Papers

July 2021 | Working Paper

New NBER Working Paper: “Climate Change Uncertainty Spillover in the Macroeconomy”

Michael Barnett, William Brock, and Lars Peter Hansen

Abstract

The design and conduct of climate change policy necessarily confronts uncertainty along multiple fronts. We explore the consequences of ambiguity over various sources and configurations of models that impact how economic opportunities could be damaged in the future. We appeal to decision theory under risk, model ambiguity and misspecification concerns to provide an economically motivated approach to uncertainty quantification. We show how this approach reduces the many facets of uncertainty into a low-dimensional characterization that depends on the uncertainty aversion of a decision-maker or fictitious social planner. In our computations, we take inventory of three alternative channels of uncertainty and provide a novel way to assess them. These include i) carbon dynamics that capture how carbon emissions impact atmospheric carbon in future time periods; ii) temperature dynamics that depict how atmospheric carbon alters temperature in future time periods; iii) damage functions that quantify how temperature changes diminish economic opportunities. We appeal to geoscientific modeling to quantify the first two channels. We show how these uncertainty sources interact for a social planner looking to design a prudent approach to the social pricing of carbon emissions.

Journal: forthcoming in the Annual Review of Economics|Tags: Climate, Uncertainty|
June 2021 | Preliminary Paper

New Preliminary Paper: “Central Banking Challenges Posed by Uncertain Climate Change and Natural Disasters”

Lars Peter Hansen

Abstract

Climate change poses an important policy challenge for governments around the world. The challenge is made all that much more difficult because of the multitude of potential policymakers involved in setting the policy worldwide. What then should be the role of central banks? How are climate change concerns similar or distinct from those of other natural disasters? Clarity of ambition and execution will help to ensure that central banks maintain credibility by adhering to their mandated roles they retain their critically important distance from the political arena.

Tags: Climate, Uncertainty, Uncertainty and Valuation|
May 2021 | Preliminary Paper

New Preliminary Paper: “Confronting Uncertainty in the Climate Change Dynamics”

Michael Barnett, William Brock, and Lars Peter Hansen

Abstract

In designing policy to combat climate change, there are many calls for immediate action. However, there has also been some apprehension expressed about acting prematurely based on existing limits to our understanding of the timing and the quantitative magnitude of climate change and its impact on economic and social outcomes. We approach this problem from the perspective of a decision maker who confronts uncertainty in a setting in which there will be future information about damage severity. The value of further empiricism in the near term will be limited as the climate-economic system moves into uncharted territory. The decision maker’s concerns about uncertainty go beyond the standard risk considerations. There is ambiguity over how much credibility to assign to alternative models of climate change and economic damages and all such models are potentially misspecified. These uncertainties add to the challenge of projecting how economic damages in the future will be enhanced with current and future fossil fuel emissions. The solution to the decision problem we pose shows some initial caution until future damage possibilities are more fully revealed. With the more refined information, the decision maker may be either more wary of climate change, or more bullish, and act accordingly depending on what is revealed. We provide a quantitative illustration drawing in part on cross-model ambiguity revealed by pulse experiments conducted by geoscientists.

Tags: Climate, Uncertainty|Export BibTeX >

Abstract

In designing policy to combat climate change, there are many calls for immediate action. However, there has also been some apprehension expressed about acting prematurely based on existing limits to our understanding of the timing and the quantitative magnitude of climate change and its impact on economic and social outcomes. We approach this problem from the perspective of a decision maker who confronts uncertainty in a setting in which there will be future information about damage severity. The value of further empiricism in the near term will be limited as the climate-economic system moves into uncharted territory. The decision maker’s concerns about uncertainty go beyond the standard risk considerations. There is ambiguity over how much credibility to assign to alternative models of climate change and economic damages and all such models are potentially misspecified. These uncertainties add to the challenge of projecting how economic damages in the future will be enhanced with current and future fossil fuel emissions. The solution to the decision problem we pose shows some initial caution until future damage possibilities are more fully revealed. With the more refined information, the decision maker may be either more wary of climate change, or more bullish, and act accordingly depending on what is revealed. We provide a quantitative illustration drawing in part on cross-model ambiguity revealed by pulse experiments conducted by geoscientists.

February 2021 | Working Paper

Uncertainty Spillovers for Markets and Policy

Lars Peter Hansen

Abstract:

We live in a world surrounded by uncertainty. In this essay, I show that featuring this phenomenon more in economic analyses adds to our understanding of how financial markets work and how best to design prudent economic policy. This essay explores methods that allow for a broader conceptualization of uncertainty than is typical in economic investigations. These methods draw on insights from decision theory to engage in uncertainty quantification and sensitivity analysis. Uncertainty quantification in economics differs from most sciences because there is uncertainty both from the perspective of an external observer and from people and enterprises within the model. I illustrate these methods in two example economies in which the understanding of long-term growth is limited. One example looks at uncertainty ramifications for fluctuations in financial markets, and the other considers the prudent design of policy when the quantitative magnitude of climate change and its impact on economic opportunities is unknown.

View Paper on SSRN

Journal: forthcoming in the Annual Review of Economics|Tags: Uncertainty|
February 2021 | Working Paper

Making Decisions Under Model Misspecification

Simone Cerreia-Vioglioa, Lars Peter Hansen, Fabio Maccheronia, and Massimo Marinacci

We use decision theory to confront uncertainty that is sufficiently broad to incorporate models as approximations.” We presume the existence of a featured collection of what we call “structured models” that have explicit substantive motivations. The decision maker confronts uncertainty through the lens of these models, but also views these models as simpli…fications, and hence, as misspeci…fied. We extend min-max analysis under model ambiguity to incorporate the uncertainty induced by acknowledging that the models used in decision-making are simplified… approximations. Formally, we provide an axiomatic rationale for a decision criterion that incorporates model misspeci…fication concerns.

Series Name: Becker Friedman Institute Working Paper Series |Tags: Uncertainty|
January 2021 | Article

Newly Published Paper in Proceedings of the National Academy of Sciences (PNAS) – “Rational Policymaking During a Pandemic”

Loïc Berger, Nicolas Berger, Valentina Bosetti, Itzhak Gilboa, Lars Peter Hansen, Christopher Jarvis, Massimo Marinacci, Richard D. Smith

Abstract:

Policymaking during a pandemic can be extremely challenging. As COVID-19 is a new disease and its global impacts are unprecedented, decisions need to be made in a highly uncertain, complex and rapidly changing environment. In such a context, in which human lives and the economy are at stake, we argue that using ideas and constructs from modern decision theory, even informally, will make policymaking more a responsible and transparent process.

 

Journal: PNAS|Tags: Uncertainty, Uncertainty and Valuation|
January 2021 | Preliminary Paper

New Preliminary Paper: “Robust Estimation and Inference when Beliefs are Subjective”

Xiahong Chen and Peter G. Hansen

Abstract

Applied researchers using structural models of economic dynamics under ratio-nal expectations (RE) often confront empirical evidence of misspecification. In this paper we consider a generic dynamic model that is posed as a vector unconditional moment restrictions. We suppose that the model is globally misspecified, and thus empirically flawed in a way that is not econometrically subtle. In RE models the expectations used in defining the moment conditions are both consistent with the beliefs of the economic agents within the model and population limit of the empirical distribution. We relax this assumption by allowing subjective beliefs to differ from rational expectations while still maintaining that the moment conditions are satisfied under the subjective beliefs of economic agents whose behavior is captured by the dynamic economic model. This form of misspecification alters econometric identifi-cation and inferences in a substantial way. The underlying parameter vector ceases to be identified and the subjective beliefs may unduly weak. Therefore, we explore the consequences of restricting the statistical divergence between subjective belief distortions and their RE counterparts. In so doing, we are lead to address some new econometric challenges.

December 2020 | Article

Newly Published Research in the Journal of Economic Theory: “Structured Ambiguity and Model Misspecification”

Lars Peter Hansen and Thomas J. Sargent

A decision maker is averse to not knowing a prior over a set of restricted structured models (ambiguity) and suspects that each structured model is misspecified. The decision maker evaluates intertemporal plans under all of the structured models and, to recognize possible misspecifications, under unstructured alternatives that are statistically close to them. Likelihood ratio processes are used to represent unstructured alternative models, while relative entropy restricts a set of unstructured models. A set of structured models might be finite or indexed by a finite-dimensional vector of unknown parameters that could vary in unknown ways over time. We model such a decision maker with a dynamic version of variational preferences and revisit topics including dynamic consistency and admissibility.

Journal: Journal of Economic Theory|Tags: Risk, Robustness and Ambiguity, Uncertainty|Export BibTeX >

@article{hansensargent:2018structured,
title={Structured Uncertainty and Model Misspecification},
author={Hansen, L. P. and Sargent, T. J.},
journal={SSRN Working Paper},
year={2018}
}

December 2020 | Article

Recently Published Paper in Proceedings of the National Academy of Sciences (PNAS) – “Robust Identification of Investor Beliefs”

Xiaohong Chen, Lars Peter Hansen and Peter G. Hansen

This paper develops a new method informed by data and models to recover information about investor beliefs. Our approach uses information embedded in forward-looking asset prices in conjunction with asset pricing models. We step back from presuming rational expectations and entertain potential belief distortions bounded by a statistical measure of discrepancy. Additionally, our method allows for the direct use of sparse survey evidence to make these bounds more informative. Within our framework, market-implied beliefs may differ from those implied by rational expectations due to behavioral/psychological biases of investors, ambiguity aversion, or omitted permanent components to valuation. Formally, we represent evidence about investor beliefs using a novel nonlinear expectation function deduced using model-implied moment conditions and bounds on statistical divergence. We illustrate our method with a prototypical example from macro-finance using asset market data to infer belief restrictions for macroeconomic growth rates.

Paper

Associated Jupyter Code 

Journal: PNAS|Tags: Uncertainty|
December 2020

Repercussions of Pandemics on Markets and Policy

Lars Peter Hansen

Abstract:

The COVID-19 pandemic that we are experiencing is both tragic and shocking. There is no question that, except in some Asian countries trained by prior infectious outbreaks, most policy makers around the world have been ill-prepared to respond to the crisis. The effects of the coronavirus on our mental and physical health has been indeed calamitous, and the economic and financial impacts for many have been truly unfortunate. Furthermore, the extreme nature of the event is challenging researchers to compile and interpret new evidence that is arriving at a rapid pace. The editors Hui Chen, Thierry Foucault, Jeffrey Pontiff, and Nikolai Roussanov and contributing authors are to be commended for assembling and collating a thought-provoking collection of papers. More time and study will be needed to fully sift through the evidence and to glean the lessons to be learned from this pandemic for policy makers and investors. But the evidence and insights in this volume are a very good start.

All papers of this volume are posted online on the Oxford University Press website.

Journal: The Review of Asset Pricing Studies|Publisher: Published Online by Oxford University Press|Tags: Uncertainty|