Dynamic coherent risk measures

Monetary measures of risk like Value at Risk or Worst Conditional Expectation assess the risk of financial positions. The existing risk measures are of a static, one period nature. In this paper, I define dynamic monetary risk measures and I present an axiomatic approach that extends the class of coherent risk measures to the dynamic framework. The axiom of translation invariance has to be recast as predictable translation invariance to account for the release of new information. In addition to the coherency axioms, I introduce the axiom of dynamic consistency. Consistency requires that judgements based on the risk measure are not contradictory over time. I show that consistent dynamic coherent risk measures can be represented as the worst conditional expectation of discounted future losses where the expectations are being taken over a set of probability measures that satisfies a consistency condition.