Global climate patterns have undergone a remarkable shift in the past 600,000 to 1.2 million years. Before the transition, glacial cycles, consisting of cold ice ages and milder interludes, typically lasted about 40,000 years—but those weaker cycles gave way to longer-lasting icy eras with cycles lasting roughly 100,000 years. In between the cold ice ages are periods of thawing and warming known as interglacial periods, during which sea levels rise and ice retreats. Here Past Interglacials Working Group of PAGES identifies and compares interglacial periods over the past 800,000 years, including our current era.
Glacial periods give way to interglacials on some occasions when the Northern Hemisphere’s summer solar insolation (the amount of solar radiation received by Earth’s surface) increases alongside corresponding decreases in ice volume and increases in temperature and atmospheric carbon dioxide (CO2). Although the end of an interglacial period is a slow process requiring the sequential reversal of these conditions, the onset of an interglacial period can be relatively fast. Within the glacial periods, there are secondary fluctuations. These are known as interstadial and stadial periods, which occur when glaciers retreat and advance, respectively.
Despite the occurrence of interstadials and stadials, the researchers evaluated the overall strength of interglacials. In total, the researchers identified 11 different interglacials during the study period. In addition, using sea surface temperature and other data, they found that two interglacial periods in particular—marine isotopic stage (MIS) 5 and MIS 11–were particularly strong almost everywhere.
Although most interglacials typically last about 10,000 to 30,000 years, the researchers suggest that the current epoch—the Holocene—may last much longer because of the increased levels of atmospheric greenhouse gases resulting from human activity. The authors predict that this current interglacial period won’t give way to a glacial period for another 50,000 years or so. The only way the current interglacial could end earlier is if CO2 levels were reduced to well below preindustrial levels. (Reviews of Geophysics, doi:10.1002/2015RG000482, 2015)
—Cody Sullivan, Writer Intern
Citation: Sullivan, C. (2016), Characterizing interglacial periods over the past 800,000 years, Eos, 97, doi:10.1029/2016EO047001. Published on 2 March 2016.