# Benth: Risk-neutral measure in incomplete markets

I am currently working on Benth and Benth "THE VOLATILITY OF TEMPERATURE AND PRICING OF WEATHER DERIVATIVES" and i am stuck at following paragraph at page 10, which is about risk-neutral measures in incomplete markets of weather derivatives:

"In order to derive a more explicit expression for the futures price, we need to specify the risk-neutral probability $$Q$$. Since temperature is not a storable commodity, the futures contracts can not be hedged and the market is therefore incomplete. A risk-neutral probability is by definition a probability measure $$Q\sim P$$ such that all tradeable assets in the market are martingales after discounting. Thus, all equivalent probabilities $$Q$$ will become risk-neutral probabilities. We specify a sub-family of probability measures $$Q$$ using the Girsanov transform: [...]"

Problem:
I do not understand why all equivalent probabilities are risk-neutral probabilities in incomplete markets?!

Thank you very much for your help!

The price of weather derivatives cannot simply be calculated using a hedging strategy, since the underlying is not tradable. We are therefore in an incomplete market. If we restrict the market to weather derivatives, the treasury bill with a risk-free interest rate $$r\in\mathbb{R}$$ is the only tradeable asset in the market. The discounted treasury bill price is $$1$$ and it is therefore a trivial martingale with respect to all equivalent measures. Thus, all equivalent probability measures $$\mathcal{Q}\sim \mathcal{P}$$ will become risk neutral probabilities.