Expecting the Unexpected: Emissions Uncertainty and Environmental Market Design".

We study potential equilibria in California’s 2013-2020 cap-and- trade market for greenhouse gasses (GHGs) based on information available before the market started. We find large ex ante uncer- tainty in business-as-usual emissions, and in the abatement that might result from non-market policies, compared to the market- based variation that could plausibly result from changes in al- lowance prices within a politically acceptable range. This implies that the market price is very likely to be determined by an admin- istrative price floor or ceiling. Comparable analysis seems likely to reach similar conclusions in most cap-and-trade markets for GHGs, consistent with outcomes to date in such markets.