Earth’s winds of change . . .

QUESTION Could the jet stream stop? If it did, would the polar ice caps melt?

Jet streams are fast-flowing and meandering, but concentrated, air currents that circulate the earth. the northern polar jet stream is important for aviation and weather forecasting.

It forms a core of strong winds around five to seven miles above the earth’s surface, blowing from west to east.

It is driven by the temperature difference between air masses in the North Pole and the equator and the earth’s Coriolis force (a result of the earth’s rotation).

If climate science predictions are correct, then a rapid warming in the Arctic means the temperature difference between the two areas is decreasing. Some suggest this reduction in the temperature differential is robbing the jet stream of some of its strength.

there is no suggestion the jet stream will stop, although it may be meandering further afield, contributing to increasing temperature extremes. Perhaps there has been confusion with the Gulf Stream — ocean current driven by differences in temperature and salt content, the result of a phenomenon called thermohaline circulation.

Dr Ian Smith, Cambridge.

QUESTION Has a theatre understudy ever gone on to outshine the star?

Further to earlier answers, in a 2009 interview, elaine Paige related how, when she was in the chorus of the stage show hair (back in the Sixties), the principal and her understudy were both stricken ill and she was asked to take over the role. It was the start of her illustrious stage career. Gerald R. Kimber, Lymington, Hants.