What a Serbian cave tells you about the weather 2,500 years ago

IF YOU LIVE in northern Europe or North America, your partly on what the northern polar jet stream is up to. Jet streams are powerful and persistent winds that snake around the Earth from west to east, several miles above the surface. The meanderings of the northern polar jet stream can bring cold air down from the Arctic over the American Midwest, or send waves of Atlantic storms crashing into Ireland or Scandinavia.As with most sorts of weather, scientists suspect that the flow of the jet streams is being affected by climate change. Data from the past century and a half suggest that the northern jet stream has become stronger over that time. But a century is not all that long in climatic terms, and it is not entirely clear whether the strengthening is a natural phenomenon.