Reuters: The coldest winter days in Russia and Canada have become up to 4 Celsius (7 Fahrenheit) milder since the 1950s in an extreme sign of climate change, the British Meteorological Office said on Wednesday. A study of daily minimum and maximum temperatures said that a trend towards warmer nights and hotter days was set to bring more heatwaves and shifts in crop growing seasons. "Minimum temperatures have seen the biggest increases, most notably over Russia and Canada, where …