The extreme heat and related climate disturbances mean that delegates to a global-climate conference scheduled for Paris in early December will almost certainly be convening as weather-related disasters are unfolding around the world.

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Global temperatures are running far above last year’s record-setting level, all but guaranteeing that 2015 will be the hottest year in the historical record.

The National Oceanic and Atmospheric Administration (NOAA), the U.S. agency that tracks worldwide temperatures, announced Wednesday that last month had been the hottest September on record, and, in fact, took the biggest leap above the previous September that any month has displayed since 1880, when tracking began at a global scale. The agency also announced that the January-to-September period had been the hottest such span on the books.

The extreme heat and related climate disturbances mean that delegates to a global-climate conference scheduled for Paris in early December will almost certainly be convening as weather-related disasters are unfolding around the world, putting them under greater pressure to reach an ambitious deal to limit future emissions and slow the temperature increase.

The immediate cause of the record-breaking warmth is a strong El Niño weather pattern, in which the ocean releases immense amounts of heat into the atmosphere. But temperatures are running so far ahead of those during the last strong El Niño, in 1997 and 1998, that scientists said records would not be occurring without an underlying trend caused by emissions of greenhouse gases.

“The bottom line is that the world is warming,” said Jessica Blunden, a climate scientist with NOAA, in Asheville, N.C.

She pointed to measurements in several of the world’s ocean basins, where surface temperatures are as much as three degrees above the 20th-century average, a substantial increase.

“We’re seeing it all across the Indian Ocean, in huge parts of the Atlantic Ocean, in parts of the Arctic oceans,” Blunden said.

The combined effects of El Niño and greenhouse warming are already roiling weather patterns worldwide, likely contributing to dry weather and forest fires in Indonesia, to an incipient drought in Australia and to a developing food emergency across parts of Africa, including a severe drought in Ethiopia. Those effects are likely to intensify in coming months as the El Niño reaches its peak and then gradually subsides.

Past patterns suggest the El Niño will send unusual amounts of rain and snow to the American Southwest and to California, offering some relief for that parched state but also precipitating floods and mudslides.

Earlier this year, the global warmth contributed to a spring heat wave in India and Pakistan that killed many people, possibly several thousand, with temperatures hitting 118 degrees in parts of India. The effects on the natural world have also been severe, with extreme ocean temperatures bleaching coral reefs around the world.

El Niño originates in the eastern tropical Pacific Ocean, when normal weather patterns shift in a way that allows the ocean to release large amounts of stored-up heat into the atmosphere. That perturbs atmospheric waves that can travel thousands of miles, redistributing heat and moisture around the globe.

Scientists have long wondered whether human-induced global warming would alter the frequency or severity of El Niños, but so far, that does not seem the be the case.