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Global Change

by: Joy Braun

Global Change ENVE 118

Joy Braun
GPA 3.95

Anthony Westerling

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Anthony Westerling
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This 2 page Class Notes was uploaded by Joy Braun on Thursday October 29, 2015. The Class Notes belongs to ENVE 118 at University of California - Merced taught by Anthony Westerling in Fall. Since its upload, it has received 28 views. For similar materials see /class/231719/enve-118-university-of-california-merced in Environmental at University of California - Merced.

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Date Created: 10/29/15
overcome the unfavorable reaction to form a microtubule but soon a er formation the mi crotubule is liberated It will be of considerable interest to determine the molecular composi tion of the nucleating sites in Ambidopsis and the mechanism of microtubule release The new observations of microtubule be havior inplant cells which lack a conventional centrosome are remarkably similar to previous plasts contain fewer and more disorganized microtubules than the parental cells from which they were derived In cytoplasts pre pared from fibroblasts microtubules with two free ends are observed and these microtubules treadmill 10 Both in the plant cortex and the cytoplast the apparent motion of the micro tubule results from gain and loss of subunits at opposite ends the lattice of the microtubule is stationary presumably because of linkage to other elements of the cytoskeleton see the fig ure B Interestingly microtubule behavior in cytoplasts is cell type wecficmicrombules in cytoplasts derived from epithelial cells have a static minus end and a plus end that shows dynamic instability 10 Minusend capping complexes are likely to regulate microtubule behavior in these cells see the figure B In contrast to the tethered microtubules ob served in the plant cortex animal cells use mo tordriven microtubule transport to establish and maintain noncentrosomal microtubule ar rays in diverse cell types see the figure B and to rearrange the microtubule array during cell locomotion I I 12 This behavior is par ticularly striking in nerve axons where micro tubules are transported long distances by rapid but highly infrequent episodes of motility I I In this case the behavior is more like the proverbial hare with bursts of activity fol lowed by stasis or even reversal The absence of cytoplasmic dynein from the Ambidopsis genome may partially explain the lack of mi crotubule transport as well as the inability of microtubules in higher plant cells to organize their minus ends into tightly focused arrays Although the plus end of the microtubule has been the focus of much study it is clear that a complete understanding of microtubule be havior will require an appreciation of what hap pens at the minus end as well It will be partic ularly important to determine the mechanism by which microtubules are nucleated in vivo and to learn which aspects of this process are conserved in diverse cells Abetter understand PERSPECTIVES ing of microtubule nucleation may also shed light on the mechanism of release and on how cells regulate its frequency For example recent observations of motile fibroblasts have shown that microtubule release from the centrosome is more frequent than previously estimated and that this release contributes to cell motility 13 Clearly much remains to be learned about how plant and animal cells generate microtubule ar rays with distinct dynamic properties by regu lating microtubule nucleation release and dy namic turnover References and Notes R L Margolis L Wilson Bioessays 20 830 1998 TJ Mitchison MW irsc ner Nature 312237 1984 C MWatermaantorer etaL Curr Biol 7 R369 1997 J M Hush etal j Cell Sci 107 775 1994 M Saxton eta j Cell Biol 99 2175 1984 S L Shaw etaL Science 300 1715 2003 published online 24April 2003 101126science1083529 In tobacco Y2 cells microtu ule s ortening rates simr ilar to mose in animal cells were recently reported Y A Komarwa etalj Cell Sci 115 3527 2002 T J Keatng er al Proc Nat Acad Sci USA 94 5078 1997 V Rodionov etaL Proc Natl Acad Sci USA96 115 1999 mSi FWZVr 1 Logo 0 LWang A Brown Curr Biol 12 1496 200 A SW rm CellBiol15110032000 M Abal etal j Cell Biol 159 731 2002 P DhonuksheTW J Gadella PlantCell15 597 2003 15 I thank P K Hepler for helpful comments Mw CLIMATE CHANGE A Guide to C02 Sequestration Klaus S Lackner limate change concerns may soon Cforce drastic reductions in C02 emissions In response to this chal lenge it may prove necessary to render fos sil fuels environmentally acceptable by capturing and sequestering COZ until other inexpensive clean and plentiful technolo gies are available Today s fossil fuel resources exceed 5000 gigatons of carbon GtC 1 com pared with world consumption of GtCyear assuring ample transition time However by 2050 the goal of stabilizing the atmospheric COZ concentration while maintaining healthy economic growth may require carbonneutral energy in excess of today s total energy consumption 2 Lowering world COZ emissions to 2 GtCyear would shrink the per capita emis sion allowance of a projected world popu lation of 10 billion people to 3 of today s per capita emission in the United States If sequestration is to achieve this goal it must operate on a multiterawatt scale while sequestering almost all produced C02 It The author is in the Department of Earth and Environmental Engineering Columbia University New York NY 10027 USA Email kl2010columbiaedu www5ciencemagorg SCIENCE VOL300 must also be safe environmentally accept able and stable For small stored quantities storage time requirements can be minimal 3 But as storage space fills up lifetime constraints due to aggregate leakage emis sions would tighten until storage times for the entire carbon stock would reach tens of thousands of years If carbon emissions are reduced mainly through sequestration then total carbon storage in the 21st century will likely exceed 600 GtC Because leaking just 2 GtCyear could force future generations into carbon restriction or recapture pro grams even initial storage times should be measured in centuries Storage time and capacity constraints ren der many sequestration methodsgsuch as biomass sequestration and C02 utilizationi irrelevant or marginal for balancing the car bon budget of the 21st century Even the ocean s capacity for absorbing carbonic acid is limited relative to fossil carbon resources 4 Moreover with natural ocean turnover times of centuries storage times are compar atively short Generally sequestration in en vironmentally active carbon pools such as the oceans seems ill advised because it may trade one environmental problem for another Underground injection is probably the easiest route to sequestration It is a proven technology suitable for largescale seques tration 3 Injecting COZ into reservoirs in which it displaces and mobilizes oil or gas could create economic gains that partly off set sequestration costs In Texas this ap proach already consumes 20 million tonsyear ofCOZ at aprice of10 to 15 per ton of C02 However this is not sequestra tion because most of the C02 is extracted from underground wells il and gas sites have limited capacity see the figure Once they fill up saline aquifers may be used as demonstrated un der the North Sea where the Norwegian energy company Statoil has sequestered COZ removed from natural gas 6 7 Ubiquitous saline reservoirs imply huge storage capacities However because of un certainties in storage lifetimes seismic in stability and potential migration of buoyant COZ longterm integrity must be estab lished for each site more expensive but safer and more permanent method of C02 disposal is the neutralization of carbonic acid to form car bonates or bicarbonates 4 Neutralization rmodynamically favored and results in stable products that are common in na ture Mineral deposits larger than fossil re sources ensure essentially unlimited sup plies of base ions mainly magnesium and calcium but also sodium and potassium 13 jUNE 2003 Downloaded from wwwsciencemagorg on March 14 2009 1 677 1 678 PERSPECTIVES The least expensive way to neutralize COZ may be its injection into alkaline mineral strata COZ would gradually dis solve into the pore water Because it is acidic it would leach mineral base from the rock resulting in carbonates or bicarbon ates that eliminate all con cerns over longterm leakage Neutralizing car bonic acid with carbon ates as a base would cre ate aqueous bicarbonate solutions Unless injected underground they would likely find their way into the ocean which fortu nately could accept far arger amounts of bicar bonates than of carbonic acid A better option than forming watersoluble bi 9n I o e I 3 I Characteristic storage time years 3m o I 5quot ie 5 gr 0 1 o H a m 2 E a stored at the location of the mineral base confin ing environmental impact to a specific site To this end serpentine or olivine rocks rich in magnesium silicates can be mined crushed milled and reacted with C02 Estimated mining and mineral prepara tion costs of less than 10 per ton of C02 seem acceptable adding 05 to 1 to a kilo watthour of electrici Improved methods for accelerating car bonation are however still needed The cur rent best approachgcarbonation of heat treated peridotite or serpentine in an aque ous reactioniis too costly Elimination of the energyintensive heat treatment could render the process economically and ener getically feasible Aboveground mineral se questration has the capacity of binding all COZ that could ever be generated and limit ing the environmental impact including ter rain changes to relatively confined areas Most sequestration methods require concentrated COZ which is best captured at large plants that generate clean carbon free energy carriers such as electricity and hydrogen Retrofitting existing plants ap pears too expensive new plants designed for COZ capture are more promising 8 Complete COZ capture opens the door to radically new power plant designs that eliminate all flue gas emissions not only COZ Oxygenblown gasification could approach this goal today More advanced designs could even remove the efficien consumption forthe tion held constant to 2400 Gt Ocean acidicquot and ocean neutralquot are the ocean39s uptake capacities for carbonic acid and neutralized carbonic acid respectivelyThe upper limits of capacity or lifetime for underground injec tion and mineral carbonates are not well constrained EOR stands for en hanced oil recovery a3 we or 7 Cu r4 0 ll 88 1 8 i no 7 353 Mineral Em n carbonates 00 5amp8 lt1 w Fossil cal bori OAVCIeHlllllll underground ection Ocean in nover infrastructure lifetime ya I I I 00 100000 1000000 I 100 1000 10 0 Carbon storage capacity Gt Estimated storage capacities and times for various sequestration methods The fossil carbonquot range includes at its upper end methane hy drates from the ocean floor The oxygen limitquot is the amount of fossil car v Iable in airfor 39 b Farhnn 21st century ranges from 600 Ct current consump cy penalty associated with C02 capture or le sending gasification prod ucts of coal together with steam through a uidized bed of lime would shi oxygen from water to carbon Capture of C02 on lime would promote hydrogen production and provide necessary heat Half of the hy drogenrich output would be used to gasify coal the other half would be oxidized in a hightemperature solidoxide fuel cell The waterrich spent fuel gas would be returned to the lime bed to repeat the cycle Only ex cess water ash and impurities captured in various cleanup steps would leave the plant Once the lime becomes fully carbonated limestone COZ would be produced in a con centrated stream while the limestone is con verted back to lime with waste heat from the fuel cell Careful heat management could drive power plant efficiency to 70 9 for comparison conventional coalfired power plants are in the 30 to 35 range modern gasfired power plants can approach 50 C02 is three times as heavy as fuel and therefore carmot be stored in cars or air planes COZ from these sources will have to be released into the atmosphere and recap tured later Currently photosynthesis is the only practical form of air capture Capture from air owing over chemical sorbentsi such as strong alkali solutions or activated carbon substratesiappears feasible but needs to be demonstrated 10 Wind is an efficient carrier of C02 The size of less than 1 that of capture apparatus would be windmills that displace equal COZ emissions suggesting that they could be quite cheap to build 11 The additional cost of sorbent recycling should also be af fordable 12 Because the atmosphere mixes rapidly extraction at any site however remote could compensate for emissions from any where else By decoupling power genera tion from sequestration air capture would allow the existing fossil fuelibased energy infrastructure to live out its useful life it would open remote disposal sites and even allow for the eventual reduction of atmos pheric COZ concentration Cost predictions for sequestration are un certain but 30 per ton of C02 equivalent to 13 per barrel of oil or 25 per gallon of gas appears achievable in the long term Initially niche markets for example in en hanced oil recovery would keep disposal costs low with capture at retrofitted power plants dominating costs Over time new power plant designs could reduce capture costs but the costs of disposal would rise as cheap sites fill up and demands on perma nence and safety tighten Some applica tionsifor example in vehicles and air planesicould accommodate the higher price of C02 capture from air eliminating COZ transport and opening up remote dis posal sites Today s urgent need for substantive COZ emission reductions could be satisfied more cheaply by available sequestration technolo gy than by an immediate transition to nu clear wind or solar energy Further develop ment of sequestration would assure plenti ful lowcost energy for the century giving better alternatives ample time to mature References and Notes 1 H7H Rogner Annu Rev EnergyEnw39ron 22171997 2 M Hoffert et al Science 298 981 2002 3 The reason is that eakage rates are proporu39onal to store age size and inversely proportional to storage lifetime K S LacknerAnnu ev nergy Environ S HollowayAnnu Rev Energy nviron rzog B Eliasson O Kaarstad Sci Am February mine 33 25 mo Q 88 3quot 72 dlt et at paper presented at me Sixth Intemau39onal Conference on Greenhouse Gas Technology CIHCITVB Kyoto Japan I to 4 October 2002 8 H J Herzog E M Drake Annu Rev Energy Environ 21 145 1996 9 T M Yegulalp K S Ladltner H7J Ziork int 1 Surf Mining Reclam Environ 15 52 2001 10 K S Lackner H7J Ziock P Crimes in Proceedings of the 24th international Conference on Coal Utilization estad Ed Coal Technology Associau on Clearwater FL 1999 pp 885396 1 At a wind spee o S er capita emission of 22 tonsyear ofCO2 ows through an opening of02 m Through me same opening blow 21 W ofwind power or 02 of the US per ca 39 39 39 12 F eman paper presented at the 2nd Annual Conference on Carbon SequestrationAlexandriaVA 5 to 8 May 2003 13JUNE 2003 VOL 300 SCIENCE wwwsciencemagorg Downloaded from wwwsciencemagorg on March 14 2009


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