Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | , 3 Chemistry and Physics Discussions , S. Elliott Atmospheric 2 , M. Reagan 1 , D. Bergmann 1 26478 26477 , P. Cameron-Smith 1 2 ), (2) to be well mixed because of its long lifetime, and (3) to have sources 2 This discussion paper is/has beenand under Physics review (ACP). for Please the refer journal to Atmospheric the Chemistry corresponding final paper in ACP if available. Lawrence Livermore National Laboratory, Livermore, CA,Lawrence USA Berkeley National Laboratory, Berkeley, CA,Los USA Alamos National Laboratory, Los Alamos, NM, USA (and perhaps other smallcrystals. molecules) Sub-seabed are lodged within is the primarily lattices produced of water by clathrate microbial and thermogenic ozone increases. 1 Introduction Methane is widely understood(after (1) as CO the secondin most consequential the greenhouse gas known that as may hydrates) are be solid released crystalline compounds in in a which methane warming gas . molecules Methane clathrates (also methane as a fully interactiveary tracer conditions) along (with with emissions the ratheroxide. main The than chemical results reactions concentration show for bound- that methane, such ozone,trations Arctic and non-uniformly, clathrate and nitrous emissions that increase increases methane in concen- in surface polluted ozone regions. concentrations We are also greatest find that the interannual variability in surface methane and temperatures could lead to dissociationocean of and the subsequently the clathrates . and This releaseparts is methane of of particular into the importance the Arctic in Ocean,depths the since shallow of clathrates around are 300 m. expected In toCommunity this start Earth paper, we outgassing System present abruptly Model a at (CESM1) comparisonadditional for of methane present-day simulations conditions from emissions the with from anda without state-of-the-art a ocean plausible sediment model. clathratephysical ocean The release and CESM we scenario model added includes a based fast a atmospheric on fully chemistry interactive mechanism that represents A highly potent greenhouseposits gas, methane, containing is a locked inboth mixture the ocean of solid sediments water phase andder as and underneath ice-like high gas de- pressures regions. (mostly and Clathrates methane) low are called temperatures. stable In un- clathrates a in warming climate, increases in ocean and G. Moridis 1 2 3 Received: 4 September 2012 – Accepted: 23Correspondence September to: 2012 S. – Bhattacharyya Published: ([email protected]) 5 OctoberPublished 2012 by Copernicus Publications on behalf of the European Geosciences Union. Abstract Tropospheric impact of from clathrates in theRegion Arctic S. Bhattacharyya Atmos. Chem. Phys. Discuss., 12, 26477–26502,www.atmos-chem-phys-discuss.net/12/26477/2012/ 2012 doi:10.5194/acpd-12-26477-2012 © Author(s) 2012. CC Attribution 3.0 License. 5 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | C 13 δ ett and Archer, ff ect of orbital variations. ff ) (Klauda and Sandler, 2005; Gor- 4 ) in methane bubbles (Bu Tg(CH 4 6 26480 26479 10 × ) over the subsequent two centuries even if there 4 Tg(CH 6 10 ) (Milkov, 2004; Archer et al., 2009) at the lower end, ected by Atlantic inflow where methane clathrates are 4 × ff Tg(CH 6 ) in the century following the appearance of methane plumes, with -driven ocean circulation changes (Lunt et al., 2010) could have 4 2 10 ) (Maslin et al., 2010), with a similar amount in the Antarctic (Wad- 4 × 3) − Tg(CH et al., 2012; Archer, 2007). Any release of that methane is then expected to 6 ff 10 × A recent study (Reagan et al., 2011a,b) estimates the methane released into the Worryingly, there have been recent observational studies, mainly confined to the Arc- The potential impact of methane clathrates is shown in several paleoclimate stud- water column from methane clathrates1600 over to 8000 the Tg(CH entire Arctican basin additional will 4300 be to in 22is the 000 Tg(CH no range further increasefrom in a model ocean sensitivity bottom studyon based temperature. on the In one global this of these atmosphere paperatmospheric scenarios, using we and chemistry analyze present the component its and results state-of-the-art impact fullynized CESM active in model physical five ocean. with sections. The an paper Section interactive is 2 orga- gives the details of models, method and data used ship. In another studyperatures (Biastoch under et a al., projected 2011), warmingbe an scenario analysis on suggests of the that Arcticmost shallow the bottom strongest sensitive regions water impact to tem- a will dissociation,depletion with in consequences the for water ocean column (Elliott acidification et and al., oxygen 2011a). have observed substantial methanethe Spitsbergen gas continental plumes slope at emanatingdict depths of from the 150–400 m, first the which evidence seaflooralthough is of where a along models study clathrate pre- (Fisher release etfound will that al., such be 2011) methane plumes seen of have theing not (Reagan yet of isotopic and reached methane evidence the from Moridis, of atmosphere. the Extensive methane 2009), et vent- East in Siberian al., Arctic Arctic 2010), air Shelf with hasproducing also large bubbles been increases reaching observed in (Shakhova the atmospheric atmosphere methane concentration through as the measured shallow on the ocean and resulted from destablizationstween triggered the by climate nonlinear and interactions the be- cycle that modulatedtic the region, e observing fluxes of methanebe into from the clathrates ocean and/or and relic atmosphere permafrost. that Field are investigations likely (Westbrook to et al., 2009) (specifically the Paleocene and Eocene periods spanning 59 to 50 million years ago) over thousands of years(Lunt rather et al., than 2011) as it is a postulated single that the catastrophic multiple rapid event. warmings In during the another Paleogene study 2009) which postulate the rolescale of global methane warming clathrate in destabilizationexcursion the in Earth’s in triggering climatic the large- history, geologic asepochs evidenced record. during by Notable the the Permian-Triassic among carbon Paleocene-Eocene boundary these thermal (about incidents maximum 252 were (aboutpothesized million the that 55 years warming CO ago) million andamplified years the the ago). Paleocene-Eocene It thermal2007; has maximum Archer been clathrate et hy- destabilization al., 2009), (Archer, although such a release might have occurred chronically produce that isstratospheric enhanced water by vapor, an andtherein). increase carbon in methane dioxide lifetime, (Isaksen ozone, et al., 2011,ies and (Lunt references et al., 2010, 2011; Lamarque et al., 2006, 2007; Archer, 2007; Archer et al., to an upper estimatenitz of and about Fung, 74.4 1994),2004). plus The 2 Arctic0.53 region alone isham estimated et to al., 2012). haveArctic There that a could are clathrate impart alsolarly reservoir methane other permafrost, of to potentially the about the large East(Stolaro atmosphere Siberian sources in Arctic of a Shelf, methane warming northern in scenario, lakes, the particu- rivers, and wetlands lease of methane clathrates2008, (Elliott 2009; et Reagan et al.,2000). al., 2010, A 2011a; vast 2011a; quantity Archer, Reagansediments 2007; of and on methane Archer Moridis, continental clathrate et margins 2007, isbetween al., and estimated (0.5 2009; in to Kennett permafrost be et regions. trapped al., Precise in estimates the vary marine processes. Sea floor perturbations of temperature and pressure can then lead to re- 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | to the reg- 1 − ) yr 4 ). x ects of non-methane -line chemistry model ff . The specific version ff 2.5 degrees for the at- C per century at 350 m, ◦ × 5 + ects of methane (Collins et al., ff C per century below 600 m. Specifically, for ◦ erence is within the emission uncertainties. 1 26482 26481 ff + http://www.cesm.ucar.edu/ HYDRATE code (Moridis et al., 2008) used to generate our ocean + ), carbon mono-oxide (CO), and nitrogen oxides (NO 4 C per century at 400–600 m, and ◦ The predicted emissions are not a simple function of the warming. Rather, in re- The TOUGH The chemical reaction set in CAM-chem (Lamarque et al., 2012) was replaced with 3 followed by a slow decline,(see such that Fig. it 1). can In be orderrepresentative crudely to of approximated do by one our a sensitivity of step+ study function the we higher selected an emissionour emission scenarios: simulation rate with that enhanced was Arcticular emissions we sources added in 139around Tg(CH our 10 present-day % control. more than Note we thatvert intended this from because is the CESM actually provided uses emission bi-linear grid interpolationespecially to to with the con- point atmosphere sources, grid, but which this is non-conservative, di from 300 m to 700 m. sponse to gradual warming ata the few sea-floor, decades there while is the noway heat significant back propagates methane into up release the for to sediment the and the sea-floor. methane There works is its then an abrupt increase in the emission rate, hibitor . The code wasdeposits used with to a simulate uniform disperse, initialestimated low-saturation clathrate (stratigraphic) saturation global of average 0.03, saturation reflectingsimulated the for a high such 1-D end domain deposits. of describingand the At the was each initialized sediment at depth column thermal, from and chemical,temperature. the and Using location hydrostatic seafloor plausible equilibrium physical it downward, parameters for for eachtions, the depth the sediments and 1-D and model for the wasthe simula- integrated Sea over the of Arctic Okhotsk basin using (Reagan et a al., 4-min 2011a,b) ETOPO2 and bathymetric grid, at 50 m depth intervals methane (CH methane flux scenarios simulatedgeologic multiphase media. flow It and includedand coupled transport described mass in the and clathrate-bearing full energy phase transport behavior within of porous water, media, methane, solid clathrate, ice, and in- set, and included tests of the chemical response to perturbations in the emission of make the multi-century simulations presentedformance in of this this work “fast” feasible. mechanism The was chemical validated per- by comparison with the full reaction a simplified version of the chemical(Rotman reaction et set al., of 2004), the which IMPACT was o sphere designed to and, simulate both most thea troposphere critically and concentration strato- for boundary condition. this“full” The work, specific IMPACT reaction reaction to set set, handlephotolysis is comprising reactions methane a (Cameron-Smith just “fast” emissions et version 28 al., of ratherhydrocarbons species, 2006) and the than in 52 halogens which are thermal the ignored e reactions in order and to 19 reduce the computational cost and the sea-ice component, andatmospheric CAM-CHEM chemistry with component. amosphere The and “fast” resolution approximately chemistry was one mechanism degree 1.9 radiation for for code the to the ocean. include We2006). the modified the short-wave atmospheric absorption e We performed oura simulations state-of-the-art with the globalocean, CESM climate sea-ice, model biogeochemistry, model and (Gentand atmospheric that et documentation chemistry includes al., are components. interactive 2011), availableused The in at code atmosphere, which this is land, studytion is used a was modified B2000CNchem, version which4 of uses (CAM4) CESM the for 1.0 Community the beta Atmosphere atmosphericCarbon-Nitrogen Model 14. component, biogeochemical version the The Community specific model Land configura- forProgram Model version (CLM) the 2 with land (POP2) the for component, the the ocean Parallel component, Community Ocean Ice CodE (CICE) for simulation. Conclusions are presented in Sect. 5. 2 Models, methods, and data for this analysis. Sections 3 and 4 describe and analyze the data obtained from the 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 1 − ) yr 4 in atmospheric 1 − ) yr at steady-state in our 4 4 of CH 1 − mol mol 6 − , which is at the upper end of recent esti- 1 10 − 26484 26483 × ) yr 4 ect on our model to our clathrate emissions. ff ered only in the addition of 139 Tg(CH ff concentration and temperature (about 70 yr), the simulations for 4 We do not claim that this is the most likely scenario because there is still a lot of un- Methane is a long-lived gas, whose molecules reside in the atmosphere for about To study the climate impact of our methane release from Arctic clathrates, we ran two Not all of the methane leaving the sediment will make it to the atmosphere. Some Our simulation results showhave, the from potential impact the the scenario extra methane described emissions in could the previous section, on surface methane, including the extent to which methanethe atmosphere. may be However we destroyed do in consider theis this ocean also to before be it comparable a reaches plausible toing scenario. permafrost, plausible This scenario wetlands, scenarios rice, forapplication. fracking), other so methane many reservoirs of our (e.g. results decay- should have a broad 3 Response of annual mean quantities to clathrate emissions locations that corresponded towere in the the three Barents largest Sea,the Canadian predicted ratio Archipelago, 5 emission and : Sea 5 locations, : of which 1 Okhotsk (the in precise approximately locationscertainty are shown in in the Fig. magnitude 2). and location of possible methane releases from clathrates, mates (IPCC AR4: Solomonin et atmospheric al., CH 2007).the After Arctic the Emission control case run(hereafter (hereafter reached referred referred to steady as to state C). asso We the AE) discarded AE a branched simulation further from could 50 reachocean yr the a drift. of control new spin-up This equilibrium, run in left and both 449 werespectively. simulations saw and The no 420 extra yr impact of in methane any steady(a from deep state 22 the to % analyze Arctic increase for sediment the in model AE the and of global C 139 cases, total) Tg(CH was added to the control emission in 3 specific emissions for the controllated by simulation the to model was ensurean close that to average the the surface currently mixing methane observed ratiocontrol value. concentration of Specifically, run, we simu- 1.79 achieved whichkencky is et comparable al., to 2009), recent with observations 629 Tg(CH (Rigby et al., 2008; Dlugo- concentration for present-day atmosphere is known very accurately, we first scaled the known to an accuracy of about 15 % (IPCC AR4: Solomon et al., 2007) but the resultant mospheric chemistry described above. Thethe control present-day simulation distribution (C) used andsion an magnitude simulation estimate of of (AE) methane di methane emissions emissions. over The the Arctic Arctic andtwo Sea emis- simulations of provided Okhotsk. an Comparing estimate thethat output of is of analyzed the these in impact the of sections our below. clathrate emission scenario 9 yr on averagecause before the total they emission are and destruction destroyed rates (IPCC for methane AR4: in the Solomon present-day are et only al., 2007). Be- wetlands, rivers, East Siberian continental shelf, andwould thawing have permafrost a regions, very which similar e long climate simulations (about 539case) yr using for the the control fully and coupled 499 ocean-atmosphere-land yr CESM for model the with Arctic interactive emission at- will vent to the atmosphere moreuncertain, quickly. with Because ocean estimates and ranging sediment fromignore losses almost these are no very losses, loss i.e. to we almostatmosphere. assumed We total 100 did loss, % this we transmission because chose ofcertainty our to in methane primary sea-floor from goal emissions seafloor was is to large asion enough sensitivity may that be study, any and compensated error the for in un- emission by our a uncertainty assumed transmis- larger comes than from expected thein sea-floor fact the emission. that northern Part there high of are latitudes the also that other are sources sensitive of to methane warming, such as the northern lakes, previous studies have suggested thethe fraction surface of is methane only from aboutrecent clathrates 1 modeling % that (Lamarque, study reaches 2008; shows Elliottmight that et reach as the al., much atmosphere 2011a). (Elliott However, astrient a et 80–100 limited, more % al., or 2011b) of the if methane the ocean bubbles dissociated rise methane become higher nu- in the ocean from which the methane 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 4 increase. 2 erence of the ff erences at the poles could ff ects will be muted in the annual-mean, erence, but is slightly increased at the ff ff response are currently underway, but are not 2 26486 26485 erence between the AE and C simulations if the long-term ff erence in each gridcell by the standard error of the timeseries ff erence, standard deviation, and signal-to-noise (SNR) ratio at the ff erent from the standard CO ff erence in annually averaged surface temperature between AE and C in ff erence is greater in the polar regions compared to lower-latitudes. This raises ff The di The increase in surface methane concentration between the Arctic emission case the change is statistically significant almost everywhere. the question of whetherbe the the result larger of meanto chance. temperature A noise di basic ratio test (SNR)mean is of temperature to the di perform temperature ain increase, point-wise the z-test which same using is gridcell the (i.e. computednumber signal the by of temporal dividing time standard the deviation points,shows divided assuming that by the independence). square SNR This root atthough of SNR the the the is poles signal is is shown indeed greaterat in at generally lower Fig. latitudes, the less but 3d poles, than the because at and SNR of lower is the latitudes, still smaller generally even greater interannual than variability 3 over the poles, indicating is broadly similar topoles the because pattern of of thethe colder the temporal temperatures standard raw deviation in di of the theAE annually control simulation. averaged Just base temperature like state. di the controlature Figure simulation di 3c (not shows shown), the variability in the temper- extent, over land, with anear global mean the temperature poles increase where oferal the about pattern 0.2 temperature K, that increases and is by regions seenThe over in additional 0.5 K. response simulations This to necessary is radiativesponse to the forcing is determine di from same whether a gen- our uniformfar clathrate CO enough methane advanced re- at thetic time warming of is writing further to enhanced determine,the by for mean the example, percentage excess whether methane increase the in in Arc- the surface region. temperature Figure of 3b AE shows relative to C. The pattern dard deviation of themean of di the controlthe is C used, simulation. since there will be noFig. contribution 3a to shows the a variability definite from pattern of greater warming at high latitudes and, to a lesser deviation of the annual-mean methane concentration is entirely equivalent to the stan- than would be expected due to the increase in the mean alone. Note that the standard linear response is expectedradical due (OH) to in the the atmosphere factreducing the the that concentration main as of chemical OH loss methane(Prather, in of reacts methane the 1996). with and atmosphere However, thereby decreases, the increasing our hydroxyl temperature the simulation lifetime and of is water-vapor CH fully feedbacksthe as interactive, annual-mean methane so well. concentration The our inthe the temporal change AE scale standard includes scenario has deviation is been shown of chosencrease in to in Fig. reveal 2d, interannual features where variability inbut has regions as broadly other will than the the same be Arctic. pattern shown This as more in- the clearly mean in increase, section 4, the increase in variability is greater AE case withfeatures. respect These to results the showcentration control, about of a with methane 38 Fig. although % clearlyincreases increase 2c in there in using the are the Northern a regions global Hemisphere,ble with finer and mean the even the scale surface percentage higher Arctic increase con- percentage to in in particular. show the This methane more is emissions, almost which dou- was about 22 %. A non- (AE) and theeverywhere. control Because case of (C) thethe is smoothness high shown of values in the field nearscale Fig. over that the most 2a. clearly conveys of clathrate As the the distribution. emissionFig. expected, rest A 2e, of clearer locations, we which understanding the and shows see may planet, be thecant it increases gained zonal enhancement is from in mean hard the of to Northern the find Hemisphere,Figure data. in a 2b, It spite color c of can the shows be long-lifetime the seen of methane. percentage that there increase is in a surface signifi- methane concentration for the percentage di Earth’s surface for the annualtage means that of they each are variable. less Annualdepends noisy means on than have location. seasonal the However, means, any advan- and seasonalso the e seasonal timing impacts of will seasonal be impacts larger than indicated by our figures. temperature, ozone and precipitation, which we will present by examining the mean, 5 5 25 15 20 10 25 20 10 15 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | erence ff erences of 10 % ff ect. Overall then, ff erence in precipitation, ff concentration, which in turn erences between the tropical 4 ff erently by the clathrate emissions. ff 26488 26487 erence in surface ozone concentration shows ff erence in annually averaged ozone between AE ff ected di ff ect. In order to see the changes in variability over the rest of the planet, ff The changes in precipitation between the AE and C cases are shown in Fig. 5. But Next we show the changes in surface ozone concentration due to our Arctic clathrate emissions was a simpleof scaling methane of concentration the are concentration a field, i.e. the mean and variation variability ratios, with thein variability the in C the case,increase AE in especially case variability near must being whereplume be tens around, because the because of of the clathrate chemical times dynamical lifetime emissionsa variability greater of chemical were methane blowing than is e the introduced. too downwind long This the for it same to quantity be is primarily reproduced with1.5 a for finer most scale regions, in i.e. Fig. overthe 50 6b. variability % This increases. has plot When shows increased compared ratios by over to more Fig. than 2c, it it would is have clear if that the response to the clathrate model, we also seeparticularly the changes methane in and ozone thein concentrations. the interannual The AE ratio variability case of to of the thetemperature, standard corresponding some ozone, deviation standard of deviation and in the the precipitationdeviations control quantities, for case is methane for is methane, shown shown in in Fig. Fig. 6a. The 6. northern The high latitudes ratio show of very high the standard the CMIP3 intercomparison (IPCCincreased AR4: precipitation at Solomon high et latitudesBut al., and a a 2007) word more can complex of be patternrarely caution at greater seen, must lower than namely be latitudes. 3. added here because the absolute value of4 our SNR is Response of variability to clathrateIn emissions addition to the mean changes caused by the methane clathrate emissions in our precipitation in the AE casea relative pattern to of the increased Cis and case significant. decreased are Figure precipitation, shown 5c but in showswhich it the Fig. highlights isn’t standard 5a, immediately the deviation b. clear of They largethe what the show internal changes di seen interannual in variability the in mean. precipitation However, in compared the to SNR plot, Fig. 5d, the pattern seen in abundant water and , respectively. The raw and percentage increases in mean our other figures. We did this because blue and brown are commonly associated with This highlights one way that global(Fiore air et quality al., is inter-related 2012). with Figurein global 4c ozone climate concentration shows change that the leads temporalozone to standard concentration the deviation in signal of Fig. to the 4d, noiseare di ratio which clearly for shows the that statistically increase the significant,SNRs in mean around surface with changes 20 discussed SNRs over above equatorial of regions. over 100 overnote polluted that the regions color and schemeblue has and been decreased chosen precipitation to in indicate brown, the which increased precipitation is in the opposite color convention to extratropical ocean regions. It isand not extratropical clear whether oceans the are di our a Arctic dynamical, chemical clathrate or emissionwhich combined increases produces e the a global global increaseincreases methane of the emission 39 mean % by surface in about ozone surface 22 concentration CH %, by 10 % (and more in urban areas). Himalayan Plateau. The reasona for chemical this response, is sosuch unclear. it as We is increased see presumably downwellingthe no of the diagnostics evidence ozone response to from that ofin confirm the this some surface this stratosphere, is dynamical ozone but in change, concentrationin we our for Fig. do current the 4b. not AE simulations. Although have higher case the The values with percentage in percentage more di respect increase pollutedor to regions more the in as regions expected, control over there the is equatorial are oceans shown also that di are larger than the increases over the emissions. Figure 4a showsand the C. An di increaseurban in areas ozone with is already observed poorin everywhere, air the but quality. Urban presence is areas of particularlyet generate which more enhanced al., nitrogen in tropospheric 2008). oxides, methane Interestingly, we oxidizes and also produces see ozone an (Fiore increase in ozone concentration over the 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | n R . If n , (1) n 1 √ = ) ciently long time n 1 2 ffi + n 1 2 ( r = 2 ciently long time series that has   ) denotes the relative uncertainty n ffi R C C R 2 ∆ σ σ √   + for a su 2 >   2 26490 26489 n 2 denotes the expectation of the variance, and AE AE σ √ σ < s > 2   1) − n v u u u t 1 < s 2( = √ 2  C C σ σ ∆  + term in the above expression can be well approximated by 2 ) is given by  1 s − AE AE n σ ( σ ∆  s = Figure 6e shows the ratio of standard deviations for precipitation. As with tempera- In Fig. 6c we see the ratio of the standard deviations for surface temperature of AE Figure 6d shows the ratio of standard deviations for the surface concentration of Of course, it is necessary to know whether any change in the variability is statis- R R ∆ ulated will occurthe from uncertainties some of combination all of these these sources for sources, methane and emissions it to is get much possible larger, within with certainties in the estimatesthe of ocean. clathrate However, abundance, there releaserable are rate, to other and potential our consumption sources scenario, in ing), of including rice additional natural production, methane gas ruminant compa- lands, farming, production methane and by other trapped hydraulic natural below fracturingand Arctic relic (frack- sources permafrost such lakes. as (e.g. Recentis wet- the research a East (Wadham large et Siberian amountbe of al., Arctic vulnerable methane 2012) to Shelf), clathrates warming. also beneath Hence, suggests it the there is Antarctic likely ice that shelves a that scenario could similar to the one we sim- 5 Conclusion and discussion The previous sections presentedfor the release predicted consequences of of methane a from “what Arctic if” scenario clathrates that is plausible, considering the un- which is not surprising givenis that sensitive the to methane methane variability concentrations. increased and ozone creation ture, we see that theare changes mostly in within variability includenificant the both change 2-sigma increases is and range. decreases thetongue The that decrease region only in in region the precipitationmean that eastern variability drying. tropical might in Pacific, be the which showing model’s is El a about 2-sigma Nino sig- greater dry than the sideration of the increaseare in many the regions mean, that Fig.regions are 4b, that not and are significant the significant. at uncertainty Itvariability the than in is 2-sigma the also the level, increase noteworthy in ratio, but that thestatistically there there mean significant. nearly are would Hence, all still suggest, it locations even many would if show appear they greater that are the not ozone individually variability does increase, Hemisphere oceans, although there is an increase over most of the planet. After con- ozone. Perhaps surprisingly, the increase in variabilityily in greatest surface in ozone is polluted not regions. necessar- The variability seems to increase most in the Southern is the number ofseries, independent the time points (Squires,denotes 1991). the For ratio of a two su in standard it, deviations, then and can ( be derivedthe from usual the rules uncertainty for in calculating the the individual standard uncertainty deviations in using a ratio: Thus, we see that thein uncertainty in our the time ratio is series.the dependent Hence, ratio only on of with the the time-series number standardthe of of deviations years increase of over in AE 400 methane yr tovariability variability, C the is we turns over now 1-sigma 3-sigma out see uncertainty greater to that than in be in the about most increase 5 in %. locations thecompared Returning the mean to to increase alone in C. would imply. Weso see most locations increases are and notchanges decreases significant in at of variability, the but up with 2-sigma so to level.a many There 10 few locations are %, it places regions or is with that always so, larger significant exceed expected in change that a there in variability, 2-sigma will variability change, be for so temperature. it is hard to say whether there is any tically significant. Weusing can standard estimate statistical error the analysis asdard uncertainty follows. deviation The in estimated uncertainty each in a standard stan- deviationa ratio Gaussian distribution, where 5 5 25 15 20 10 25 10 15 20 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | , 2007. , 2004. C in conjunction with ce of Science of the US ◦ ffi concentration equivalent to our 10.1016/j.epsl.2004.09.005 2 10.1088/1748-9326/2/4/045015 26492 26491 , 2007. erent methane sources. For reference, a model study ff , 2009. , 2011. This work was sponsored by the US Department of Energy (BER), per- ett, B., and Brovkin, V.: Ocean methane hydrates as a slow tip- ff 10.5194/bg-4-521-2007 10.1029/2011gl047222 10.1073/pnas.0800885105 ett, B. and Archer, D.: Global inventory of methane clathrate: sensitivity to changes in the ff Casanova, S. E.har, B., L. Dufresne, J. K.,Tsushima, L., Ingram, Y., Fillmore, Uchiyama, W. D.house J., T., W., gases: Forster, and Kratz, estimates P. Zhong, D. M. from W. D., P., climate Galin, Lefebvre, Y.: models Radiative V. M. in Y., forcing the P., Go- by Li, Intergovernmental Panel well-mixed J., on green- Marquet, Climate P., Oinas, V., system model: atmospheric chemistry, coupling,Scientific and Discovery petascale through computing, Advanced Computing, in: 2006. Scidac 2006: Latif, M., Boening, C.cause W., gas Madec, hydrate G., destabilization and anddoi: Wallmann, ocean K.: acidification, Rising Geophys. Res. Arctic Lett., Ocean 38, temperatures L08602, Friborg, T.: Methane emissions from western Siberianto wetlands: climate heterogeneity change, and Environ. Res. sensitivity Lett., 2, 045015, doi: deep ocean, Earth Planet. Sci. Lett., 227, 185–199, doi: ping pointdoi: in the global , P. Natl. Acad. Sci. USA, 106, 20596–20601, 521–544, doi: Additional simulations with a globally uniform CO In order to study the potential reinforcement between the methane sources sus- Of the changes between our simulations with and without Arctic clathrate emissions, Collins, W. D., Ramaswamy, V., Schwarzkopf, M. D., Sun, Y., Portmann, R. W., Fu, Q., Cameron-Smith, P., Lamarque, J. F., Connell, P., Chuang, C., and Vitt, F.: Toward an Earth Biastoch, A., Treude, T., Ruepke, L. H., Riebesell, U., Roth, C.,Bohn, Burwicz, T. E. J., Lettenmaier, B., D. P., Park, Sathulur, K., W., Bowling, L. C., Podest, E., McDonald, K. C., and Bu Archer, D., Bu understood about the impact of Arctic methaneAcknowledgement. emissions on the Earth system. Archer, D.: Methane hydrate stability and anthropogenic , Biogeosciences, 4, sea-ice and the stratosphere also remain to be examined, so there is stillformed much under to the be auspicesLaboratory of under the Contract US DE-AC52-07NA27344, Department andResearch of used Scientific Energy resources Computing by of Center, LawrenceDepartment which the Livermore of National is National Energy Energy supported under by Contract the No. O DE-AC02-05CH11231. References plification factors between the di (Bohn et al., 2007)a found 10 that % increase an in increaseto precipitation of doubling in of temperature the annual by Western methane 3 Siberian emissions. region of wetlandsmethane could lead clathrate forcinghancements will we allow see in us temperatureemissions to and are precipitation determine quantitatively with enhanced our whether, above Arctic thegreenhouse or clathrate usual gas methane response not, forcing simulated the for by uniform Arctic the non-uniform en- methane concentration. 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M., Maltrud, M., and Cameron-Smith, P.: Basin-scale ass- 5 5 15 10 25 30 10 20 15 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | the show (b) (a) the zonal mean (e) C per century at 400–600 m, ◦ 3 + the same percentage increase but (c) (b) (d) (b) 26498 26497 from C to AE (ppmv). The arrows in panel the Sea of Okhotsk. Note that the red lines show the 4 (b) C per century at 350 m, ◦ 5 + (e) . This particular scenario assumed ocean bottom temperatures 1 outgassing from clathrates as a function of depth and time inte- − 4 the mean increase (ppmv) of the AE case over the C case, ) yr 4 (a) the standard deviation of the AE case (ppmv), and (d) the Arctic Ocean and (a) (c) (a) C per century below 600 m, with no further change after the first century. ◦ The change in methane concentration at the surface between the Arctic emission and Simulated flux of CH 1 + (a) the location of the clathrate emissions in our model. percentage increase of thewith AE a case finer over scale, increase the in C surface case, concentration of CH the control simulations: Fig. 2. Fig. 1. grated over and flux for particular depth ranges,sions and have the units blue of Tg(CH linesthat show followed the a sum linear of increase all of the red lines. The emis- Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | (d) the (b) the percentage (b) the standard deviation of the AE case (c) (d) (b) (d) (b) the standard deviation of the AE case (K), and 26500 26499 (c) the mean increase (ppbv) of the AE case over the C case, (a) the mean increase (K) of the AE case over the C case, (a) the signal to noise ratio of the mean increase. (d) The change in ozone concentration at the surface between the Arctic emission and The change in skin temperature at the surface between the Arctic emission and the con- (c) (a) (c) (a) percentage increase of the AE(ppbv), case and over the C case, Fig. 4. the control simulations: increase of the AE case over the C case, Fig. 3. trol simulations: the signal to noise ratio of the mean increase. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | the per- the surface (b) (e) the standard deviation of the AE case (c) (d) (b) (d) (b) the surface methane concentration at a finer ) of the AE case over the C case, 1 − (b) 26502 26501 the surface ozone concentration, and (d) (e) the signal to noise ratio of the mean increase. (d) the mean increase (mmday (a) ), and (a) (c) the surface skin temperature, 1 − The ratio of the standard deviations of the Arctic emission case over the control case The change in precipitation at the surface between the Arctic emission and the control the surface methane concentration, (c) (a) (c) (a) precipitation. Fig. 6. for scale, centage increase of the(mmday AE case over the C case, Fig. 5. simulations: