Last year, Eurex, the Swiss-German derivatives exchange, started publishing temperature indexes for 30 European cities as a prelude to its entrance into the exchange-traded weather derivatives market. But it soon changed its plans. “Weather derivatives are a cute and nice idea,” a Eurex spokesman said, “but there is no customer demand for the product.”

Now it has made another dramatic U-turn. Eurex is again considering launching exchange-traded weather derivatives, although it still has