In the face of ever mounting evidence that CO2 is incapable of causing the level of global devastation prophesied by climate change catastrophists a new villain is being sought. The leading candidate is nitrous oxide (N2O), better known as laughing gas. A report in Science claims that N2O emissions are currently the single most important cause of ozone depletion and are expected to remain so throughout the 21st century. The IPCC rates N2O as 310 times as potent a greenhouse gas as CO2 on a 100 year time scale. Is this a greenhouse gas bait and switch, or are the global warming alarmists trying to up the ante?
Nitrous oxide is a colorless non-flammable gas with diverse uses. It is used as an oxidizing agent to boost power output from internal combustion engines and as a propellant for canned whipped cream. Historically, it was used as an anesthetic in surgery and dentistry. Inhaling the gas can cause euphoric effects, which led to it being named “laughing gas.” Public exhibitions and private “happy gas” parties were all the rage during the mid-19th century. Recreational use continues to this day, but for the environment N2O may be no laughing matter.
A. R. Ravishankara, John S. Daniel, Robert W. Portmann, all scientists at the US National Oceanic and Atmospheric Administration Earth System Research Laboratory, claim that limiting future N2O emissions would enhance the recovery of the ozone layer from its depleted state and would also reduce the anthropogenic global warming (see “Nitrous Oxide (N2O): The Dominant Ozone-Depleting Substance Emitted in the 21st Century”). They call reigning in the currently unregulated gas a “win-win for both ozone and climate.” This is because, while N2O on its own is a potent GHG, it also damages the ozone layer which protects Earth's surface from UV radiation and provides a cooling effect for the atmosphere.
Earth's atmosphere and ozone layer. Credit: NOAA.
I have previously commented
on the Global Warming Potential of various greenhouse gases but not addressed nitrous oxide specifically. N2O was one of the GHGs that the IPCC claimed to understand in their last full report (AR4). Also included in the general category of greenhouse gases was ozone (O3), though the confidence level was only rated as “medium” for its contribution. As can be seen from the chart below, ozone behaves differently in the lower atmosphere (troposphere) and upper atmosphere (stratosphere). It is the stratospheric ozone layer that N2O damages, reducing the cooling effect of that layer.
As you may recall, depletion of the stratospheric ozone layer by human-made chemicals, referred to as ozone-depleting substances (ODSs), was one of the major environmental issues of the 20th century. As a result of the Vienna Convention for the Protection of the Ozone Layer most of the world's nations signed the Montreal Protocol on Substances That Deplete the Ozone Layer (MP). The MP has been highly successful in reducing the emissions and concentrations of chlorine- and bromine-containing halocarbons limiting ozone depletion and helping recovery of the ozone layer. These substances can be tens of thousands of times more potent GHGs as CO2 and were the historically dominant ODSs. Since these man-made substances have been successfully regulated scientists have turned their attention to N2O as the next most potent threat to Earth's ozone layer.
Nitric oxide and nitrogen dioxide (NO and NO2), generically referred to as nitrogen oxides (NOx), are known to catalytically destroy stratospheric ozone. The primary source of stratospheric NOx are surface N2O emissions, hence the new interest in nitrous oxide emissions. Nitrous oxide shares many similarities with the now banned chlorofluorocarbons (CFCs). N2O, like CFCs, is stable when emitted at ground level, but breaks down when it reaches the stratosphere to form nitrogen oxides, which in turn trigger ozone-destroying reactions. Both substances have human emissions sources but, unlike CFCs, N2O also has natural sources.
Nitrous oxide is emitted from soil fertilization, livestock manure, sewage treatment, combustion and certain other industrial processes. In nature, bacteria in soil and the oceans break down nitrogen-containing compounds, releasing N2O. About one-third of global nitrous oxide emissions are attributed to human activities. Ravishankara et al. report that N2O is now ozone enemy number 1:
Even though N2O’s ODP is only 0.017, roughly one-sixtieth of CFC-11s, the large anthropogenic emissions of N2O more than make up for its small ODP, making anthropogenic N2O emissions the single most important of the anthropogenic ODS emissions today. For example, the global anthropogenic emission of N2O now (produced mainly as a byproduct of fertilization, fossil fuel combustion and industrial processes, biomass and biofuel burning, and a few other processes) is roughly 10 million metric tons per year compared with slightly more than a million metric tons from all CFCs at the peak of their emissions.
Here ODP stands for ozone depletion potential, which compares the amount of stratospheric ozone destroyed by the release of a unit mass of a chemical at Earth’s surface to the amount destroyed by the release of a unit mass of chlorofluorocarbon 11, CFC-11 (CFCl3). The researchers conclude that, if N2O emissions continue unabated, their impact could be 30% higher than the CFC peak in 1987. Ecologists and environmental activists count the rescue of the ozone layer as a major triumph, does this mean that the celebration was premature? Are we certain that the ozone layer is once again threatened by human emissions? Here is what the study says:
It should be noted that the largest uncertainty in ODP-weighted emission comparisons comes from the uncertainties in the emission estimates of N2O, rather than in the calculated ODP. The magnitudes of the sectoral emissions of N2O, mostly from agricultural practices and industrial sources, are highly uncertain, but the total human-caused emissions are constrained by observed increases in N2O concentrations and N2O’s lifetime.
As with carbon, all the intricacies of the nitrogen cycle are not understood by modern science. In particular the mechanisms that convert free nitrogen gas, N2, into biologically useful compounds. “Current global ocean nitrogen budgets do not balance, which suggests that existing models miss or underestimate some contributions to oceanic nitrogen fixation,” reports Robinson W. Fulweiler in a perspecive article (see “Fantastic Fixers
”) from the October 16, 2009, issue of Science. Moreover, recent studies have found higher rates of nitrogen fixation in coastal sediments and more abundant nitrogen-fixing organisms in the open ocean than previously suspected.
In that same issue of Science Anne E. Dekas et al. describe a community of archaea and bacteria in deep-sea sediments that can fix nitrogen. Their report, entitled “Deep-Sea Archaea Fix and Share Nitrogen in Methane-Consuming Microbial Consortia
,” reveals direct evidence of a previously unknown environment for nitrogen fixation that can deliver biologically usable nitrogen to deep-sea sediments. This exciting study provides a link between the carbon, nitrogen, and sulfur cycles.
Dekas et al. used the Alvin submarine to sample sediments from a seep off the coast of California. Credit : Victoria Orphan, California Institute of Technology
According to the study: “Using single-cell–resolution nanometer secondary ion mass spectrometry images of 15N incorporation, we showed that deep-sea anaerobic methane-oxidizing archaea fix N2, as well as structurally similar CN–, and share the products with sulfate-reducing bacterial symbionts. These archaeal/bacterial consortia are already recognized as the major sink of methane in benthic ecosystems, and we now identify them as a source of bioavailable nitrogen as well.”
Many mysteries still remain, such as why N2 fixation in anoxic marine sediments, which often contain ammonia compounds, should occur at all. These findings have important implications for Earth's environment and once again highlight how much mankind doesn't understand about nature. “The current discrepancy in the oceanic fixed N budget underscores the possibility of new sources of fixed N in nontraditional and potentially unexpected habitats,” the study concludes. “N2 fixation in ANME-2, combined with the diversity of nifH genes recovered from marine sediments here and previously, suggests that our inventory of marine diazotrophs is incomplete and that we are only beginning to understand the extent and importance of benthic marine N2 fixation.”
If there is an effort afoot, to shift the focus of climate change study from CO2 to nitrogen compounds, it may be ill advised—it appears that the nitrogen cycle is as poorly understood as the carbon cycle. One final warning comes from Ravishankara et al.: “N2O could be an unintended byproduct of enhanced crop growth for biofuel production or iron fertilization to mitigate CO2 emissions. Such an enhancement would lead to the unintended "indirect" consequence of ozone layer depletion and increased climate forcing by an alternative fuel used to curb global warming.” In other words, we had best be damned careful in our efforts to “cure” global warming.
Indeed, according to P. J. Crutzen et al., writing in Atmospheric Chemistry and Physics (see “N2O release from agro-biofuel production negates global warming reduction by replacing fossil fuels
”), much of the rush to biofuels could actually be worse for the environment than current fuels. Their 2007 study reported: “When the extra N2O emission from biofuel production is calculated in "CO2" 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.”
Global warming may be laughable but the scams are not.
This knowledge has not dampened the enthusiasm for ethanol and biodiesil in some quarters. Ignoring repeated reports
that biofuels are bad for the environment, governments around the world press ahead with expensive subsidies for their production. Biofuels
, clean coal
and cottage industry solar power
are just a few of the scams that have popped up to take advantage of global warming hysteria. Climate scientists are reassessing the accuracy of climate change claims but the true believers continue to preach imminent disaster. Global warming is the scam of the century and it won't be going away anytime soon—there's too much money to be made and political influence to peddle. And the biggest climate change scam of all is about to resurface in America, it's called Cap and Trade.
Be safe, enjoy the interglacial and stay skeptical.