Vital Arctic sea ice shrank to tie its lowest level measured for winter, the ice-growing season, as a warming Earth broke records on every continent.
Arctic sea ice levels, especially in summer, are crucial to Earth’s climate because without ice reflecting sunlight, more heat energy ends up in the oceans. Ice of all types around the poles acts as the Earth’s refrigerator. Wildlife, such as polar bears and seals, also depend on sea ice. The lack of sea ice in the Arctic creates new shipping routes and, in doing so, causes geopolitical disruptions, making previously ignored places, such as Greenland, more desirable.
The decline in Arctic sea ice was announced Thursday as temperatures broke record heat in March across the United States, all of Mexico, Australia, North Africa and parts of northern Europe. Climatologist and weather historian Maximiliano Herrera, who tracks extreme temperatures, called March’s temperature extremes “by far the most extreme heat event in global climate history” and said on social media that the coming days would be “much worse.”
Sixteen states broke March temperature records over the past week, weather historian Christ Burt said. According to meteorologists, temperatures high enough to equal or exceed the hottest April day ever recorded were recorded in 27 locations last week, including San Luis. Thousands of records have been shattered in Mexico, some of them warmer than the highest temperatures in May, but that is nothing compared to what is happening in Asia, where “tens of thousands of monthly records” were shattered with margins of 30 to 35 degrees (17 to 19 degrees Celsius), Herrera said.
However, earlier this week, Antarctica set the record for the coldest day in March anywhere on Earth, at 105.5 degrees below zero (76.4 degrees Celsius below zero), according to Herrera and Burt.
Steady decline in sea ice
Each year, Arctic sea ice grows during the cold winter and shrinks in the heat of summer. This year the growth has been so small that its peak, before it began to shrink, measured 5.52 million square miles (14.29 million square kilometers). This figure is slightly less than last year’s 14.31 million square kilometers, but the National Snow and Ice Data Center, which makes the measurements, considers the two figures to be so close that it is a tie.
This year’s sea ice area was about 525,000 square miles (1.36 million square kilometers) lower than the average winter peak from 1981 to 2010. That’s about twice the size of Texas.
“As temperatures have warmed and continue to warm, especially in the polar region, there is less opportunity for ice to grow and it is going to tend to be, on average, smaller,” said data center principal scientist Walt Meier. “It’s not that we’re seeing a regime change or anything like that. It’s more of a steady decline in winter and at the maximum. And it also gives us an advantage in the summer melt season. We’re starting from a lower number.”
Sea ice in summer is key
The summer melting season, which precedes the September measurement known as the Arctic sea ice minimum, is “really the critical time,” Meier says. One reason is that when there is less white ice to reflect the strong summer sun, the oceans can absorb more heat. And when that happens, the Arctic warms closer to temperatures further south and atmospheric pressure changes. One of the main theories – still controversial – states that these changes in the Arctic alter the movement and shape of the jet stream, which shifts time from west to east and contributes to extreme weather explosions.
Melting sea ice does not contribute to sea level rise.
The winter sea ice growing season is also more variable with weather changes, so just because the Arctic reached a small record amount in March doesn’t mean the summer will be a record one, Meier said.
“The winter high is certainly interesting,” Meier said. “It is, I would say, a sign of global warming due to climate change.”
At the other end of the planet, Antarctic sea ice is greatly affected by local meteorological and oceanic factors. In February, Antarctica hit its annual low, and while it was lower than the 30-year average, it was nowhere near the record lows of the last three years, according to Meier.