Record-breaking heatwaves in cities from Tulsa, Oklahoma, to Toronto, Canada; devastating floods in Russia and India, hundreds dead, millions affected. These are not gloomy scenarios put about by eco-warriors; when thousands of local weather records are simultaneously broken in many countries, you know something weird really is happening. But is it just a temporary glitch in the global weather machine, or has it gone permanently awry? Meteorologists lay much of the blame with the malfunctioning of a key part of that machine, the northern polar jet stream.To find out, two researchers at the University of Reading in England, Dr Tim Woollings and Dr Mike Blackburn, turned to sophisticated computer simulations of the atmosphere. Using 22 such simulations, developed by leading teams around the world, they compared the effect of raising global temperatures with the natural variation recorded since the late 1950s. In results recently published in the Journal of Climate, they found that - as expected - global warming does indeed affect the jet streams, pushing them closer to the poles.