learning and control in a changing economic environment abstract in this paper we investigate optimal bayesian learning and control with lagged dependent variables and time varying unknown parameters we assess both the performance of alternative decision rules as in the computationally oriented dual control literature as well as the dynamics of learning and convergence of beliefs as in the more theoretically oriented bayesian learning literature our numerical results indicate that the optimal decision rule involves a noticeable degree of experimentation for moderate to large levels of uncertainty in most situations though the optimal rule will remain less activist than a certainty equivalent rule and induce gradualism exceptions occur when the process to be controlled is near the deterministic steady state in this situation we find that the decision maker will repeatedly undertake costly experiments the extent of optimal experimentation is lower if the unknown parameter is perceived to vary over time in contrast to the fixed parameter case however parameter uncertainty is continually renewed and the incentive to experiment never ceases

active learning and optimal climate policy this paper develops a climate economy model with uncertainty irreversibility and active learning whereas previous papers assume learning from one observation per period or experiment with control variables to gain additional information this paper considers active learning from investment in monitoring specifically in improved observations of the global mean temperature we find that the decision maker invests a significant amount of money in climate research far more than the current level in order to increase the rate of learning about climate change this helps the decision maker make improved decisions the level of uncertainty decreases more rapidly in the active learning model than in the passive learning model with only temperature observations as the uncertainty about climate change is smaller active learning reduces the optimal carbon tax the greater the risk the larger is the effect of learning the method proposed here is applicable to any dynamic control problem where the quality of monitoring is a choice variable for instance the precision at which we observe gdp unemployment or the quality of education

survey measures of risk aversion and prudence this paper utilizes a thought experiment conducted by the bank of italy to estimate absolute and relative risk aversion along with absolute and relative prudence for a broad cross section of italian households upper and lower bounds are calculated for each parameter and comparisons are made across socio demographic groups evidence is found of decreasing absolute risk aversion decreasing absolute prudence increasing relative risk aversion and increasing relative prudence

are contributions to public pension programmes a tax on employment many studies describe the potentially adverse impact on employment of the payroll costs of financing public pension programmes conventionally empirical studies treat contributions to public pension programmes as a pure tax in for example calculations of the tax wedge by oecd but this approach ignores any future rights to benefits that are perceived by contributors in fact public pension programmes contain both an actuarial and a redistributive component the former closer to saving the latter a tax the paper constructs indicators of the tax component of pension programmes both between and within generations across a range of oecd countries and time periods it uses these measures in a cross country panel analysis of the determinants of age and gender specific economic activity rates the results reveal robust evidence that when public pension programme contributions are broken down into a tax component and a savings component the tax component of the payroll contribution reduces economic activity rates among women while a higher retirement saving component has the opposite effect there is little evidence that average tax rates however constructed have any adverse impact on the economic activity rates of men richard disney

global warming irreversibility and learning a number of economists have argued that the literature on the irreversibility effect implies that current abatement of greenhouse gas emissions should be greater when there is the possibility of obtaining better information in the future about the potential damages from global warming than when there is no possibility of obtaining better information in this paper we show that even the simplest model of global warming does not satisfy either of epstein s 1980 sufficient conditions so it is not possible to use epstein s analysis to tell whether the irreversibility effect applies to models of global warming we derive an alternative sufficient condition for the irreversibility effect to hold

on welfare frameworks and catastrophic climate risks recent theoretical work in the economics of climate change has suggested that climate policy is highly sensitive to fat tailed risks of catastrophic outcomes weitzman 2009 68 such risks are suggested to be an inevitable consequence of scientific uncertainty about the effects of increased greenhouse gas concentrations on climate criticisms of this controversial result fall into three categories the first suggests that it may be irrelevant to cost benefit analysis of climate policy the second challenges the fat tails assumption and the third questions the behavior of the utility function assumed in the result this paper analyses these critiques and suggests that those in the first two categories have formal validity but that they apply only to the restricted setup of the original result which may be extended to address their concerns they are thus ultimately unconvincing critiques in the third category are shown to be robust however they open up new ethical and empirical challenges for climate economics that have thus far been neglected how should we value catastrophes as a society i demonstrate that applying results from social choice to this problem can lead to counterintuitive results in which society values catastrophes as infinitely bad even though each individual s utility function is bounded finally i suggest that the welfare functions traditionally used in climate economics are ill equipped to deal with climate catastrophes in which population size changes drawing on recent work in population ethics i propose an alternative welfare framework with normatively desirable properties which has the effect of dampening the contribution of catastrophes to welfare

optimal learning on climate change why climate skeptics should reduce emissions climate skeptics typically argue that the possibility that global warming is exogenous implies that we should not take additional action towards reducing emissions until we know what drives warming this paper however shows that even climate skeptics have an incentive to reduce emissions such a directional change generates information on the causes of global warming since the optimal policy depends upon these causes they are valuable to know although increasing emissions would also generate information that option is inferior due its irreversibility we show that optimality can even imply that climate skeptics should actually argue for lower emissions than believers

pareto improving social security reform when financial markets are incomplete this paper studies an overlapping generations model with stochastic production and incomplete markets to assess whether the introduction of an unfunded social security system leads to a pareto improvement when returns to capital and wages are imperfectly correlated a system that endows retired households with claims to labor income enhances the sharing of aggregate risk between generations our quantitative analysis shows that abstracting from the capital crowding out effect the introduction of social security represents a pareto improving reform even when the economy is dynamically efficient however the severity of the crowding out effect in general equilibrium tends to overturn these gains

funded pensions and intergenerational and international risk sharing in general equilibrium we explore intergenerational and international risk sharing in a general equilibrium multiple country model with two tier pensions systems the exact design of the pension system is key for the way in which risks are shared over generations the laissez faire market solution fails to provide an optimal allocation because the young cannot share in the financial risks however the existence of wage indexed bonds combined with a pension system with a fully funded second tier that pays defined wage indexed benefits can reproduce the first best if wage indexed bonds are not available mimicking the first best is not possible except under special circumstances we also explore whether national pension funds want to deviate from the first best by increasing domestic equity holdings with wage indexed bonds this incentive is absent while there is indeed such an incentive when wage indexed bonds do not exist

climate change and optimal energy technology r d policy public policy response to global climate change presents a classic problem of decision making under uncertainty theoretical work has shown that explicitly accounting for uncertainty and learning in climate change can have a large impact on optimal policy especially technology policy however theory also shows that the specific impacts of uncertainty are ambiguous in this paper we provide a framework that combines economics and decision analysis to implement probabilistic data on energy technology research and development r d policy in response to global climate change we find that given a budget constraint the composition of the optimal r d portfolio is highly diversified and robust to risk in climate damages the overall optimal investment into technical change however does depend in a non monotonic way on the risk in climate damages finally we show that in order to properly value r d abatement must be included as a recourse decision

fundamental irreversibilities in stock externalities abstract this paper concerns the irreversibility effect in stock externalities in an environment of uncertainty with learning taking place one may wish to under emit today to avoid potential environmental irreversibilities alternatively one may wish to under invest in pollution control capital avoiding investments in sunk capital that turn out to be wasted the paper develops theoretical results on the tension between these two effects and separates risk aversion from the irreversibility effect the paper also presents a simple example in climate change policy

intergenerational risk sharing and risk taking of a pension fund abstract by using their financial reserves efficiently pension funds can smooth shocks on their asset returns and can thus facilitate intergenerational risk sharing in addition to the primary benefit of improved time diversification this form of risk allocation affords the additional benefit of allowing these funds to take better advantage of the equity premium which also favors the consumers in this paper our aim is twofold first we characterize the socially efficient policy rules of a collective pension plan in terms of portfolio management capital payments to retirees and dividend payments to shareholders we examine both the first best rules and the second best rules where in the latter case the fund is constrained by a solvency constraint and by a guaranteed minimum return to workers contributions second we measure the social surplus of the system compared to a situation in which each generation would save and invest in isolation for its own retirement we estimate that the certainty equivalent return of the pension saving scheme goes from 3 23 per year to 3 76 when intergenerational risk sharing is introduced one of the main results of the paper is that better intergenerational risk sharing does not reduce the risk born by each generation rather it increases the expected return to the workers contributions

regulation with anticipated learning about environmental damages a regulator anticipates learning about the relation between environmental stocks and economic damages for a model with linear quadratic abatement costs and environmental damages and a general learning process we show analytically that anticipated learning decreases the optimal level of abatement at a given information set if learning causes the regulator to eventually decide that damages are higher than previously thought learning eventually increases abatement learning also favors the use of taxes rather than quotas using a model that is calibrated to describe the problem of global warming we show numerically that anticipated learning causes a significant reduction in first period abatement and a small increase in the preference for taxes rather than quotas even if the regulator s initial priors about environmental damages are much too optimistic he is able to learn quickly enough to keep the expected stock trajectory near the optimal trajectory

designing social security a portfolio choice approach public social security systems may provide diversification of risks to individuals life time income capturing that a pay as you go program paygo may be considered as a quasiasset we study the optimal size of the social security program as well as the optimal split between a funded part and a paygo part by means of a theoretical portfolio choice approach a low yielding paygo system can benefit individuals if it contributes to hedge other risks to their lifetime resources moreover a funded part of the social security system can be justified by potential imperfections to the individuals free access to the stock market numerical calculations for sweden norway the us and the uk demonstrate that the optimal size of paygo part of the pension program varies considerably in response to differences in projected growth rates and the correlation between stock returns and growth our calculations suggest that a paygo program has an important role in the three former countries but not in the u k

stochastic control for economic models past present and the paths ahead abstract on the 30th anniversary of a meeting between engineers and economists at princeton university to discuss the potential application of stochastic control methods to economics this paper provides a review of past present and paths ahead the events surrounding some of the key developments of the past are described along with a discussion of the present state of the research and of paths for future research the paper is structured around the primary methods for solving quadratic linear economic stochastic control models namely open loop classical control handcrafted feedback rules optimal feedback min max control optimal feedback rules with parameter uncertainty and dual control the paper also includes a discussion of software developments in economic stochastic control modeling

intergenerational risk sharing abstract in this paper we examine government debt and tax transfer policies that can be improve the allocation of risk between generations markets cannot allocate risk efficiently between two generations whenever the two generations are not both alive prior to the occurence of a stochastic event this implies that government policies transferring risk between generations have the potential to create first order welfare improvements our model provides a non keynesian justification for the debt finance of wars and recessions as well as an added rationale for social security type tax transfer schemes which aid unlucky generations e g the depression generation at the expense of luckier generations

caution and probing in a macroeconomic model abstract this paper reports on the application of an adaptive dual control technique to a small macroeconometric model of the u s economy both monetary and fiscal policy variables are used in the model the experiments find that probing and active learning will occur in small macroeconometric models but that unrealistically high terminal period penalties on state deviations are required before it appears

learning experimentation and monetary policy abstract we present a model of monetary policy where the policymaker faces uncertainty about which he is learning in a bayesian fashion a fixed money supply rule is not optimal since the learning leads to adjustments in the monetary action we present cases in which it is optimal to bear some cost in terms of current output performance in order to gain information that can be used in the formulation of future monetary policy experimentation therefore pays we also show that even passive learning without experimentation still leads to an activist monetary policy i e one that is responsive to new information

climate policy under fat tailed risk an application of dice uncertainty plays a significant role in evaluating climate policy and fat tailed uncertainty may dominate policy advice should we make our utmost effort to prevent the arbitrarily large impacts of climate change under deep uncertainty in order to answer to this question we propose a new way of investigating the impact of fat tailed uncertainty on optimal climate policy the curvature of the optimal carbon tax against the uncertainty we find that the optimal carbon tax increases as the uncertainty about climate sensitivity increases but it does not accelerate as implied by weitzman s dismal theorem we find the same result in a wide variety of sensitivity analyses these results emphasize the importance of balancing the costs of climate change against its benefits also under deep uncertainty 2013 springer science business media dordrecht

learning and stock effects in environmental regulation the case of greenhouse gas emissions abstract this paper concerns the optimal regulation of greenhouse gases that lead to global climate change in particular we focus on uncertainty and learning which over time resolves uncertainty we present an empirical stochastic model of climate economy interactions and present results on the tension between postponing control until more is known vs acting now before irreversible climate change takes place uncertainty in our model is in the damage caused by global warming the results suggest that a temporary carbon tax may dominate a permanent one because a temporary tax may induce increased flexibility

protectionary bias in agriculture a pure economic argument abstract empirical evidence suggests that the agricultural sector in the developed countries has enjoyed a greater degree of protection than the import competing manufacturing sectors usually this is attributed to strong farm lobbies and hence on political factors we provide a theoretical model and a possible explanation of this phenomenon based on purely economic arguments two importables are accommodated in a three good three factor model of trade and production one is a labor intensive manufacturing good and the other is an agricultural commodity this captures the trade pattern of a typical industrialized country with an agricultural sector such as europe and the usa we show that uniform tariffs in agriculture and labor intensive manufacturing will definitely hurt the land owners in real terms and may reduce their absolute return hence if there has to be protection it has to be biased in favor of agriculture

estimation of the depreciation rate of physical and r d capital in the u s total manufacturing sector i introduction numerous studies on production and cost the sources of productivity and endogenous growth have recognized the pivotal role of the physical capital stock studies at various levels of aggregation over assets and industries have emphasized the crucial role of investment in plant and equipment in the growth of demand and productive capacity it is clearly recognized by economists and policymakers that knowledge capital approximated by rd 1986 to measure the depreciation rates of the stock of rd 1980 in the literature on dynamic demand models such an approach was first adopted by epstein and denny 1980 and more recently by kollintzas and choi 1985 for a single capital good and on a theoretical level in bernstein and nadiri 1987a 1987b the paper is organized as follows the specification of the model is presented in section ii section iii is devoted to a discussion of the data and to the presentation of the parameter estimates of the model in section iv we present the empirical results for the depreciation rates for physical and r d capital and compare them with those reported in the literature we compare the physical capital stock estimates generated by our model with the official capital stock estimates produced by u s department of commerce bureau of economic analysis in this section we also present our estimates of the decomposition of gross investment into replacement and expansion investment for both physical and r d capital these decompositions are important from the vantage point of public policy analysis

learning and climate feedbacks optimal climate insurance and fat tails we study the effect of potentially severe climate change on optimal climate change policy accounting for learning and uncertainty in the climate system in particular we test how fat upper tailed uncertainty over the temperature change from a doubling of greenhouse gases the climate sensitivity affects economic growth and emissions policy in addition we examine whether and how fast uncertainties could be diminished through bayesian learning our results indicate that while overall learning is slow the mass of the fat tail diminishes quickly since observations near the mean provide evidence against fat tails we denote as partial learning the case where the planner rejects high values of the climate sensitivity with high confidence even though significant uncertainty remains fat tailed uncertainty without learning reduces current emissions by 38 relative to certainty indicating significant climate insurance or paying to limit emissions today to reduce the risk of very high temperature changes is optimal however learning reduces climate insurance by about 50 the optimal abatement policy is strongly influenced by the current state of knowledge even though greenhouse gas ghg emissions are difficult to reverse non fat tailed uncertainty is largely irrelevant for optimal emissions policy

oligopolistic competition and economic welfare a general equilibrium analysis of entry regulation and tax subsidy schemes abstract two contributions to the general equilibrium analysis of an oligopolistic economy with free entry are intended first we generalize the excess entry theorem to the effect that a marginal decrease in the number of oligopolistic firms from the free entry equilibrium level improves economic welfare second we explore the pareto improving tax subsidy schemes in an oligopolistic economy several self financing and pareto improving tax subsidy schemes will be identified in contrast with the preceding analysis by atkinson and stiglitz which focused on the long run incidence of corporate taxation we analyse the short run as well as long run welfare implications of various policies under generalized conditions

cost benefit analysis under uncertainty a note on weitzman s dismal theorem abstract weitzman s 2009 famous dismal theorem argues that fat tails in the distribution of warming may pose problems for cost benefit analysis as it may imply that society might be willing to exchange today s consumption for future consumption at an infinite rate his analysis is based on the stochastic discount factor we show that in situations in which the stochastic discount factor is applicable it is optimal for society to devote only a finite amount of resources to protect against climate change for general assumptions on the investment returns cost benefit analysis must consider the joint distribution of the marginal utility of future consumption and marginal returns to investment in the different future states of nature we explore the range of situations under which challenges for applying cost benefit analysis under uncertainty remain

search and active learning with correlated information empirical evidence from mid atlantic clam fishermen this paper examines search with active learning and correlated information we first develop a simple model to show how correlation affects the decision to acquire information a unique data set on fishing site choice by mid atlantic clam fishermen is used to test the model predictions results find that clam fishermen search new sites when the catch at familiar sites declines i e when the opportunity cost of gathering information is low and also when catch at familiar sites is on the rise search following a catch decline occurs at spatially distant sites whereas search following a catch increase occurs at nearby sites correlated learning is crucial for explaining the site choice patterns in our data these results provide new insights that may extend to a variety of economic search problems where correlated learning is important

a rational economic model of paygo tax rates abstract we argue that paygo rates are determined by a representative agent and a benevolent government jointly maximizing the expected life time utility of the agent the distributions of labor and capital income are calculated from national data on real gdp real wages and the real return to capital since 1950 with uniform risk aversion predicted rates explain 83 of the variance of observed rates the globalization of capital markets would lead to convergence of paygo rates our results are immune to crises like 2008

uncertainty learning and heterogeneity in international environmental agreements this paper concerns the formation of international environmental agreements under uncertainty about environmental damage with different models of learning complete learning partial learning or no learning the results of the existing literature are generally pessimistic the possibility of either complete or partial learning generally reduces the level of global welfare that can be achieved from forming an iea relative to no learning that literature regards uncertainty as a parameter common to all countries so that countries are identical ex ante as well as ex post in this paper we extend the literature to the case where there is no correlation between damage costs across countries each country is uncertain about a particular parameter in our case the benefit cost ratio drawn from a common distribution but ex post each country s realized parameter value is independently drawn consequently while countries remain identical ex ante they may be heterogeneous ex post we show that this change reinforces the negative conclusions about the effects of partial learning on international environmental agreements but under certain conditions moderates the negative conclusions about the effects of complete learning

social security and risk sharing abstract in this paper we identify conditions under which the introduction of a pay as you go social security system is ex ante pareto improving in a stochastic olg economy with capital accumulation and land we argue that these conditions are consistent with realistic specifications of the parameters of the economy in our model financial markets are complete and competitive equilibria interim pareto efficient therefore a welfare improvement can only be obtained if agents welfare is evaluated ex ante and arises from an improvement in intergenerational risk sharing we also examine the optimal size of a given social security system as well as its optimal reform

trade liberalization in oligopolistic competition with unemployment a general equilibrium analysis this paper examines the short and long run effects of partial trade liberalization through relaxation of quantity restrictions in an oligopolistically competitive economy with unemployment while the short run effects of the liberalization policy are ambiguous its long run impacts are clear the policy dampens the price of the imported goods raises firms output and reduces the number of firms furthermore the policy lowers the unem ployment ratio and hence improves welfare when the economy suffers from sector specific unemployment whereas the policy may aggravate underemployment and thus may lower welfare for a labour surplus economy

rare disasters asset prices and welfare costs a representative consumer model with epstein zin weil preferences and i i d shocks including rare disasters accords with observed equity premia and risk free rates if the coefficient of relative risk aversion equals 3 4 if the intertemporal elasticity of substitution exceeds one an increase in uncertainty lowers the price dividend ratio for equity and a rise in the expected growth rate raises this ratio calibrations indicate that society would willingly reduce gdp by around 20 percent each year to eliminate rare disasters the welfare cost from usual economic fluctuations is much smaller though still important corresponding to lowering gdp by about 1 5 percent each year

does social security privatization produce efficiency gains while privatizing social security can improve labor supply incentives it can also reduce risk sharing we analyze a 50 privatization using an overlapping generations model where heterogeneous agents with elastic labor supply face idiosyncratic earnings shocks and longevity uncertainty when wage shocks are insurable privatization produces about 18 100 of extra resources for each future household after all transitional losses have been compensated for with lump sum taxes when wages are not insurable privatization reduces efficiency by about 2 400 per future household we check the robustness of these results to different model specifications as well as policy reforms and arrive at several surprising conclusions first privatization performs better in a closed economy where interest rates decline with capital accumulation than in an open economy second privatization also performs better when an actuarially fair private annuity market does not exist third government matching of private contributions on a progressive basis is not very effective at restoring efficiency and can actually cause harm

buying greenhouse insurance the economic costs of carbon dioxide emission limits in recent years a growing concern that the increasing accumulation of greenhouse gases will lead to undesirable changes in global climate has resulted in a number of proposals both in the united states and internationally to set physical targets for reducing greenhouse gas emissions but what will these proposals cost based on the authors earlier ground breaking work buying greenhouse insurance outlines a way to think about greenhouse effect decisions under uncertainty it describes an insightful model for determining the economic costs of limiting carbon dioxide emissions produced by burning fossil fuels and provides a solid analytical base for rethinking public policy on the farreaching issue of global warming manne and richels present region by region estimates of the costs that would underlie an international agreement using a computer model known as global 2100 they analyze the economic impacts of limiting c02 emissions under alternative supply and conservation scenarios the results clearly indicate that a reduction in emissions is not the sole policy response to potential climate change following a summary of the greenhouse effect its likely causes and possible consequences manne and richels take up issues that concern the public at large they provide an overview of global 2100 look at how the u s energy sector is likely to evolve under businessas usual conditions and under carbon constraints and describe the concept of greenhouse insurance they consider possible global agreements including an estimate of benefits that might result from trading in an international market in emission rights they conclude with a technical description directed toward modeling specialists alan manne is professor of operations research at stanford university richard richels is director of the energy analysis and planning department at the electric power research institute

intergenerational risk sharing and fiscal policy abstract risk sharing implications of alternative fiscal policies are compared in a stochastic production economy with overlapping generations ex ante efficiency is shown to be achievable with optimal transfers regardless of distributional concerns for crra preferences stylized real world policies notably safe debt and safe pensions are found inefficient in the direction of imposing not enough productivity risk on retirees and too much on future generations safe transfers can be rationalized as efficient if preferences display age increasing risk aversion such as habit formation the ubiquity of safe transfers suggests that governments treat the young as more risk tolerant than older cohorts

risk aversion wealth and background risk we use household survey data to construct a direct measure of absolute risk aversion based on the maximum price a consumer is willing to pay for a risky security we relate this measure to consumer s endowments and attributes and to measures of background risk and liquidity constraints we find that risk aversion is a decreasing function of the endowment thus rejecting cara preferences we estimate the elasticity of risk aversion to consumption at about 0 7 below the unitary value predicted by crra utility we also find that households attributes are of little help in predicting their degree of risk aversion which is characterized by massive unexplained heterogeneity we show that the consumer s environment affects risk aversion individuals who are more likely to face income uncertainty or to become liquidity constrained exhibit a higher degree of absolute risk aversion consistent with recent theories of attitudes toward risk in the presence of uninsurable risks jel d1 d8

tariffs foreign capital and immiserizing growth with urban unemployment and specific factors of production abstract in this note we show that a recent observation of brecher alejandro as regards tariff induced capital inflows essentially extends to a setting with urban unemployment three factors of production and a variety of labor market conditions in the urban sector

monopolistic competition nonhomotheticity and the stability of the chamberlinian tangency solution the focal point in the recent literature on international trade and monopolistic competition is to recast the chamberlinian partial equilibrium theory in a general equilibrium framework using a similar setting this paper asks whether the chamberlinian tangency solution is stable under general equilibrium paradoxical results follow when entry occurs profit per firm can increase and the tangency solution can be unstable a necessary and sufficient condition for stability is obtained the concepts of average and marginal factor intensities play an important role in obtaining the stability copyright 1990 by economics department of the university of pennsylvania and the osaka university institute of social and economic research association

scientific progress and irreversibility an economic interpretation of the precautionary principle abstract we consider the problem of the optimal use of a good whose consumption can produce damages in the future scientific progress is made over time that provides information on the distribution of the intensity of damages we show that this progress induces earlier prevention effort only if prudence is larger than twice absolute risk aversion this paper thus identifies the class of quite restrictive but plausible conditions such that scientific uncertainties justify an immediate reduction of the consumption of a potentially toxic substance

foreign capital inflows and welfare in an economy with imperfect competition abstract this paper examines the resource allocational and welfare effects of exogenous inflows of foreign capital in a general equilibrium model with oligopolistic competition and unemployment although the welfare impact for the short run is ambiguous and dependent upon the strength of excess profits and scale economies relative to unemployment in manufacturing in the long run additional inflows of foreign capital always improve national welfare with capital mobility hence attracting foreign capital remains a sound policy for economies characterized by imperfect competition scale economies and regional unemployment

tariffs quotas and voluntary export restraints with and without internationally mobile capital this paper presents a general framework for comparing the effects of tariffs quotas and vers voluntary export restraints both with and without international capital mobility expressions for the shadow price of foreign exchange and the shadow price of capital under each type of trade restriction are derived and it is shown that although international capital mobility raises the welfare cost of tariff protection it lowers the welfare cost of quantitative restrictions in most cases the effects of exogenous shocks in the presence of quotas are intermediate between those in the presence of tariffs and those in the presence of vers tarifs douaniers contingentements et restrictions volontaires d l exportation quand le capital est ou n est pas mobile internationalement l auteur presente un cadre general d analyse qu il utilise pour comparer les effets de tarifs douaniers de contingentements et de restrictions volontaires a l exportation dans des contextes ofu le capital est ou n est pas mobile internationalement l auteur derive le prix fictif du change etranger et le prix fictif du capital sous l un et l autre types de restrictions au commerce et montre que meme si la mobilite internationale du capital augmente le cofut en terme de bien etre de la protection tarifaire elle reduit le cofut en terme de bien etre des restrictions sur les quantites echangees dans tous les cas les effets de chocs exogenes quand des contingentements existent sont toujours dans la fourchette entre ceux qu on observe quand des tarifs douaniers existent et ceux qui prevalent quand des restrictions volontaires i l exportation existent

fat tailed risk about climate change and climate policy this paper investigates the role of emissions control in welfare maximization under fat tailed risk about climate change we provide a classification of fat tails and discuss the effect of fat tailed risk on climate policy one of the main findings is that emissions control may prevent the strong tail effect from arising at least under some conditions such as bounded temperature increases low risk aversion low damage costs and bounded utility function more specifically the fat tailed risk with respect to a climate parameter does not necessarily lead to an unbounded carbon tax in this case the basic principle of cost benefit analysis maintains its applicability

on the harris todaro model with intersectoral capital mobility n b professor neary was based at trinity college dublin when this article was first published the full text of the article is not available in ora at this time citation neary j p 1981 on the harris todaro model with intersectoral capital mobility economica 48 191 219 234

bayesian learning growth and pollution abstract environmental problems such as climate change have great uncertainties current expectations are that uncertainties about climate change will be resolved quickly we examine this hypothesis theoretically and computationally we consider bayesian learning about the relationship between greenhouse gas levels and global mean temperature changes a key uncertainty learning is non trivial because of a stochastic shock to the realized temperature we find theoretically the expected learning time which is related to the variance of the shock and the emissions policy implying a tradeoff between the benefits of controlling emissions and information we imbed the learning model into an optimal growth model with a climate sector and solve the resulting dynamic program we find computationally that learning takes on average over 90 yr far longer than currently believed

social security and demographic shocks an overlapping generations model of social security with shocks to the productivity of labor and capital and demographic shocks is studied we focus attention on stationary long run allocations an allocation is interim optimal if there does not exist another feasible allocation that improves the expected welfare of all generations computed conditionally on the state of the world when they are born we characterize the set of interim optimal allocations and study the equilibria associated with various institutional forms of social security from the point of view of this optimality criterion we obtain the analogs of the two traditional welfare theorems of microeconomic theory assume that there exists a financial asset in fixed quantity which supports some non null intergenerational transfers then the rational expectations equilibrium allocation of this economy is interim optimal conversely any stationary interim optimal allocation can be supported by such an equilibrium with adequate lump sum transfers

learning by doing and the value of optimal experimentation abstract recent research on learning by doing has provided the limit properties of beliefs and actions for a class of learning problems in which experimentation is an important aspect of optimal decision making however under these conditions the optimal policy cannot be derived analytically because bayesian learning about unknown parameters introduces a nonlinearity in the dynamic optimization problem this paper utilizes numerical methods to characterize the optimal policy function for a learning by doing problem that is general enough for practical economic applications the optimal policy is found to incorporate a substantial degree of experimentation under a wide range of initial beliefs about the unknown parameters dynamic simulations indicate that optimal experimentation dramatically improves the speed of learning and the stream of future payoffs furthermore these simulations reveal that a policy which separates control and estimation and does not incorporate experimentation frequently induces a long lasting bias in the control and target variables while these sequences tend to converge steadily under the optimal policy they frequently exhibit non stationary behavior when estimation and control are treated separately

the climate change learning curve abstract the purpose of this paper is to confront economic models of climate change with the reality that limited information exists with which to form expectations about the evolution of the climate a key element in the tension between those who believe we should impose aggressive climate change mitigation policies and those who do not is the question of if we are merely in a long period of shock induced above average temperatures or if observed increases in temperature are a result of carbon emissions this paper characterizes learning dynamics resulting from the use of observations of temperature to update beliefs about two key characteristics of global climate the persistence of natural trends and the sensitivity of temperature to atmospheric carbon levels this paper shows that contrary to predictions in the literature that uncertainty may be resolved very quickly the time to learn the true processes may be in the order of thousands of years further this paper shows the effects of uncertainty on the likelihood that observations from the statistical record lead to important estimate and policy errors

a portfolio approach to the optimal funding of pensions abstract fully funded pension systems are advocated for their higher rate of return but this return is typically risky using a simple mean variance model we find that mixed funded unfunded systems are desirable in this setting because they enable risk diversification

on modeling and interpreting the economics of catastrophic climate change with climate change as prototype example this paper analyzes the implications of structural uncertainty for the economics of low probability high impact catastrophes even when updated by bayesian learning uncertain structural parameters induce a critical tail fattening of posterior predictive distributions such fattened tails have strong im plications for situations like climate change where a catastrophe is theoretically possible because prior knowledge cannot place sufficiently narrow bounds on overall damages this paper shows that the economic consequences of fat tailed structural uncertainty along with unsureness about high temperature damages can readily outweigh the effects of discounting in climate change policy analysis

measuring risk attitudes in a natural experiment data from the television game show lingo we use data from a television game show involving elementary lotteries as a natural experiment to measure risk attitudes unique features of our data set are the substantial monetary stakes and the large sample size crra and cara utility specifications perform approximately equally well we find robust evidence of substantial risk aversion extensions of the basic model which allow for a separate utility flow purely from playing the game or for decisions based on decision weights instead of actual probabilities raise the estimated degree of risk aversion