Climate change is the topic of the day. The World Meteorological Organization tells us that the 2011-20 decade was the warmest on record. Earlier this year, the U.S. government re-joined the Paris Accord, and is proposing a range of new programs to mitigate the long-run impact of climate change. Now that a warming planet has made the Arctic increasingly navigable, national security specialists are concerned about geopolitical risks there. Thousands of economists have endorsed a carbon tax. Even central banks have joined together to form the Network for the Greening of the Financial System—a forum to discuss how to take account of climate change in assessing financial stability.

Against that background, last month, NYU Stern’s Volatility and Risk Institute (VRI) held a conference on finance and climate change. Speakers addressed issues ranging from the modeling and measurement of climate risk in finance to assessing its impact on the resilience of the financial system. In this post, we primarily focus on one of the central challenges facing policymakers and practitioners: what is the appropriate discount rate for evaluating the relative costs and benefits of investments in climate change mitigation that will not pay off for decades? We also comment briefly on several other issues in the rapidly growing field of climate finance research.

Past responses to the discount-rate question vary widely. Some observers call for a discount rate matching the high expected return on long-lived, risky assets—a number as high as 7%. This would imply a very low present value of benefits from investments to mitigate climate change, consistent with only modest current expenditures. Others postulate that climate change could lead to the extinction of humanity. For plausible discount rates, the specter of a nearly infinite loss means that virtually any level of mitigation investment is warranted (see, for example, Holt).

Recent climate finance research that we summarize here comes to the conclusion that over any reasonable horizon, the appropriate discount rate for computing the net present value of investments in climate change mitigation should be relatively low….