A new analysis of the extraordinary heat that affected the Arctic in 2016 finds that it could not have happened without the steep increases in greenhouse gas concentrations caused by human activity, and resulting loss of sea ice, over the past 150 years.

Evaluating ocean and atmospheric observations with advanced modeling tools, scientists from NOAA and CIRES found that about 60 percent of 2016’s record warmth was caused by record-low sea ice observed that year, and the ensuing transfer of ocean heat to the atmosphere across wide expanses of ice-free or barely frozen Arctic Ocean.

However, Arctic sea ice loss alone was insufficient to explain the totality of record warmth, the researchers said. Influences from outside the Arctic, such as the 2015-16 El Niño and remarkable intrusions of warm air that originated from outside the Arctic Circle, were also factors causing the 2016 extreme warmth.

The research team concluded that there was near-zero probability that the Arctic would be as warm as it was in 2016 if greenhouse gas concentrations, ocean temperatures, and sea ice were at late 19th Century levels. The new research appears online in the journal Weather and Climate Extremes.

CIRES' Lantao Sun, who works in the NOAA Earth System Research Laboratories, is the lead author on this study.

This story was adapted from NOAA Research communications.