That has now risen to 2.21 percent, which is quite a large swing by the standards of the generally staid bond market.

Here’s an important wrinkle: While economists often talk about those numbers as a measure of investors’ inflation expectations, they can just as easily be a measure of investors’ level of worry about inflation risk. What’s the difference? One is about what seems likely to happen, while the other is about an increase in the chances of an unlikely — but costly — outcome.

Back to the drought metaphor: The farmers might still think that another dry year is the most likely result, but if recent showers make them worry more about the risk of flooding, and they all try to buy insurance at the same time, this drives up the price. That seems to be what has happened in the last two months in the market for inflation-protected bonds, which essentially function as insurance against future rises in prices.

This framework also helps explain why there have been such big swings in financial markets lately.

Analysts at Deutsche Asset Management noted recently that government bonds from the United States and Germany — generally considered some of the world’s bedrock safe assets — have been more volatile lately than bonds issued by emerging market countries like Indonesia and Mexico.

And the Standard & Poor’s 500 has moved more than 1 percent on eight of 16 trading days in February thus far, which doesn’t make much sense if you’re looking for fundamentals-based reasons for such big moves in stock prices. It makes more sense if you believe that investors are trying to extrapolate from tiny fragments of information the potential risk of a radically different economic and financial market environment in the years ahead.

The swings in stock prices appear to be intimately linked to movement in long-term interest rates, which in turn hinges on those expectations of inflation and how the Federal Reserve will respond if inflation does rise.

On Wednesday, for example, the stock market had been on track for a sharply positive day until the Fed released minutes of its last policy meeting at 2 p.m. Soon after, the stock market plunged and bond yields rose, as investors evidently concluded that the Fed was inclined toward a somewhat faster rate of interest rate increases than had been assumed.