Why Air Conditioning Is a Life-Saver — and a Danger

Extreme heat recently melted roads in the U.K.; hit a record-shattering 120°F in Chino, Calif.; and led to more than 70 deaths in Quebec. These cases illustrate a vexing paradox for scientists and policymakers: air conditioning keeps people cool and saves lives but is also one of the biggest contributors to global warming.

Two new reports underscore the scale of the challenge. On July 16, Sustainable Energy for All, an NGO that is dedicated to clean energy and is affiliated with the U.N.