The National Oceanic and Atmospheric Administration's 2015 State of the Climate report unleashed a flood of statistics that should overwhelm whatever doubts remain of global warming's already startling impacts, scientists said Tuesday.
For the first time since record-keeping started, the average annual global temperature exceeded pre-industrial levels by more than 1 degree Celsius. Record to near-record warmth was common on every inhabited continent. Sea surface temperatures and heat content in the upper levels of the ocean also set records, as did sea level, which crept up to 2.75 inches above the 1993 level, when the satellite altimeter record started. Glaciers around the world retreated for the 36th year in a row, the report said.
"As I often point out now, the impacts of climate change are no longer subtle," said climate scientist Michael Mann, director of the Earth System Science Center at Penn State University. "They are playing out before us, in real time. The 2015 numbers drive that home."
The strong El Niño weather system in the Pacific played a role in many of the record statistics last year, but they are also signs that an overheated planet is reacting in alarming ways, according to Anders Levermann, a sea level rise expert with the Potsdam Climate Institute in Germany.
"Increasing the temperature of the planet will increase the risk of tipping of climatic systems like the West Antarctic ice sheet," he said. "Sea level is rising with every degree of warming that we induce by carbon emissions."
Levermann said even if those emissions were capped today, the sea would keep rising. "Each degree Celsius of warming adds about 8 feet to the eventual sea level rise that we are committed to in the long term," he said.
The report, released Tuesday, compiles work by more than 450 scientists from 62 countries who evaluated tens of thousands of measurements taken by land, ocean, ice and space-based instruments. It shows how the planet is being affected both by the temporary El Niño temperature surge and the long-term warming trend, said Thomas R. Karl, director of NOAA's National Centers for Environmental Information. Citing changes in the distribution of fish species in Arctic waters, Karl said the impacts of global warming are clearly having significant impact on life on this planet now.
Symptoms of a fevered planet referenced in the report include: record greenhouse gas concentrations in the atmosphere, extremes in the water cycle; impacts to Arctic animals and fish; unprecedented algae blooms in the Northwest Pacific; and the global decline of ice and snow cover.
NOAA climatologist Jessica Blunden said Tuesday that signs of climate change in 2015 included widespread drought, with about 30 percent of the world's land surface affected by abnormal dryness — the largest percentage since at least the 1950s. According to Blunden, there were extreme drought conditions on every continent last year. The hardest hit areas included nearly all of Australia, southern Africa, Central America and the Caribbean, the western U.S. and the Amazon basin.
"There were three Category 4 tropical storms at the same time in the Eastern Pacific, the first time that's happened in any ocean basin," Blunden said. "That's consistent with El Niño, but also what we expect to see in a warming world."
The year was also marked by several deadly heatwaves. At least 1,000 people died in June in Karachi, Pakistan's largest city. Several months of extreme summer heat in western Europe resulted in 1,250 deaths, making it the third deadliest natural catastrophe of 2015. That was according to a separate report compiled by Munich RE, a re-insurance firm that specializes in analyzing natural disasters and climate-related risks.
The 2015 heatwaves were characterized not only by extreme daytime heat, but by high nighttime temperatures, which makes them more dangerous because people have less chance to cool down, Blunden said. Nights have been warming much faster than days during the global warming era, according to a study released earlier this year in the International Journal of Climatology.
Some of the biggest signs of the changing climate continue to come from the Arctic, where temperatures are warming twice as fast as the global average. In the Barents Sea, warm-water fish are displacing cold-water species, said U.S. Army Corps of Engineers researcher Jackie Richter-Menge, who edited the Arctic chapter of the report. She also highlighted unusual melting in northern Greenland linked with a wobbly jet stream and a significant warming of permafrost in the far northern reaches of the Arctic.
Several scientists said not to give El Niño too much credit for the global temperature surge.
"I think some people think it's warm because of the El Niño and assume that it's not warm because of global warming," said Phil Jones, research director of the Climatic Research Unit at the University of East Anglia (UK).
"The key thing is the global scale of the warmth in 2015."
After strong El Niño events, "the second year is warmer, so although 2015 is far and away the warmest year, 2016 will be warmer still," he said. "We all live locally, so we can't experience the global average. We need massive efforts like SOTC to bring this largest of scales to our attention."
Levermann of the Potsdam Institute said that as a climate scientist it's interesting to see some of the projections about global warming impacts playing out in 2015.
"There had been projections of the dying of coral reefs worldwide. They are becoming true now. You know the science, you trust the science, but to see this actually happening, it's an interesting experience. If you look at the graphs, it shows that, at 1 degree of global warming, the death curve for corals is taking off. At 1.5 degrees, they're practically all gone, and we're right at that point," he said.