By SETH BORENSTEIN, AP Science Writer In just 50 years, 2 billion to 3.5 billion people, mostly the poor who can’t afford air conditioning, will be living in a climate that historically has been too hot to handle, a new study said. With every 1.8 degree (1 degree Celsius) increase in global average annual temperature from man-made climate change, about a billion or so people will end up in areas too