Bloomberg: London’s fog, a fixture in the U.K. capital that led to the deaths of 4,000 people in 1952, may be on the wane, contributing to warmer temperatures. Why? Cleaner air. French-led scientists studied three decades of data from 342 weather stations across Europe and found that on average, the number of days where London visibility was lower than 2 kilometers (1.2 miles) has halved since 1980. The trend correlates with a fall in emissions of sulfur dioxide, a gas associated with burning …