By Justin Gillis, The New York Times, October 21, 2015
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 — and undermining political claims that global warming had somehow stopped.
The National Oceanic and Atmospheric Administration, the American 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 political 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 the records would not be occurring without an underlying trend caused by human 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 Fahrenheit above the 20th century average, a substantial increase when calculated over such large areas.
“We’re seeing it all across the Indian Ocean, in huge parts of the Atlantic Ocean, in parts of the Arctic oceans,” Dr. Blunden said in an interview. “It’s just incredible to me. I’ve never seen anything like this before.”
The combined effects of El Niño and greenhouse warming are already roiling weather patterns worldwide, probably 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 that 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. The California effects are not a certainty, experts said, but if they come, they are likely to be strongest in the latter part of the winter.
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, and many of them likely to suffer lasting damage.
Though worldwide in its consequences, 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.
The effects can be profound, with some research even suggesting that civil wars become more likely in tropical countries when they are under stress from an El Niño.
The World Food Program, a United Nations relief agency, is preparing for expanded operations across Africa, and appealing for donations. Harvests are down across large stretches of that continent, and the number of people going hungry in Ethiopia is likely to be in the millions in coming months, relief groups have estimated.
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 to be the case. “We have no reason at this point to think that El Niño itself is responding to the forcing from greenhouse gases,” Dr. Seager said. “You can think of them as independent and adding to each other.”
For much of the past decade, people who question established climate science have been claiming that global warming had stopped. Their argument depended on picking a particular base year — almost always 1998, the final year of the last strong El Niño — as their starting point.
But mainstream climate scientists said that was a statistically invalid cherry-picking of the data, and their analysis of the entire record showed that global warming never stopped — at most, the rise of surface temperatures slowed somewhat, even as the oceans continued to warm at a brisk pace.
The record-setting warmth of 2014 and 2015 has undermined the idea that the problem of greenhouse emissions had somehow solved itself, though some Washington politicians continue to repeat the claims. Climate scientists have not wavered in their view that the long-term temperature increase poses profound risks and that emissions must be brought under control.