A 19th-century polar explorer depicted the harrows of traversing the Arctic, "for its course is tracked with hardships, and its field is sown with graves."
The often-frigid, ice-clad Arctic remains a harsh world. But in the early 1900s, there was substantially more ice than there is today. New research used old shipping logs, meticulously kept by mariners often each hour, to extend the Arctic sea ice record back 110 years, over seven decades before satellites began regularly monitoring the high north.
Back then, sea ice showed a lot of variability, with an overall decline between 1901 through 1940. But that decline pales when compared with the Arctic's plummeting sea ice thickness and extent over the last four decades.
"There is nothing even remotely like [the last 40 years]," noted Axel Schweiger, a sea ice scientist at the University of Washington and a lead author of the research.
The Arctic is the fastest warming region on Earth. The 12 lowest sea ice extents in the satellite record have all happened the last 12 years. This year, sea ice has either been at record lows or been flirting with record lows all summer.
"The differences between the two periods are stark," said Walt Meier, a senior research scientist at the National Snow and Ice Data Center, who had no role in the study.
"I think this paper really provides solid evidence that the current sea ice decline is decidedly different -- both in scale and nature -- than the decline earlier in the 20th century," Meier added.
In the early 1900s, U.S. mariners logged their location using a navigational instrument called a sextant, and regularly documented sea ice encounters with notes like "steering various courses and speeds" (to avoid collisions). The logbooks, kept at the National Archives in Washington, D.C., were transcribed and digitized by citizen scientists, making the data available for research.
"The current rate of sea ice decline is unprecedented since at least the early 20th century."
"This is a very valuable contribution to our understanding of Arctic sea ice variability since the early 20th century," said Zack Labe, a climate scientist and PhD candidate at the University of California. "The UW study adds to the growing body of evidence that the current rate of sea ice decline is unprecedented since at least the early 20th century."
In this study, Schweiger and his team employed the old mariner logs to verify their past reconstruction of Arctic sea ice volume, based on past climate conditions on both sea and land. Without the old logs, the researchers couldn't have validated their models of sea ice extent and thickness going back over a century -- before the first aircraft ever took flight. "The model we checked against the logs is quite good," explained Schweiger.
"Based on the limited sea ice data available and temperatures [at the time], I’d say their reconstruction is quite reasonable," noted Meier.
Although the 1920s through the 1940s were a warm period on Earth, the warming wasn't all over the Arctic like it is today -- so there was significantly less of a sea ice decline back then.
"The current warming and ice loss is over the entire Arctic and throughout the year, so there is a much bigger effect," Meier said.
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It's almost certain that Arctic mariners a century ago experienced an Arctic that was vastly different than it is today. Their logbooks paint a picture of sea ice that fluctuated year-to-year -- as it does still -- but there was not a such a deep, long-term, downward trend in sea ice extent.
That's a consequence of Earth's skyrocketing carbon emissions, which are now at their highest levels in at least 800,000 years -- though likely millions of years.
