There is a lot we know about climate change, but there is also a lot we don't know. Even if we knew how much CO2 will be emitted over the coming decades, we wouldn't know how much temperatures will rise as a result. And even if we could predict the extent of warming that will occur, we can say...

I use a simple SIR model, augmented to include deaths, to elucidate how pandemic progression is affected by the control of contagion, and examine the key trade-offs that underlie policy design. I illustrate how the cost of reducing the "reproduction number" R0 depends on how it changes the...

How does the sustainable level of consumption depend on productivity growth and the size and growth rate of the population? What is the effect of uncertainty over these growth rates? I address these questions using a model in which productivity and population growth are stochastic, and social...

We study the effects of aggregate and idiosyncratic uncertainty on the entry of firms, total investment, and prices in a competitive industry with irreversible investment. We first use standard dynamic programming methods to determine firms' entry decisions, and we describe the resulting...

Forestation is viewed as an important means of removing CO₂ from the atmosphere and thereby reducing net CO₂ emissions. But how much CO₂ can be removed, and at what cost? Focusing on forested and forestable areas in South America, and using spatially disaggregated data, we estimate a...

Modern investors face a high-dimensional prediction problem: thousands of observable variables are potentially relevant for forecasting. We reassess the conventional wisdom on market efficiency in light of this fact. In our model economy, which resembles a typical machine learning setting, N...

We view sustainability as a requirement that welfare should not be expected to decline over time. We impose this requirement as a prior constraint on the consumption-savings-investment problem, and study its implications for saving, risky investment, and the social discount rate. The constraint...

We study cointegrating relationships among fiscal variables and output and use them to introduce a new measure of the government's fiscal position. In the US since World War II, we find that the primary surplus-GDP ratio and the government debt-GDP ratio are nonstationary, which invalidates...