The activist investors are on the tarmac at Emerson Electric Co.  D.E. Shaw Group on Tuesday released a letter calling for the $42 billion industrial company to spin off its climate division and make productivity and corporate-governance improvements, including culling its fleet of eight corporate jets and a helicopter. The public pressure follows reports late last month that D.E. Shaw was seeking a breakup of the company and Emerson’s subsequent announcement that it would review its operations....