微观经济学外部性的讲解

过度捕捞的外部性过度捕捞存在外部性原因2.外部性在过度捕捞中发挥的作用Anexternalityreferstotheuncompensatedimpactofoneperson’sactionsonthewell-beingofabystander.Externalitiescausemarketstobeinefficient,andthusfailtomaximizetotalsurplus. ...whenapersonengagesinanactivitythatinfluencesthewell-beingofabystanderandyetneitherpaysnorreceivesanycompensationforthateffect.…当一个人的行为影响到旁观者的福利时，若此人既不为此支付成本（给旁观者带来成本时）又不能得到补偿（给旁观者带来利益时），外部性就产生了。Whytheexternalitiesoccur?1.Themostfundamentalreasonisthatresourcesarescarce.2.Becausefishofpublicpondsarecompetitiveandnon-exclusivecommonresources.Itmeansthatapersoncatchesmorefish,leavingotherpeoplelessfishtocatch.What'smore,thepondispublic,fisharenotexclusiveitems,andeveryonecangofishing.So,whenthepondstherearepublicresources,theymaycausetheoverfishing.Thisisagoodnewsforthoseself-interestindividualschasingeachinterestmaximization,butmaycauseharmontheoverall.Profitmaximizingfishingtendstooverfishingandwilldestroylivingsofthecommercialvalueinthepond.3.Andatoolargerangeofresourcesislikelytoleadtothisphenomenon.Overfishingintheinternationalseasisoneexample,leadstoasignificantreductioninfisheriesresourcesandeventothebrinkofextinction.Howtodealwiththis？中国政府的解决之路1.为防止过度捕鱼，中国政府要求，2009年5月16日至8月1日期间禁止在我国南海的部分区域捕鱼，并派出渔政船形成编队巡航2.敦促管理者制定更严格的环境保护规定3.中国政府发放捕鱼证来保证捕鱼量政府税收（tax）

管制（governmentforce）

捕鱼证（marketpower）

道德规范，协议合同（CoaseTheorem）PigoviantaxesInternalizinganexternalityinvolvesalteringincentivessothatpeopletakeintoaccounttheexternaleffectsoftheiractions.外部性的内在化——通过增加成本，使人们考虑他们自己过度捕鱼行为的不良效应。Thegovernmentcaninternalizeanexternalitybyimposingataxontheproducertoreducetheequilibriumquantitytothesociallydesirablequantity.政府可以向生产者收税以降低市场均衡产量为社会所希望的产量，将外部性内在化。Indirecttaxation可以被转移的间接税sellerscansellinahigherprice（Directtaxation针对个人收入等

直接税）科斯定理

TheCoaseTheoremisapropositionthatifprivatepartiescanbargainwithoutcostovertheallocationofresources,theycansolvetheproblemofexternalitiesontheirown.

TypesofPrivateSolutionstoExternalities

Moralcodesandsocialsanctions

道德规范和社会约束Charitableorganizations

慈善组织Integratingdifferenttypesofbusinesses

不同类型的企业一体化Contractingbetweenparties

交易各方签订合同Themarketistoocruel（完全竞争市场）Tradablepollutionpermits

allowthe

voluntarytransferoftherighttocatchfishfromonefirmtoanother.

Amarketforthesepermitswilleventuallydevelop.Afirmthatcanreduceoutputatalowcostmayprefertosellitspermittoafirmthatcanreduceoutputonlyatahighcost可交易的捕鱼证允许捕鱼权交易这种许可证的市场将最终形成。以低成本可以捕鱼的企业愿意将证出卖给只有以高成本才能捕鱼的企业。捕鱼量没有增加，但捕鱼证这一稀缺资源重新配置给对其评价更高的企业。NobodyisgoingtoobeyThemarketiscruel，lowcostforenteringTax