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Special Edition: Understanding ’s Potential to Amplify or Reduce

CLIMATE INSTITUTE Summer 2015 Volume 27, No. 1 Climate Alert A MESSAGE FROM THE CHIEF SCIENTIST Methane—the Other -Containing

Commentary by we first need to find an alternative nations would by now be well along Michael MacCracken means for securing the services that in cutting their emissions. Unfortu- fossil energy has been providing and nately, that has not been the case. In With good reason, more, given the continuing growth in the search for emissions pathways significant attention the global population. that could contribute to a near-term is being devoted to The global average temperature is slowing of the overall greenhouse sharply cutting emis- now up about 0.9°C over its prein- warming influence, we now have to sions of carbon diox- dustrial average and projected to rise go back and separate out the distinct ide (CO2). In general, emissions result further with the onset of the strong roles and lifetimes of each individual from combustion of , oil, and nat- El Niño that appears to be emerging. greenhouse gas and type of warming ural gas (together, fossil fuels) to pro- Furthermore, the rate of sea level or cooling . Continuing to use vide energy and, somewhat less im- rise is accelerating due both to addi- the hundred-year Global Warming portantly, from clearing of land for tional melting of the Greenland and Potential (GWP-100) would be ob- , products, and com- Antarctic ice sheets and greater up- scuring potentially effective policy munities. Using fossil fuels in particu- take. Coupled with the likelihood and options. lar transfers carbon that has been intensity of extreme weather increas- Recognition of this emerged almost tied up underground for tens of mil- ing, the rate the world’s nations are a decade ago in leading elements of lions of years to the coupled atmos- proposing to cut emissions is so mod- the scientific community at the NASA phere-upper -living biosphere est that it will not lead to a slowing of Goddard Institute for Space Studies system, which leads to an uptick in the rate of warming until well into and a bit later in our studies here at the atmospheric concentration. As a the second half of this century. By the Climate Institute (see http:// significant fraction of this will persist that time, the increase in global aver- www.climate.org/topics/climate- for millennia, and somewhat less for age temperature is projected to be change/maccracken-proposal-north- much longer, its implications are con- over 2°C and still rising. This means south-framework.html). The benefits cerning. that we will be headed to well above of a plausible set of actions were fur- Just this March, the CO2 concentra- the level of temperature increase ther studied in detail in a 2011 inter- tion at the Mauna Loa Observatory in that international leaders have national assessment sponsored by Hawai’i reached 400 ppm, up over agreed will cause, based on solid sci- the United Nations Environment Pro- 40% above its preindustrial baseline. entific results, quite disruptive im- gramme and World Meteorological Stabilizing the atmospheric concen- pacts on the environment and socie- Organization (published as Shindell, tration, much less bringing it back ty. et al., Science, volume 335, pages down, will require essentially cutting So what, if anything, can be done? 183-189, 2012). These studies all emissions to zero. The longer this To simplify the analyses for the nego- made it very clear that achievable takes, the higher the elevated CO2 tiation process, the warming effects reductions in emissions of methane, concentration will be, the longer it of the emissions of non-CO2 species and the precursors of will persist, and the greater the cli- have been combined together to cre- tropospheric ozone, all species that mate change and associated impacts ate a CO2-equivalent (CO2e) concen- have a relatively short atmospheric will be. On first sight, the intensifying tration based on the relative lifetime, could reduce the projected impacts would seem to be large strengths of their warming influ- warming by ~0.5°C, which is about enough to merit strong near-term ences, integrated over a 100-year half of the projected warming from steps to cut emissions. However, the period. This approach to approxi- the present out to 2050. This would fact that fossil fuels provide roughly mating how climate models treat the be a very important contribution to 80% of the energy providing food, full chemistry and warming influ- slowing the pace of global warming energy, and other services for the 7 ences of each individual gas was while at the same time providing a billion people on the planet means adopted a quarter of a century ago, number of benefits for human that the use of fossil fuels cannot when there were expectations that health, energy efficiency, and cleaner simply be ended. In order to do that, Page 2 Climate Institute | www.climate.org Climate Alert Volume 27, No. 1

air. Recognizing the importance of activities. Some include tightening up author Brooke Labonte, a Climate In- such efforts, Secretary of State Hillary emissions from oil and gas operations stitute Arctic Intern, is a recent gradu- Clinton with UNEP and representa- (as EPA is working on with new rules), ate of Ryerson University in Toronto, capturing emissions from waste dis- tives of five other nations launched Ontario, where she studied Geograph- the Climate and Clean Air Coalition posal and sewage sites, and reducing ic Analysis and Environment and Ur- (http://www.ccacoalition.org) emissions from the agricultural sector in 2012; it is now a growing interna- (e.g., from feed lots, chicken and pig ban . Their article high- tional effort to pursue reductions in operations, etc.). Even taking these lights the importance of the methane the emissions of these species. actions, the cycle in present and future climate For the past several years, the Cli- concentration seems likely to remain and the many uncertainties in our un- mate Institute has been encouraging roughly 1000 ppb above its preindus- derstanding of this cycle, especially efforts that will cut emissions of trial level of about 750 ppb, and the role of methanotrophs, and rec- these short-lived species. The most could become even higher if thawing ommends research to fill these gaps in far-reaching has been our contribu- of permafrost and clathrates leads to tion to the development of a new an increase in natural emissions. With our understanding. methodology for life cycle analysis the per mass effectiveness of me- (see thane as a global warming agent be- http://www.leonardoacademy.org/ ing as much as a factor of 100 times programs/standards/life-cycle.html). that for CO2 over a 20-year period, This methodology would accurately exploring possible options for pulling account for the effectiveness of the methane concentration down is cutting emissions of methane, black worthy of exploration. As a basis for carbon, and other species contrib- such analysis, it is vital to understand uting to climate change in limiting the natural sources and sinks of me- global warming, as well as more fully thane and the processes and factors treat related environmental and that influence them. health-related influences. We also This is what Lyle Zimmerman and published a special edition of Climate Brooke Labonte cover in the accom- Alert (http://www.climate.org/ panying article in this issue. A biolo- publications/Climate%20Alerts/ gist with undergraduate and masters Autumn2009.html) on black carbon, degrees from Stanford and a Ph. D and coordinated with Rotec on their efforts to install black carbon controls from MIT, Dr. Zimmerman estab- on jeepneys in Manila and trucks in lished and led his own research group Xian. We furthermore participated in at the UK MRC National Institute for the development by the international Medical Research in London. An Arc- Gold Standard Foundation in the es- tic Fellow with the Climate Institute, tablishment of a methodology for he has led the Climate Institute’s accrediting emissions reductions study of the methane cycle and espe- from clean stove replacement pro- grams in India and other nations. cially the role of methanotrophs With this issue of Climate Alert we (methane consuming bacteria and focus our attention on methane. archaea) in limiting damage from There are a number of very important both human-generated and naturally and effective actions that can be tak- occurring . His co- en to limit emissions from human

Page 3 Climate Institute | [email protected] Climate Alert CLIMATE CHANGE AND THE MICROBIAL METHANE BANQUET By Lyle Zimmerman & Brooke Labonte

ly important microorganisms. 2010 saw an eye-opening demon- Methane is terrifying not only due stration of the microbial response to to increasing industrial and agricul- methane in the . The tural emissions, which have nearly largest oil spill in history occurred tripled atmospheric methane con- about 1500 meters below the surface centration since 1750, but also be- as the Deepwater Horizon drilling rig cause of the potential for enormous blew out. In addition to oil, about a  Methane is a powerful green- releases from natural carbon reser- half million tons of , most- house gas, second only to CO2 in voirs beneath Arctic permafrost ly methane, was released on the sea- importance, with increasing pro- where warming is occurring most floor. If that methane had all bubbled duction from human activities as quickly. The prospect of retreating up to the , it would have well as imminent releases from ice belching a globe-altering dose of added about 1% to the annual global thaw of vast Arctic deposits this potent greenhouse agent has production in a single dose.  Methane’s brief atmospheric life- been highlighted by the sudden ap- Fortunately, companies time makes it especially im- pearance of deep craters on the aren’t alone in noticing that methane portant for addressing warming Yamal peninsula in Siberia, probably can be an energy source, and evolu- in the critical next few decades. from subterranean methane build- tion has had a head start of a few  Specialized microorganisms dom- up, and the observation of fields of billion years. Recent research has inate the global methane cycle. methane bubbles off the Siberian shown that methane-eating microbes  Key classes of microbes that con- coast and in arctic lakes. (methanotrophs) are virtually ubiqui- sume vast quantities of methane Methane’s physical properties and tous both on land and in the sea. remain unidentified and virtually atmospheric variations throughout They are even capable of removing unstudied. Earth’s climatic history are fairly well methane from the atmosphere at documented. However, relatively very low concentrations- literally Overview little is known about the microbial eating it out of the air- as well as con- organisms and processes that are suming enormous amounts seeping A sudden increase in atmospheric responsible for ~85% of global me- from marine sediments and even methane presents one of climate thane production and ~60% of its abrupt well blowouts like the Deep- change’s more frightening possible consumption. water Horizon spill. tipping points. As the principal com- These specialized methane-making Under pressure at depth, methane ponent of natural gas, methane is and -consuming single-celled life rising from the Deepwater Horizon increasingly replacing coal and petro- forms are found nearly everywhere wellhead dissolved in , with leum as an energy source, but its par- in Earth’s waters and sediments/ very little immediately reaching the ticipation in the global . Better understanding of their atmosphere (Figure 1A). Instead, the reaches far beyond its role as a fossil complex ecologies and response to dissolved gas appears to have trig- fuel. Second in importance only to climate change and other anthropo- gered dense local blooms of special- the much more abundant CO2 as a genic pressures is badly needed. ized methane-eating bacteria. These climate-warming greenhouse gas, Whether or not these microbial ecol- bacterial plumes spent several methane (CH4) currently contributes ogies can be harnessed for climate months gorging on this methane ~14%1 of man-made atmospheric mitigation, learning more about buffet and then mysteriously disap- ‘’ (greenhouse warm- them is essential for avoiding poor peared, leaving behind a trail of nu- ing). Ubiquitous microbes are ulti- decisions that might inadvertently trient and depletion in the mately responsible for both creating exacerbate warming. local waters (Figure 1B) signifying and consuming most of this powerful high rates of bacterial metabolism in greenhouse gas, but science is only The Deepwater Horizon Bacterial the presence of a concentrated me- just beginning to identify and under- Buffet thane food source (Figure 1C) stand the basic of these vital- {Kessler et al., 2010, Shiller & Joung Page 4 Climate Institute | www.climate.org 2012}. Climate Alert Volume 27, No. 1

voracity of the methanotrophic re- sponse to the Deepwater Horizon spill took scientists by surprise. Known and unknown bacterial spe- cies were metabolizing methane at rates 10,000 times higher than previ- ously observed for the Gulf of Mexi- co, which has abundant naturally oc- curring seafloor oil and gas seeps and associated microbial communities. The striking capacity of microbes to cope with sudden methane releases- and the unknown factors that may limit this capacity- may have a huge role to play in a warming Earth.

Key Questions For Current Research

What do we know, and more im- portantly, what don’t we know about how methanotrophic microbes re- spond to potential methane releases in the warming Arctic and elsewhere? What are these methane- consuming organisms (and the relat- ed microbes that produce methane)? How do they function biochemically and ecologically in various environ- ments, and what factors limit their methane-consuming activity? How will climate change affect or constrain the microbially-mediated global methane cycle? Are there ways we can help metha- Figure 1. Marine bacteria consumed much of the methane re- notrophic microbes consume gas leased by the 2011 Deepwater horizon well blowout event als required more efficiently to reduce dangerous Notably, for the spe- methane build-up in the atmos- this natural gas banquet was left un- cialized metabolism of methane. The phere? finished, with above-normal methane plume of methanotrophic bacteria levels persisting for at least the fol- could also have been devoured by Bugs, Sources, and Sinks: Methano- lowing year {Crespo-Medina et al., other microorganisms as part of the gens and Methanotrophs in the 2014}. Researchers speculate that oceanic food chain, or even plun- Global Methane Cycle these intense microbial blooms may dered by oceanic . have petered out after using up dis- While methane-eating bacteria Methane (CH4, a single carbon atom solved oxygen in the local seawater, were first described more than a cen- tightly bound to 4 atoms) is or depleting the nitrate or trace met- tury ago, the explosive growth and a naturally-occurring greenhouse gas. All gases with more than three atoms Page 5 Climate Institute | [email protected] Climate Alert

can absorb and re-emit infrared ra- ever, CO2 is so abundant in the at- The global balance of natural pro- diation, contributing to the atmos- mosphere that it already traps most duction and consumption of methane phere’s warming . of the radiation at the wavelengths is dominated by only three groups of Methane’s carbon originally derives that it interacts with. This blocking microorganisms: from photosynthetic sequestration can’t get more intense at the peak 1. the anaerobic methane-producing of atmospheric CO2 by plants. Most spectrum, although increasing CO2 (methanogenic) Archaea, bacteria- methane is the end product of mi- concentration slightly broadens the like organisms found in sediments crobial breakdown of organic mate- absorption span and causes warming beneath the seabed, under fresh- rial in the absence of oxygen, alt- to occur at lower, warmer levels of water lakes and , and hough some is also produced with- the atmosphere. In contrast, because deep in oxygen-free soils; out microbial activity, by thermal methane is present at a much lower 2. their close relatives, the vitally cracking of hydrocarbons. Much of concentration in the atmosphere, important but virtually unknown this production is consumed by oth- each incremental increase has a anaerobic methanotrophic Ar- er microbes before reaching the at- greater warming effect, since there is chaea (ANME), microorganisms mosphere (Figure 2 Overview); the headroom at its unsaturated peak that consume methane in the ab- microbial methane cycle is sence of oxygen, particularly the focus of this article. in marine sediments. ANME Once methane makes it to consume >90% of ocean me- the atmosphere, nearly all of thane (7-25% of global pro- it is oxidized and destroyed duction), but have yet to be within a decade by photo- cultured in laboratories. chemically-produced OH- rad- 3. methane-oxidizing bacte- icals, forming CO2 and water ria (MOB), ubiquitous and vapor. In an indirect forcing water bacteria that consume from methane, both of these methane using oxygen. oxidation products also con- tribute greenhouse effects, These three groups of or- and the resulting CO2 per- ganisms determine the rate sists, at least in part, for many at which methane is pro- thousands of years. In the duced, how much of it is con- long run, the sum of this indi- Figure 2. Global methane cycle overview sumed before reaching the rect forcing from methane-derived atmosphere, and are even responsible CO2 therefore contributes more spectrum to efficiently absorb more for harvesting a significant portion di- warming than direct forcing from radiation. rectly from the air. methane itself. However, on decadal scales decreasing methane emis- Since methane is a short-lived yet The Anaerobic Archaea: - sions has great potential for slowing powerful greenhouse gas, and its esis and Methanotrophy the pace of global warming. concentration in the atmosphere is Counterintuitively, methane’s po- close to a steady state (production Single-celled organisms of the do- tency as a greenhouse gas derives in and destruction nearly balanced), main Archaea are one of the six king- part from its relative scarcity. Green- relatively small changes in emissions doms of life (along with animals, house gas molecules like CO2 and have the potential to change atmos- plants, fungi, protists, and bacteria). methane both prevent heat from pheric concentrations and quickly Formerly considered a subset of bacte- radiating back out to space and affect climate. This is where metha- ria, genomic ancestry analysis now cause the lower atmosphere to re- notrophic microbes play critical roles. groups them as distant relatives tain it in a roughly similar way. How- (Figure 3). They consist of the ex- tremophiles (organisms surviving in Page 6 Climate Institute | www.climate.org Climate Alert Volume 27, No. 1

-consuming their own (in contrast to the ANME, which are aerobic methanotrophs). principally known From the perspective of greenhouse from seafloor sed- gas mitigation, ANME do exhibit an iments {Knittel & extremely useful feature. While their Boetius 2009}. aerobic counterparts, the methane These anaerobic oxidizing bacteria (MOB, found in aer- methanotrophs ated soil and water, see below) can run the same absorb up to about half of metabo- mcrA enzymatic lized methane carbon into their own reaction in re- cellular structures, they also ‘exhale’ verse to obtain CO2, converting a short-lived but pow- energy, usually erful greenhouse gas into a weaker using sulfate from but much longer-lived one that also seawater as an acidifies ocean waters. Figure 3. of Life highlighting methane-consuming and electron acceptor to In contrast, many ANME convert car- methane-producing microbes oxidize methane. bon from methane into , Many ANME live in which reacts with in seawater hot springs, deep sea thermal vents, close proximity with obligate partner and precipitates as solid calcium car- and acidic or alkaline conditions) and sulfate-reducing bacteria (Figures 3 & bonate rock on the sea floor (Figure the anaerobic methanotrophs 4a). 4B). Where methane venting and an- (ANME) and . Methano- Hence, oceanic methane is pro- aerobic methanotrophy have been genic Archaea are responsible for duced by methanogenic Archaea in ongoing, large plates of microbially- producing most global methane. Nei- deeper marine sediments (up to 800 ther methanogenic Archaea nor m beneath the sea floor) where nei- ANME can grow in the presence of ther oxygen nor sulfate is present. oxygen, although they can survive as Then, as methane filters upward dormant seed populations. through to shallower sulfate- Archaeal methanogens produce penetrated sediments (from millime- methane virtually wherever there is tres to 200 m beneath the sea floor), organic material to digest in the ab- more than 90% is consumed by sence of oxygen- in sediments hun- ANME (corresponding to ~7-25% of dreds of meters beneath the seafloor, total global methane production). in lake bottoms and the saturated ANME were virtually unknown until soils of wetlands and ricefields, as the last few decades; indeed, metab- well as in the guts of termites and olizing methane in the absence of ruminant animals such as cattle and oxygen had been thought to be bio- sheep (and to a lesser degree in other energetically impossible until their animals, including humans). discovery. These organisms have still The key enzyme in the final step of not been cultured in the laboratory, Figure 4. Anaerobic methanotrophs con- methane formation during microbial so much remains mysterious about sume >90% of oceanic methane fermentation, methyl-coenzyme M their identity, basic biology, biochem- reductase (encoded by the mcrA istry and genomics. They grow ex- gene), is also central to the metabo- tremely slowly (doubling times of derived calcium carbonate can be seen lism of the methane-producing meth- weeks to months), and incorporate on the ocean bottom, permanently anogens’ close relatives, the methane very little of methane’s carbon into sequestering methane carbon away from the atmosphere rather than con- Page 7 Climate Institute | [email protected] Climate Alert

verting it into CO2. trients like nitrates can limit methane Methane Hydrates, the Clathrate Gun consumption, but the principal con- Hypothesis, and the Microbial Silencer They’re Everywhere: Aerobic Me- straints on methanotrophy are usual- thane-Oxidizing Bacteria ly oxygen concentration and the ‘Tipping points’ occur when one rela- availability of methane itself. tively stable state gradually accumu- Even though the ANME filter out One of the features shared by near- lates a series of small changes until it more than 90% of the methane pro- ly all methanotrophs is that they are becomes unstable, and then transi- duced under the sea floor, substan- highly specialized for growth only on tions rapidly to a very different stable tial amounts of dissolved gas still methane and methanol (‘obligate state (rather than undergoing gradual escape into the sea, and anaerobic methyltrophy’), although some ex- and reversible changes between methanogens also produce methane ceptions with a bit more dietary flexi- states). Such geologically sudden in various terrestrial environments. bility (‘facultative methanotrophs’) changes are known to have happened Once in the water column, sufficient have recently been discovered. While at various points in Earth’s history, oxygen may be present for con- methanotrophic bacteria exist nearly even without the virtually instantane- sumption by aerobic metha- everywhere as ‘seed populations’ in ous atmospheric injection of fossil car- notrophic bacteria. the world’s and aerated soils, bon over the last century. In contrast to the anaerobic meth- and their growth and ability to me- Methantrophic microbes, particularly anogens and ANME Archaea, aero- tabolize methane is not restricted by in the world’s oceans, have played a bic methanotrophs or methane- cold, they only bloom to greater den- vital role in buffering or recovering oxidizing bacteria (MOB) are mem- sity when methane concentrations from at least some of these events. bers of several different families of are elevated. One potential tipping point trigger is conventional bacteria in the phylum Aerobic MOB can grow much more rapid thawing of the vast amounts of Proteobacteria and the more recent- quickly than their anaerobic counter- water-methane ice thought to exist at ly-described phylum Verrumicrobia parts, and incorporate much more of or beneath the ocean floor at low tem- (Figure 3). All of these aerobic the ingested methane carbon into perature and high pressure in solid methanotrophs their metabo- their own cell structures. Measured form. Known as methane hydrates, or lism on the enzyme methane ratios of (CO2 produced)/(methane clathrates, these are thought to be monooxygenase (MMO) to oxidize consumed) range between 0.16 to largely formed from methane accumu- methane (CH4) to methanol (CH3OH) 0.4 (Borjesson et al. 2001), with the lated from biological processes from which energy and carbon are remainder converted into biomass. (methanogenic microbes), although in then harvested for cellular use. The This high ratio of biomass production the Gulf of Mexico and Siberian gas MMO gene is a valuable tool for re- allows MOB to form successful sym- fields, clathrate methane is also de- searchers, who can focus on this biotic relationships with other organ- rived from thermal activity. sequence to identify and analyse isms, particularly mussels, where me- While methane hydrates take the methane-consuming bacteria among thane concentrations are high, such form of icy-looking lumps beneath the complex water or soil microbial ecol- as seafloor seeps. MOB biomass also seabed, even in solid form they are ogies. The subtypes of MMO genes enters the food chain through preda- lighter than water and float upwards if and their association with cellular tion by other microorganisms. De- freed from deposits. Once above the membrane structures are used to pending on the food chain, some of depth limit of the ‘gas hydrate stability divide MOB into Type I and Type II this methane-derived bacterial bio- zone’ (GHSZ), they turn into methane subgroups. mass will also sequester carbon, at bubbles, which in turn may dissolve in To attack the methane molecule, least temporarily. seawater or equilibrate with other sea with its exceptionally tight carbon- water gases before reaching the at- hydrogen bonds, the MMO enzyme mosphere. The GHSZ is determined by requires cofactors like iron and cop- a combination of pressure and tem- per. Depletion of these or other nu- perature in ocean depths, with a lower boundary around 2000 meters below Page 8 Climate Institute | www.climate.org Climate Alert Volume 27, No. 1

the seabed limited by geothermal that large clathrate releases were Meanwhile, Somewhere North of Si- heat. At the other end, clathrates can probably not responsible for the beria… More Bacteria exist up to around 300 meters be- sharp warming at the end of two re- neath sea level along continental cent cold periods-- the Older and The shallow, cold Arctic Ocean may margins, but can be present at depths Younger Dryas, ~14,000 and 11,500 be an exception to the relative re- as shallow as 150 meters underwater years ago, respectively (Sowers sistance of undersea clathrates to an- in cold . Clathrates can also 2006). thropogenic climate change. Here, be stabilized at even shallower Furthermore, most of the global clathrate deposits can exist much clos- depths by overlying solid lids such as hydrate reserve is sufficiently insulat- er to the surface, kept in place both by permafrost. ed from the Earth’s surface climate cold water temperatures, which raise The total store of clathrates re- that large releases in response to an- the GHSZ closer to the surface, and mains uncertain. Estimates derive thropogenic climate change are likely offshore permafrost. mostly from seismic mapping using to be slow. Modelling by Archer and This solid permafrost lid formed high-energy sonar and modelling, but others indicates human-induced when sea level was ~120 meters lower in any case the amounts are vast- --in warming could instigate large-scale during the ice age, but has been grad- the general neighbourhood of 5 tril- methane releases from hydrates be- ually thawing shorewards with sea lion tons of methane. The atmos- neath deep temperate oceans, but level rise following the last glacial max- phere currently contains about 3 bil- these releases would occur over imum 20,000 years ago. Intense lion tons of methane, so even release thousands of years. These studies plumes of methane bubbles rising of a tenth of the clathrate methane in suggest that the comparative slow- from the seabed (‘flares’) have been a short period would have an effect ness of clathrate breakdown would detected by sonar. In deeper waters, on the Earth’s radiation budget allow marine methanotrophs to con- these bubbles both dissolve and ex- equivalent to increasing CO2 tenfold sume much of the methane before it change gases with seawater (reducing (Archer 2007). The ‘clathrate gun reaches the atmosphere, and that the methane content in bubbles). hypothesis’ suggests that sudden direct radiative forcing from clathrate ANME in seabed sediments and MOB warming in the geological past may methane will therefore probably not in the water column are both present have been triggered by such sudden be a major climate driver. in the Arctic, and the rate at which releases (‘methane excursions’), per- However, a chronic global increase they consume methane is virtually un- haps as a result of asteroid impacts or in MOB activity will have major affected by cold temperatures. other physical events like submarine effects on warming seas, which con- While methane dissolved in deep landslides destabilizing clathrate de- tain decreasing amounts of dissolved water can still surface and escape into posits. oxygen. Aerobic methanotroph me- the atmosphere by gas exchange, sev- Did the ‘clathrate gun’ go off to end tabolism would consume even more eral unique properties of the Arctic recent glacial periods? Warm eras oxygen, exacerbating hypoxia from Ocean limit this. Ice cover can block virtually always show higher levels of warming. CO2 produced by MOB like- surface gas exchange, and many large atmospheric methane. However, this wise contributes to ocean acidifica- rivers pour into the Arctic, creating a can be an effect of warming driven by tion. The scale of the contribution buoyant fresh water barrier floating other factors rather than a cause; for from the poorly-understood ANME, on denser saltier water and preventing instance, warmer often lead which can sequester methane carbon methane-saturated water mixing from to large increases in methane- as carbonate rock, remains an open below. Modelling studies indicate that producing wetlands. question. MOB can oxidize available dissolved Methane produced by wetlands can methane completely over ~50 years, be distinguished from marine clath- with deep water eventually returning rates by isotopic analysis of deuteri- to the Atlantic (Elliot et al 2011). um/hydrogen ratios. Isotope studies However, the ability of ice and fresh- of ice cores from Greenland show ened surface waters to block methane -saturated deep water from atmos- Page 9 Climate Institute | [email protected] Climate Alert

pheric exchange is finite. Rapid Arc- by ANME, with the carbon retained they bind methane with low affinity, tic warming is forcing ice cover to within the seafloor, and most of the they thrive in conditions where con- retreat quickly, and increased storm remainder digested by MOB in the centrations are relatively high and frequency causes more mixing and water column. These analyses con- consume large amounts of methane dilution of the freshwater layer, al- clude that clathrate methane re- before it can reach the atmosphere. lowing more methane to escape leased due to anthropogenic warm- (Shakhova et al 2014). Better under- ing is not likely to be a major contrib- Eating Thin Air: Upland Soil Metha- standing of the factors that truncat- utor to global warming over the next notrophs ed the Deepwater Horizon metha- 100 years. notroph bloom is also needed. Could However, these initial studies do The other functional category of MOB depletion of oxygen and trace predict that increased bacterial me- MOB species is the ‘high affinity oxidiz- metals (iron/copper) also eventually tabolism from rising clathrate me- ers’, which provide the ‘soil sink’ for limit the methanotroph response in thane could significantly deplete oxy- atmospheric methane. Other MOB the Arctic? How might the rest of gen and lower pH in the Arctic basin, and ANME capture and oxidize CH4 the polar sea food chain respond to to the detriment of the ocean ecosys- where it is present in higher concen- sustained methanotroph blooms? tem. Since these are relatively early trations within soil on its way up from Parts of the Arctic Ocean (in partic- modelling studies of complex pro- localized sources . Methane is present ular the East Siberian Sea) are so cesses at the intersection of ocean- in the atmosphere at very low concen- shallow that methane bubbles from ography, geology and biology, the trations (less than 2ppmv), but high- the seabed can arrive at the surface scientific understanding of these in- affinity oxidizers in soil are thought to relatively intact. While it is clear that teractions may change quickly. consume upwards of 20-60 million methane releases are ongoing, in tons of atmospheric methane annual- particular where the edge of the The Microbial Methane Cycle in Soil ly, making up 4-15% of the global me- undersea permafrost ‘lid’ is thawing, and Freshwater Sediments thane sink). at present much of this seems to be The activity of these high-affinity in response to post-ice age sea level Like marine methanotrophic bacte- MOB can be detected in most of the rise rather than anthropogenic ria, aerobic soil methanotrophs are world’s soils using molecular and bio- warming (Portnov et al., 2013, nearly all highly specialized to use chemical methods, but these organ- Portnov et al., 2014). Isotopic stud- only methane/methanol as a source isms have yet to be identified or cul- ies of atmospheric methane over of energy and carbon. These bacteria tured as pure populations in the labor- northern Europe also show that are present, at least as ‘seed’ popula- atory, and their identity remains mys- clathrate methane has yet to make a tions, in virtually all the world’s ter- terious. While they are able to harvest major contribution, with most of the restrial soils (including your back gar- methane at very low concentrations, methane that makes it to the atmos- den), but different soil environments they appear to grow very slowly, sur- phere over Northern Europe appear- support very different bacterial com- rounded by thousands of varieties of ing to derive from gas fields or wet- munities and methane-consuming other soil bacteria, possibly relying on lands (Fisher et al., 2011). capacities. some for metabolic services analogous Several studies have modelled how Soils and sediments with high con- to the symbiotic partnership between projected warming over the next centrations of methane (up to ~100 ANME and sulfate-reducing bacteria. century may affect releases of clath- ppm), such as wetlands, ricefields Identifying the responsible high- rate methane by lowering the GHSZ and , tend to support dense affinity organisms for intensive study is boundary in the Arctic Ocean populations of ‘low-affinity oxidizers’. one of the holy grails of methanotroph (Biastoch et al., 2011; Elliot et al., These include most of the MOB spe- studies. 2011). Models suggest that most of cies that have been successfully cul- Although high affinity metha- the methane that dissolves in satu- tured in the laboratory and about notrophs appear to be ubiquitous in rated sediment could be consumed which we understand most. Although soils, not all soils are equal. The key factor for methanotrophy in many Page 10 Climate Institute | www.climate.org Climate Alert Volume 27, No. 1

soils seems to be water saturation, The water table affects the balance of particularly those underlain by perma- although availability of cofactors like and methanotrophy frost, are increasingly becoming recog- copper or iron and exposure primarily by affecting the boundary of nized as critical. These soils often con- can also be important. Saturation oxygen availability beneath which tain very high concentrations of car- reduces oxygen availability, which anaerobic methanogenic microbes bon because of the differences in the both limits aerobic methanotrophy thrive on . balance of plant growth and microbial and encourages anaerobic methano- degradation. genesis. Although plants grow slowly Thus, soils, well- in arctic and subarctic condi- drained by tree roots, are tions, much of the organic excellent methane consum- material created is buried and ers. Disturbed or irrigated sequestered in permafrost, agricultural soils perform where virtually no microbial much more poorly. According breakdown occurs. High- to one calculation, the con- latitude terrain has therefore version of natural soils to been acting as a vast carbon agricultural use has reduced storage reservoir for tens of the global methane soil sink thousands of years, with per- by 71% (Smith et al., 2000). mafrost carbon estimates run- Consideration of this vital ning above 1,700 petagrams atmospheric service needs to (1.7 trillion tons, or about be incorporated in land-use twice the current total atmos- management and planning. pheric carbon). This is changing rapidly as Future of Terrestrial Metha- the Arctic warms (Figure 5). notrophy Current estimates predict re- lease of ~170 billion tons of A number of studies have carbon from permafrost thaw addressed how the microbial by 2100 (MacDougall et al. methane cycle may be affect- 2012), putting a substantial ed by a more carbon-rich dent in the Earth’s remaining atmosphere and warming cumulative climate (Nazaries et al., 2013; of 440 billion tons of Turetsky et al., 2014). Wet- manmade CO2 for staying un- lands constitute by far the der a 20C temperature rise. largest natural source of at- Much of the high Arctic con- mospheric methane, and are sists of or muskeg, a thin expected to increase in ex- layer ‘active zone’ of season- tent with warming, both in ally-thawed saturated soil the tropics and at higher lati- overlying permafrost. Warm- tudes. The activity of me- Figure 5. Projected thaw in Siberia ing tends to increase the thane-producing Archaea is strongly thickness of this thawed active zone, dependent on water table level and While tropical and subtropical wet- releasing greater amounts of stored temperature (in contrast to MOB me- lands have long been assumed to be organic material for anaerobic fermen- thane-consuming activity, which is the largest natural sources of atmos- tation and methane production by relatively temperature-insensitive). pheric methane, high-latitude soils, methanogenic Archaea, or, depending largely on water saturation, MOB ac- Page 11 Climate Institute | [email protected] Climate Alert

tivity producing CO2. phere. One exception may be me- identified as species or grown in cul- Many analyses of global warming thane in coal mine ventilation, a ma- ture, limiting the application of the have assumed that arctic environ- jor emissions source in many coun- most powerful biochemical and ge- ments would act as a larger atmos- tries. At laboratory scale, open biore- nomic research tools. Laboratory engi- pheric in the future, by actors containing methanotroph cul- neering and large-scale deployment to virtue of enjoying a longer growing tures can remove 70-90% of me- combat future methane releases season and becoming more photo- thane at concentrations typical of seems a distant prospect, or worse, a synthetically productive. However, coal mine (Jiang et al study in unforeseen consequences other studies suggest that any gains 2010). more suited to a Hollywood disaster in Arctic carbon storage from a long- Methanotrophic bacteria are al- movie. Attempts to artificially modify er growing season may be more ready widely employed in various soil or water microbes for introduction than offset by increased greenhouse bioremediation processes, particular- into biomes near the base of environ- forcing from methane emissions. ly for breaking down toxic halogenat- mental food chains should be treated Thus, high latitude wetlands can act ed hydrocarbons in chemical waste with extreme caution. as both a net carbon sink, and a net . However, obtaining a suffi- In practice, field applications of engi- source of greenhouse gases (Friborg ciently dense bloom of metha- neered methanotrophs are likely to et al., 2003). notrophs to oxidize these toxic com- remain very limited. Nearly all existing How Arctic warming affects wet- pounds usually involves providing methanotrophs are ‘obligate methyl- land extent and soil saturation is key extra methane as well as oxygen, so trophs’, meaning they can only grow for the methanogenesis/ these applications may not actually on methane or another single-carbon methanotrophy balance. The hydrol- reduce emissions. compound, methanol. Large quantities ogy and landscape changes induced and sewage treatment fa- of some species might be grown under by permafrost thaw are too complex cilities are also major methane laboratory conditions, but released to cover here (Walter et al., 2014). sources, contributing ~55 million tons into the environment in the absence Thawing results in a variety of sur- annually, or around 10% of atmos- of enriched methane sources they face structures like taliks, wetlands pheric methane. These facilities have would be outcompeted by other soil and thermokarst lakes, but can also long intentionally utilized endoge- bacteria, and would be unlikely to re- lead to drainage of surface water/ nous MOB, and research to further spond to increases more ably than soils if a permafrost basement is optimize methanotroph activity is endogenous methanotrophs already punctured. Strategies for permafrost ongoing. The same considerations as present as seed populations virtually stabilization with methanotroph in wetlands often apply, with oxygen everywhere. benefits are discussed below. often a limiting factor. Forced air While the anaerobic methanotrophs sources can greatly increase methane (ANME) found in marine sediments Managing microbes for methane consumption and reduce emissions, play a vital role in the global methane mitigation but the the combination of , and have the attractive ability to with high landfill methane concentra- permanently sequester methane’s car- Human activities now produce the tions can introduce unacceptable bon in the form of carbonate precipi- majority of atmospheric methane. explosion risks (Lopez et al., 2013). tates rather than releasing a portion as Methanotrophs are vital for limiting CO2, they also have several properties emissions from human sources such Restoring Ecologies for Optimal Me- that are likely to make them difficult as landfill, sewage treatment and thane Mitigation to deploy. ANME have thus far been agriculture. Other sources, such as impossible to culture in the laboratory, those from fossil fuel extraction, The basic biology of methanotrophs and often exist in obligate relation- transport and industry, are not gen- still holds many mysteries. Key cate- ships with other microbial species or erally accessible to microbial mitiga- gories of organisms, like ANME and communities such as sulfate-reducing tion before they reach the atmos- high-affinity MOB, have yet to be bacteria, greatly complicating manipu- lations. Their extremely slow growth Page 12 Climate Institute | www.climate.org Climate Alert Volume 27, No. 1

rates, with doubling times of weeks and demand is expected to rise by tate. Some of these non- to months (compared to ~20 minutes 65% over the next two decades with methanogenic kangaroo gut acetogens for many bacteria) also makes for the world’s rising population. are already known to be present at ponderous engineering prospects. Ricefields annually emit between 6% low levels among the gut flora of do- Learning more about metha- and 19% of total anthropogenic me- mestic cattle (Godwin et al., 2014 ). notrophic microbes remains vitally thane, but the amount produced var- Theoretically, methane emissions from important despite the barriers to di- ies widely with regional conditions cattle, goats and sheep might be driv- rect deployment for climate mitiga- and practices. en down by encouraging the preva- tion. Understanding the ecology of Studies have shown that one such lence of these naturally-occurring gut naturally-occurring methanotrophs practice, intermittent drainage of acetogen bacteria at the expense of will be essential for predicting green- paddies, can reduce methane produc- methanogenic Archaea. Understand- house forcings from anticipated tion by 40-48% without decreasing ing why these microbes succeed in clathrate methane releases as oceans rice yields (Ma & Lu, 2010, Ma et al., kangaroo could eventually provide warm. Knowledge of methanotroph 2013). Intermittent drainage achieves strategies for adapting domestic rumi- ecology will also be key for assigning at least two things: it tips the balance nant digestion. values to services from away from establishing anaerobic particular habitats and minimizing methanogens in saturated soil and costly future mistakes. As mentioned towards aerobic methanotrophs in above, more than half of the global aerated soil. Exposure to air also re- Aerobic methanotrophic bacteria capacity of the high-affinity soil sink generates iron and sulfate ions from exist virtually ubiquitously as seed for atmospheric methane has been reduced forms, allowing other anaer- populations in almost all soils and wa- lost by agricultural conversion of pre- obic bacteria to compete with meth- ters, both fresh and salt. Their capacity viously undisturbed land, particularly anogens for key substrates. to convert methane to biomass or CO2 . Methane mitigation provides is limited by the availability of their one more reason to aggressively Ruminant farming energy/carbon source (methane or combat . methanol), oxygen, nitrate and trace Understanding and tweaking the Domestic cattle, sheep and goats nutrients such as iron or copper. workings of methanotrophs and are a major anthropogenic source of In many terrestrial environments, methanogens in major anthropogenic methane, contributing about 90 mil- the level of the water table is the criti- sources like landfills and rice fields lion tons per year or ~17% of the cal factor determining the balance be- could also provide very large reduc- global atmospheric source (wild rumi- tween methane production (by anaer- tions in methane emissions. The very nants are a small factor, contributing obic methanogenic Archaea) and me- large emissions from non-managed only about another million tons). Ru- thane consumption/oxidation by aero- natural sources might also be mitigat- minant methane emissions result bic methanotrophs. Saturated ed, with potential increased removal from an ancient symbiosis with an- soils host anaerobic methanogens; of methane directly from the atmos- aerobic gut microbes, which are an drier aerated soils contain metha- phere. An intriguing prospect of essential part of the ruminant diges- notrophs. There is a hierarchy among achieving this through addressing an tive strategy. different soil , with upland ancient human environmental impact While methanogenic Archaea domi- forest soils capable of the largest is discussed below. nate in the guts of ruminants, some amount of methane oxidation. wild herbivores such as kangaroos Non-saturated soils contain bacterial Ricefields possess similar gut anatomy but pro- communities that not only oxidize me- duce little or no methane, with diges- thane released by underlying organic Rice production, typically in semi- tion services provided by other clas- fermentation, but actually consume artificial wetland environments, is an ses of anaerobic bacteria leading to methane directly from air and are re- important part of the food supply, alternative end products such as ace- sponsible for about 4% of the annual atmospheric methane budget. Differ- Page 13 Climate Institute | [email protected] Climate Alert

ent soil ecotypes provide this service anogenic environments. with large herbivore densities compa- with different efficiency; boreal and Are there other avenues for en- rable to contemporary African savan- temperate forests and upland grass- couraging methanotrophy or reduc- nahs (Zimov et al., 2012 ). The change lands are the most effective (Dalal et ing methanogenesis from wetlands from to today’s relatively al., 2008). Remarkably, deforested without increasing the human foot- unproductive moss-covered boggy areas can recover optimal atmos- print on valuable natural areas? Re- wetland and forest coincided pheric methane oxidation capabili- searchers in northeast Siberia are with the disappearance of large herbi- ties within a few decades following evaluating a radical strategy whose vores such as mammoths and woolly reforestation (Nazaries et al., 2011). principal goal is keeping sub-tundra rhino as well as the decline or local Methane mitigation can be added to permafrost carbon frozen by restor- extirpation of extant species like musk the long list of valuable carbon se- ing an ancient ecosystem. As a side oxen and bison. questration and ecosystem services effect, their program could tilt the The cause of the Pleistocene large provided by forests. balance away from methanogenesis herbivore extinctions remains contro- and towards methane consumption. versial. Rapid warming at the end of Breaking Bubbles In the rapidly warming Arctic, there the ice age contributed to changes in is deep concern about methane re- diet and habitat, but many researchers As described above, methane re- leases from organic material in thaw- argue that overhunting by humans leased at depth dissolves in the wa- ing permafrost loess/yedoma arriving on the steppes with new tech- ter column, and can be efficiently (organic-rich soils with high ice con- nologies was a critical factor. Regard- oxidized by methanotrophic bacte- tent), as well as terrestrial gas hy- less of the cause of the extinctions, ria. However, in shallow Arctic seas drate deposits trapped beneath a their disappearance has been associat- and lakes, large bubbles can escape destabilized permafrost ‘lid’, the like- ed with the ensuing steppe-tundra directly to the atmosphere, evading ly cause of last summer’s crater ap- transition (Zimov et al., 1995), with oxidation by methanotrophs. In lo- pearances on the Yamal peninsula. reduced pressure leading to calized regions of high bubble re- The degree to which thawed organic prevalence of mossy wetland and bog- lease, it may be possible to encour- material produces methane, and in gy muskeg sparse low forest. age greater solvation in the water turn how much methane is con- If late Pleistocene overhunting was column by simple physical methods. sumed before reaching the atmos- indeed the cause of large herbivore Covering sediment with a screen or phere, depends largely on the water extinctions, then high arctic muskeg/ other porous material to reduce the table. Permafrost-underlain terrain bog is an early but large-scale feature size of bubbles will increase the sur- undergoes complex transitions with of the human planetary footprint. In face-to-volume ratio and encourage gradual thawing, producing thermo- 1989, the Zimov group, based at the dissolution, increasing availability for karst and thaw lakes and associated Northeast Science Station in Chersky, methanotrophic digestion (Stolaroff wetland which can also drain when began a long-term, large-scale et al., 2012). the ‘floor’ of underlying ice layers ‘Pleistocene Park’ experiment to see if disappears (Walter et al., 2014). this footprint can be removed (Zimov Reverse Geoengineering the Mam- In much of the high arctic in both 2005), but not by cloning mammoths. moth Steppe Siberia and Canada, permafrost is In a 6 square mile enclosure in one of overlain by muskeg or bog. However, the coldest regions on Earth, they Wetlands are the largest natural this appears to be a relatively recent have begun reintroducing extant cold- sources of methane, but in many geological feature. Up until about adapted large herbivores like Yakut regions they also provide essential 14,000 years ago, during both colder horses, musk oxen, reindeer, moose, habitat and ecosystem services. Sim- ice age stadial periods as well as wood bison and wapiti (elk) to see if ple ditching to drain wetlands may warmer interglacial periods, the Sibe- the productive grassland steppe can also be counterproductive, as ditch- rian steppe was highly productive be restored. Preliminary results are es themselves can be highly meth- grassland (the ‘Mammoth Steppe’), mixed, with poaching and adaptation- related herbivore mortality, but con- Page 14 Climate Institute | www.climate.org Climate Alert Volume 27, No. 1

version to well-drained, highly pro- effect of drying out soil, creating a greenhouse gas. Recent progress in ductive grassland occurred surprising- larger niche for methane oxidizing understanding aspects of the biologi- ly quickly (Zimov et al., 2012). bacteria. cal methane cycle underlines how The principal goal of this project is The ‘Pleistocene rewilding’ aspect much we still don’t know. not to create a nature reserve, but is of the experiment remains controver- Research priorities include: a serious attempt to test a form of sial, but the scientific analysis being  Identification and laboratory cul- reverse geoengineering for com- applied is rigorous. In principle, the ture of high affinity metha- bating warming. By restoring the strategy could be applied to large notrophic bacteria from soil. Isola- Pleistocene grassland steppe state areas of northeast and North tion and culture will allow bio- from Holocene bog/ chemical and genomic analysis muskeg, they hope to to understand how these or- address one of the most ganisms capture and consume pressing problems in methane at atmospheric con- contemporary climate centrations. change: carbon (and me-  Identification and labora- thane) emission from tory culture of anaerobic thawing permafrost. methanotrophic Archaea from Light-coloured grassland marine sediments. Anaerobic has a much higher albe- methanotrophy remains virtu- do than dark mossy bog ally a black box despite its im- or scrub taiga, reflecting portance in the global me- more solar radiation in thane cycle. Laboratory cul- summer. In winter, her- ture will allow detailed analy- bivores disturb snow sis of biochemical mechanisms cover while foraging, al- and the limitations on growth lowing deeper penetra- and . tion of cold and perma-  Quantifying anaerobic frost reinforcement methanotroph activity in situ (Figure 6). in marine sediments, in partic- The effects on microbial Figure 6. Restoration of the Mammoth Steppe: cCan large herbivore ular their ability to permanent- methane ecology are also reintroductions stabilize permafrost and reduce methane emissions? ly sequester methane hydrate- robust. Stabilizing perma- derived carbon, and understand- frost at shallower soil depths reduces America. Coincidentally, in April 2015 ing the complex relationships they both the bank of organic material Alaska saw the reintroduction of the have with other microorganisms. available to methanogenic archaea first wild Wood Bison herd in over a  Identifying factors limiting aerobic and the volume of their saturated soil century, a subspecies that had and anaerobic methanotroph niche. Methanogens also produce neared extinction in North America. growth and metabolism in marine methane much more slowly at colder The scale of risk from thawing perma- and soil ecologies, particularly in temperatures in contrast to MOB, frost carbon demands ambitious ap- the Arctic whose metabolism is relatively insen- proaches.  Quantifying soil methanotrophy in sitive to cold. Draining tundra soils different ecosystem types for opti- has been experimentally shown to Conclusion mal land-use planning, especially reduce methane and CO output 2 in the Arctic (Merbold et al., 2009). Grass roots Methane-consuming microbes man- penetrate much more deeply than age much of the global budget of the  Continuing to identify aerobic those of bog mosses, and have the Earth’s second-most important methanotrophs from different bacterial lineages, particularly fac- Page 15 Climate Institute | [email protected] Climate Alert

ultative methanotrophs, which Letters, vol. 38 roo foregut by stable isotope probing. can use alternative energy/ ISME J.;8(9):1855-65. doi: 10.1038 carbon sources in addition to Borjesson et al., (2001) Methane methane/methanol. The role of oxidation in two Swedish Landfill Jiang et al (2010) Methanotrophs: these organisms in the global Cover Soils Determined with the Use Multifunctional bacteria with promis- methane budget remains un- of 13C/12C Isotope Ratios. J. Environ. ing applications in environmental bio- known, and they may be more Qual., 30, 369−376. engineering. Biochemical Engineering suitable for bioremediation and Journal 49, pp 277–288 mitigation applications than obli- Bousquet et al., (2006) Contribution gate methanotrophs. of anthropogenic and natural sources Kessler et al., (2010) A Persistent Oxy- to atmospheric methane variability gen Anomaly Reveals the Fate of Footnote Nature Vol 443, pp. 439-443 Spilled Methane in the Deep Gulf of 1. Comparing effects of different doi:10.1038 Mexico. Science Vol. 331 no. 6015 pp. greenhouse gases is complicated 312-315 by their differing atmospheric Crespo-Medina et al., (2014) The rise DOI: 10.1126 lifespans (~9 years for methane and fall of methanotrophy following versus centuries-to-millennia for a deepwater oil-well blowout. Nature Kimes et al., (2014) Microbial trans- CO2). This calculation is based on Geoscience, 2014; DOI: 10.1038/ formation of the Deepwater Horizon a given quantity of methane ngeo2156 oil spill—past, present, and future per- having ~30 times stronger spectives. Front. Microbiol., doi: warming influence over a 100- Dalal et al., (2008) Magnitude and 10.3389/fmicb.2014.00603 year span than CO2. Its relative biophysical regulators of methane influence is about 80 times emission and consumption in the Knittel & Boetius (2009) Anaerobic stronger on a 20-year basis, so Australian agricultural, forest, and oxidation of methane: progress with cutting its emissions is especially submerged landscapes: A review. an unknown process. Annu Rev Micro- critical to slowing warming over Plant Soil 309, 43−76 biol. 63:311-34. doi: 10.1146/ the next few decades (IPCC, annurev.micro.61.080706.093130. 2013). Elliot et al., (2011) Marine methane Lopez et al., (2013) Biotechnologies for cycle simulations for the period of greenhouse gases (CH4, N2O, and early global warming, J. Geophys. References CO2) abatement: state of the art and Res., 116, G01010, challenges. Appl Microbiol Biotechnol doi:10.1029/2010JG001300. Anisimov (2007) Potential feedback 97:2277–2303 DOI 10.1007/s00253- of thawing permafrost to the global 013-4734-z Fisher et al., (2011) Arctic methane through methane sources: Isotopic evidence for atmos- emission. Environmental Research Ma & Lu (2010) Regulation of microbi- pheric inputs, Geophys. Res. Lett., 38, Letters Volume 2 Number 4 al methane production and oxidation L21803, doi:10.1029/2011GL049319. by intermittent drainage in rice field

Archer (2007) Methane hydrate sta- soil. FEMS Microbiol Ecol 75 (2011) Friborg et al., (2003) Siberian wet- bility and anthropogenic climate 446–456 lands: Where a sink is a source, Ge- change. Biogeosciences, vol. 4, pp. ophys. Res. Lett., 30, 2129, 521-544 Ma et al., (2013) Dry/Wet Cycles doi:10.1029/2003GL017797, 21. Change the Activity and Population

Biastoch et al., (2011) Rising Arctic Dynamics of Methanotrophs in Rice Godwin et al., (2014) Investigation of Ocean temperatures cause gas hy- Field Soil. Applied and Environmental the of carbon drate destabilization and ocean acid- Microbiology p. 4932–4939 Volume 79 dioxide and hydrogen in the kanga- ification. Geophysical Research Number 16

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The Climate Institute is a non-profit, Climate Alert 501 (c) (3) charitable, educational organization. Published periodically by the Climate Institute It receives financial support from © 2015 government agencies, foundations, corporations and ISSN 1071-3271 associations, environmental and research Sir Crispin Tickell, Chairman organizations, and individuals. John C. Topping, President Jeeihn Lee, Editor-in-Chief Bryan Robinson and Front cover image: Arctic sunset, taken by Kathryn Hansen, NASA Back cover image: Polar bears, taken by Jessica Robertson, US Geological Survey Chiamaka Kenneth Ogwuegbu, Assistant Editors Editor’s note: For all citations and references, see the electronic version of this newsletter at www.climate.org