According to a study under the guidance of Rutgers University, the main mystery behind climate change has been resolved by the researchers, which shows that the current yearly global temperature is the warmest of the last 10,000 years—in contrast to recent research.
The study has been published in the journal Nature.
The long-term mystery is known as the “Holocene temperature conundrum,” with few skeptics claiming that climate model forecasts of future warming must be incorrect. The researchers add that their results will contradict the long-held opinions on the temperature history in the Holocene era, which started around 12,000 years ago.
Our reconstruction shows that the first half of the Holocene was colder than in industrial times due to the cooling effects of remnant ice sheets from the previous glacial period –contrary to previous reconstructions of global temperatures. The late Holocene warming was indeed caused by the increase in greenhouse gases, as predicted by climate models, and that eliminates any doubts about the key role of carbon dioxide in global warming.
Samantha Bova, Study Lead Author, Rutgers University–New Brunswick
Bova is also a postdoctoral researcher associate in the lab of co-author Yair Rosenthal, a Distinguished Professor in the Department of Marine and Coastal Sciences and Department of Earth and Planetary Sciences at Rutgers University.
Researchers made use of the marine calcareous (calcium carbonate-containing) fossils from foraminifers—single-celled organisms found at the surface of the ocean—to rebuild the temperature histories of the two latest warm intervals on Earth. They are the Holocene and the Last Interglacial period from 128,000 to 115,000 years ago.
The researchers obtained the fossils by gathering a core of bottom sediments in the vicinity of the mouth of the Sepik River off northern Papua New Guinea at the time of the Rutgers-led Expedition 363 of the International Ocean Discovery Program.
The core includes quickly piling up sediments that enabled the researchers to rebuild the temperature history of the western Pacific warm pool, which carefully tracks variations in global temperatures.
The evolution of temperature during the Last Interglacial and Holocene eras is questionable. Certain data indicate that the average annual global temperature during the modern era does not surpass the warmth in the early warm period of the Holocene, known as the “Holocene thermal maximum,” following which global cooling occurred. At the same time, climate models strongly indicate that global temperatures have increased across the last 1000 decades.
The apparent discrepancy between climate models and data has cast doubts among skeptics about the role of greenhouse gases in climate change during the Holocene and possibly in the future.
Yair Rosenthal, Study Co-Author and Distinguished Professor, Department of Marine and Coastal Sciences and Department of Earth and Planetary Sciences, Rutgers University–New Brunswick
“We found that post-industrial warming has indeed accelerated the long and steady trend of warming throughout the past 10,000 years. Our study also underscores the importance of seasonal changes, specifically Northern Hemisphere summers, in driving many climate systems. Our method can, for the first time, use seasonal temperatures to come up with annual averages,” added Rosenthal.
The co-authors of the study affiliated to Rutgers University are Shital P. Godad, a former Rutgers researcher currently working at National Taiwan University. Researchers from The Ohio State University and Nanjing Normal University were also part of the study.
Bova, S., et al. (2021) Seasonal origin of the thermal maxima at the Holocene and the last interglacial. Nature. doi.org/10.1038/s41586-020-03155-x.