Scientists struggle to explain record surge in global heat

Over the past two years, temperature records have been repeatedly shattered by a streak so persistent and puzzling it has tested the best-available scientific predictions about how the climate functions. Scientists are unanimous that burning fossil fuels has largely driven long-term global warming, and that natural climate variability can also influence temperatures one year to the next. But they are still debating what might have contributed to this particularly exceptional heat surge. Experts think changes in cloud patterns...