Just one year after 2014 set a record as the hottest year in the historical record, 2015 is on track to beat it by a large margin, possibly signaling a return to a sustained period of rapid global warming.
The National Oceanic and Atmospheric Administration, a federal agency that tracks worldwide temperatures, announced Wednesday that last month had been the hottest September on record and that the January-to-September period had also been the hottest since 1880. Scientists say the mathematical odds are now overwhelming that the full year will be the hottest ever recorded.
The immediate cause is a strong El Niño weather pattern, in which the ocean releases immense amounts of heat into the atmosphere. But temperatures this year are running far ahead of those during the last strong El Niño, in 1997 and 1998, and scientists said that would likely not have happened without an underlying trend of warming caused by human emissions of greenhouse gases. The El Niño phenomenon and the accompanying heat are already roiling weather patterns worldwide, likely contributing to dry weather and forest fires in Indonesia, to drought in Ethiopia, and to a developing food emergency across swaths of Africa.
Those effects are likely to intensify in coming months, with the potential for heavy storms, mudslides and floods in California, drought in Australia and in parts of Brazil, and many other weather-related disasters.
Earlier this year, the global warmth contributed to a spring heat wave in India and Pakistan that may have killed several thousand people, with temperatures hitting 118 degrees Fahrenheit in parts of India.
Forecasters have been issuing warnings about a strong El Niño for many months. The coming few months will thus test whether governments, and the global relief agencies that support poor countries, have done a competent job of preparing, particularly to provide food relief for hard-hit regions.
"The warning is out," said Richard Seager, a climate scientist at the Lamont-Doherty Earth Observatory of Columbia University, in New York. "The world has had time to plan for this."
