current impact on oil consumption==
Corn Ethanol makes virtually no impact on reducing fossil carbon consumption.

It also makes virtually no impact as compared to our growth in transport fuel demand. Which is expected to double by 2025.

And ethanol likely increase our fossil carbon consumption.

And according to the GAO, corn ethanol legislation will actually increase our petroleum consumption by 9 billion gallons.


Actually, the Phoenix isn't that costly.

I'm also looking forward to their $35,000 SUV model.

Not to mention, I'm also not including any tax credits, which so far seem like they might be in the $4000-$10000 range.


Jim G wrote: All the replies regarding arctic trees make sense. I wasn't expressing my question clearly, which was more this: in a few decades, if the icy simply isn't there anymore for ten months of the year, and so can't be called 'permafrost' anymore, would we want tree cover or grass cover to replace it?

In that event, trees. Grasses live ~1 yr, trees live a few decades; trees are woody and much more massive than grasses; so trees sequester far more carbon.

Henrik wrote: Grey what is your source for the 100-200 years residence of CO2 in the atmosphere? For all I know it is incorrect. David Archer at the University of Chicago says “The mean lifetime of
anthropogenic CO2 is dominated by the long tail, resulting in a range of 30–35 kyr.”.

Not to speak for GreyFlcn, but there are several timescales for CO2. CO2 is controlled by terrestrial biota on the timescale on order 10^1 yrs; ocean uptake on the timescale on order 10^2 yrs; mineral weathering on the timescale on order 10^4 yrs; orbital variations on order 10^5 yrs (operates through temperature); and tectonics, on the timescale on order 10^8 yrs. There is also a marine biota term that responds so quickly (about 10 days) that it establishes equilibrium for a given climate condition.

The appropriate timescale to use depends on the question you ask. If you're asking about how long it will take to equilibrate, then the answer is on order 10^4 yrs if you're looking at current tectonic conditions (continents and mountain ranges where they are), 10^8 yrs if you're looking at Earth history. If you're interested in climate effects on a 100 yr timeframe, you would be more interested in the terrestrial and oceanic terms -- this is why the IPCC reports use a 5-200 yr timescale for CO2.


Thank you dt

I am interested in knowing the long term equilibriums or steady states of CO2 emissions versus N2O or CH4 emissions simply to make a conclusion about which is the most potent greenhouse gas in the long run. My experience with such modeling arrives from much simpler economic models but the mechanics should be much the same as it is in climate modeling.

Dt, you are basically braking down the distribution of the >mean lifetime< of anthropogenic CO2 of 35000 years that David Archer is talking about. My conclusion on this issue is unchanged, namely, that the long term impact of N2O or CH4 as greenhouse gasses is very, very limited when compared to CO2. With N2O if we emit a constant level each year at a higher level than the level nature used to emit before the agricultural revolution we will increase the average temperature of the planet gradually until we reach a new higher equilibrium level after just 120 years or so. Do the same experiment with CO2 and that equilibrium level of higher temperatures on the planet will not even have settle after 35000 years. The temperature will still be increasing. As you mention the tectonics CO2 works on the timescale on the order of 10^8 yrs so full CO2 warming equilibrium is first reached after 100 million years.

I worried about the Global Warming effect of CO2 before I learned this. Now I am convinced that the survival of mankind is at stake. If we don’t stop the CO2 emissions we will eventually make this planet inhabitable. The climate will become so warm that it will be impossible to grow any biomass. It may take several generations but it will happen if nothing is done. And the process of warming may be unstoppable in just a few decades. Al Gore said yesterday 24, September 2007 this planet needs a Marshall plan for GW and we need it now.

Jim G.

Yes, and one thing we don't need is professional obfuscation to baffle and redirect the public. I'm amazed to see a reference to Bjorn Lomborg in here. If only the volume of such people's megaphones varied directly with the truth of their words rather than the quantity of cash that pays to have them uttered. There are thousands of sincere, honest people who know what they're talking about who couldn't get half the media attention he gets for his dissemblings.

But observing this apparently makes you an "enviro-fundamentalist". You know, buddies with Osama and the Taleban.


Henrik -- you are asking questions with no easy answers. The thing is, the "mean lifetime" is difficult and rather pointless to assess: the timescale of the question is key. If you're talking geological ages, CH4 and N2O are minor players and CO2 is the big daddy. But there are exceptions: one of the leading candidates (or at least major contributors) for the end-Permian event is the "Giant Cow hypothesis", a massive release of methane. Estimates of up to 90% loss of all life are given for that, and it took millions of years to recover. Yet in the end, recover it did. On shorter timescales, N2O and CH4 may be quite important.

I'm extremely skeptical that we can extinguish life on this planet -- Life is incredibly resilient. Many large mammals are threatened, many of them found primarily in reservations; large fish populations are down 90%; some creatures have been driven to extinction. But microbes will do fine, as will insects, and in the oceans we're already seeing more and more invasive algae and jellyfish. What we can do is make ourselves and many of our fellow plants and animals miserable, reduce our ability to feed ourselves and acquire fresh water, quite possibly end our way of life as we know it (quite likely if we don't get on the ball right now). There is a limit to the amount of fossil fuel we can burn and therefore the amount of carbon we can put into the atmosphere, though that limit will likely lead to temperatures much higher than we want to maintain. IMO it is too late to avoid significant and expensive change at this point, but not too late to avoid really drastic change.



I like Robert Rapier's blog, but his article about ethanol not displacing petroleum used incorrect data. I got him to correct the data, but he held fast to the erroneous conclusion. I'll revisit with him as we get updated data. Should be fun.

I agree ethanol today does not reduce greenhouse gas emissions. The same is true of PHEVs/EVs fed by coal plants (Tesla claims otherwise but their recent 310 Wh/mile data argues against them). My main interest is reducing oil imports, which I consider a more pressing issue for the USA. Ethanol has a small impact today, PHEVs have none and won't for many years.

The GAO study's "9 billion gallons" comes from the FFV CAFE loophole, which I agree is an abomination.

Phoenix's $45k price is a scam. It might as well be 45 cents. The battery pack alone costs them about $80k. Their angle is to sell the SUTs at a huge loss in California but capture CA ZEV Type III credits. Since the only other way to get a Type III credit is to build a million dollar-ish fuel cell vehicle, Phoenix expects to sell the credits to major automakers for $200k+ each. Total revenue to Phoenix is thus $245k per truck. A nice trick if it works, but don't pretend for a minute that $45k represents any kind of real-world price.


Dt thank you once more.

It is a relief that you think that extinction of all life is very unlikely although the more likely alternative scenario of CO2 business as usual by human until mass extinction of life becomes a reality with the few survivors being microbes and insects is not that comforting either. Technology should also be able to save humans from dying completely out on a very warm planet. I mean we could move indoor in air-conditioned buildings and instead of normal open land farming it should be possible to do it industrially using a high tech bio industry.

I have been reading up a bit on the end-Permian event and the theory about the massive release of methane. I had heard about this phenomenon in lakes but that it can happen in the ocean that I did not know. This is really fascinating but also scary to read about and I will spend more time on that for sure.

This also gives an idea for what might happen in the worst case global warming event. In that case we will burn of the remaining 50% reservoir of oil and natural gas during the next 50 years and the remaining 90% reservoir of coal during the next 200 years. This will trigger a much warmer planet possibly 5 degrees Celsius hotter at equator and 20 degrees Celsius warmer at the poles and this will subsequently heat the oceans all the way down to the ocean floor. That will take some time possible several hundreds of years or a millennium. Now with a heated Ocean floor the gigantic reservoir of methane is being released and that creates the truly massive extinction of life on the planet. If what I understand is correct there is enough methane on the ocean floor so that if it is released in the atmosphere and burn it will importantly decrease the percentage of oxygen in our atmosphere (now at 20%, nitrogen counting for most of the remaining 80%) and multiply the level of CO2 several times creating a massively increased global warming effect. That effect will be further multiplied by increased water vapor in the atmosphere but thank god it will be decreased heavily by the albedo effect being clouds in the sky reflecting solar radiation. In this world we would most likely never be able to see a blue sky or a starlit heaven because 100% of the atmosphere at any given time will be covered in dense clouds (today it is about 50%). These clouds would be the only important thing left that cooled the earth and protected the remaining life from dying out. However, what a life. We would have to live in a dark, hot and very humid world full of insects and microbes but else with very little animal and plant life. If that was not enough because of the hot atmosphere the hurricanes in that world would be extremely violent compared to present time hurricanes. Earth would become a living hell compared to its incredible beauty right now. The only relief would be that if humans did survive this warming crisis we would do so only because of technology far more advanced than what we have today and most of us would probably do just fine living inside a high-tech building.

Well this is just a scenario and hopefully I have overlooked something that would make it impossible. I am not an expert in this area so I have most likely overlooked many important issues. Nevertheless, I think we should wake up and stop GW as much as we possibly can. If not for ourselves then we should do it for the sake of the future generations.


Well, crisis for some is opportunity for others. Those with generational turnovers in the weeks to ~year timeframe will roll with punches and will likely adapt to take advantage of new niches opening up. Those with turnover times on the order of decades may well find themselves under duress. I saw a Pentagon prediction a few years ago: War, famine, mass migration. I'm afraid they'll be right if we don't get moving. In the US we'll be shielded from the first two for some time (unless you count Iraq), but if Americans think we have immigration issues now ... It's not like the writing isn't on the wall.

Anyway, a few points. I would be concerned, very concerned, about permafrost methane and shallow-water (continental shelf) clathrates. I would be less worried about deep ocean floor methane -- it is less the temperature than the pressure that keeps them stable there. But there is more than enough to worry about if the permafrost and shelf methane outgasses.

I wouldn't look too heavily to technology. We have the necessary technology now, just not the will. The best technology of the future won't help us if we don't have the will.

Finally, you might read Michael Benton's When Life Nearly Died, which attempts to determine the cause of the end-Permian extinction. Also Peter Ward's Out of Thin Air for a somewhat speculative but interesting discussion of how low oxygen levels in a post-Permian world may have driven dinosaur evolution and why mammals took so long to become established. Neither will give you definitive answers -- these are active areas of investigation, and that's just the way it is.

but do keep in mind the Pentagon wears war-colored glasses. War and insecurity spells job security for them.


Just a simple question to all you clever people out there. I came accross some information about producing H2 from steam electrolysis, one option would be to use steam manufactured from a fluidised bed system, using woody crops as a feedstock. So we are not only driving turbines but producing hydrogen.
Now the question is, if we use that H2 to produce ammonia, then we could transport it with relative ease to the filling station where we could 'crack' it to produce hydrogen and nitrogen. If we use the hydrogen to power motor vehicles and vent the nitrogen to the atmosphere would this excess nitrogen have any effects on our atmosphere?



Now I have found some numbers on the GW potential measured in billions of tons CO2 equivalents. I have done some cross checking of the numbers and I think they are correct even though my primary source is Wikipedia which is often manipulated:

Total atmospheric CO2 current 2006 level: 800 billion tons.

Permafrost methane reservoir : 400 billion tons

All fossil fuel, coal oil gas: 5000 billion tons

Oceanic methane clathrate reservoir: 500-2500 billion tons

Natural gas (part of all fossils): 230 billion tons

Annual human CO2 emission 2006: 30 billion tons

If these numbers are correct I am not worried by the planets permafrost methane because it only equals about 13 years of human CO2 emissions if all that methane was released. Furthermore, it is only some of the current permafrost area that warms and might release its methane and it will not happen fast but take decades if not hundreds of years even when induced by massive global warming. There is a current measure of 3.8 million tons of methane released annually from the Siberian permafrost ( and this is actually very little compare to the 600 million tons of methane released from all sources combined see Also we follow methane concentrations in the atmosphere and it seems to have stopped its growth trend in the last decade

What I do worry about is the annual 30 billion tons of human CO2 emissions and I worry about a further release of some of the ocean methane of 500-2500 billion CO2 equivalents. Much of that could be released because of manmade GW in the first please that would subsequently warm the oceans and cause the methane to outgas but this warming will take a long time likely a millennium.
In general the situation is really grave but it should be possible to slow things down if we plant a lot of trees. There is an enormous reservoir of carbon stored in trees that grow on the planet. The source at Wikipedia say 1800 billion tons I do not know how to translate that in into CO2 tons equivalent but they can’t be far apart.

If we completely stop emitting CO2 within the next 40 years and start planting large trees big time at the melted permafrost areas and also start planting trees where we have agriculture right now and start producing food not by open land farming as we do now but in a high tech biomass industries then I think it should be possible to prevent mass extinction of life on our planet during the current millennium but otherwise not.


I agree ethanol today does not reduce greenhouse gas emissions. The same is true of PHEVs/EVs fed by coal plants.
Thats not entirely true.

Driving an EV or PHEV on Coal is like driving a hybrid in emissions.

Certainly not perfect, but far from "No benefit".


Driving an EV or PHEV on Coal is like driving a hybrid in emissions.

With coal around 2.1 lb CO2/kWh, Tesla's 310 Wh/mile tranlatest to 0.65 lb CO2/mile. A two-seater hybrid such as the Honda Insight averages around 50 mpg, or about 0.38 lb CO2/mile. A two-seater non-hybrid at 30 mpg would be about 0.65 lb/mile, matching the coal-fueled Tesla.

I found a really good source on the Global Warming potential of oceanic methane. Bruce Buffett and David Archer. University of Chicago. They should be some of the most regarded and most knowledgeable scientist in the field. The paper is good reading see

It does not look good at all in fact it is catastrophic already. I quote their article “Preferred values for these parameters are taken from previous studies of both passive and active margins, yielding a global estimate of 3*10^18 g of carbon (3000 Gton C) in clathrate and 2*10^18 g (2000 Gton C) in methane bubbles. The predicted methane inventory decreases by 85% in response to 3 degree C of warming.”

This is 5000 billion tons of pure carbon which translates into I believe about 10000 billion tons of CO2. Or 12.5 times the current level of CO2 in our atmosphere. If it only takes 3 degree C increase in the global temperature to release most of it the current global warming of now 0.7 degree Celsius only need to increase some 2.3 degree more to make that happen. The UN climate panel IPCC project is already predicting an increase of temperature by 1.1 to 6.4 °C (2.0 to 11.5 °F) between 1990 and 2100.

This is bad. In a few decades the climate will be warm enough to release the ocean methane and then it is a matter of a few hundred years more and then the planet will be about 10 degrees C warmer at equator and some 30-40 degrees hotter at the poles. They will melt with about 70 meter increase in sea level. And 99% of all life on the planet will die out because they cannot adapt. Will humans die out? It is not going to be easy to survive for sure and I do not think present day technology will help many people to survive. I think we will survive with much better technology and those who can’t do that will die. But why make the whole planet ugly with very few species left etc?

More info here.

We certainly live in a world of almost utter ignorance and lack of foresight. I hope these are the reasons and not just the cynical “hey we live great now and who cares about future generations we will be dead anyway when they start to suffer”.

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