Key Facts About Arctic Sea Ice

By Dr. Flavio Lehner



23 Jun 2023

Arctic Sea Ice Day is coming soon, July 15th, and once again, we’re drawing attention to this remarkable frozen ocean ecosystem, the ice loss taking place, and how a shift to renewable energy can help reverse that trend.

As part of our countdown to the day, our chief climate  scientist, Dr. Flavio Lehner, shares nine key facts about Arctic sea ice.

1. Sea ice is to the Arctic ecosystem as soil is to the forest.

When ocean water gets cold enough to freeze it expels its salt, causing channels to form in the ice. Algae grow within these channels and form the base of the food chain. Algae feed the tiny organisms, like zooplankton, that inhabit these waters. Arctic cod feed on them. Seals eat Arctic cod. And polar bears prey on seals.

A polar bear stands on an ice floe in the sea

Photo: Dick and Val Beck

2. Polar bears rely on sea ice to efficiently catch their main prey, ice seals.

Although seals can out-swim polar bears underwater, bears have the edge on top of the ice, using it to sneak up on and stalk their next meal. Ice seals, and related ice-dependent species like the walrus, rely on sea ice for survival, too—they use it to rest on and as a platform for giving birth to and raising their pups. 

A seal resting on an ice floe.

Photo: KT Miller

3. Arctic sea ice is important to people living in the North, providing a platform for transportation and increased access to food.

But people around the world need sea ice too. Sea ice acts like a global air conditioner, helping to cool the planet by reflecting the sun's light and heat back into space rather than absorbing it into the water.

Overhead view of fragmented sea ice.

Photo: BJ Kirschhoffer

4. Less sea ice = extra heat absorbed into the ocean = less heat reflected away from Earth = disrupted climates.

Just as a heart circulates blood and regulates the body’s temperature, the ocean controls the world’s climate system by circulating heat, moisture, and nutrients around the planet. Disruptions in this system, such as extra heat, have global impacts and can lead to changes in weather patterns and destruction of marine ecosystems.

Overview of Arctic waters with melting sea ice.

Photo: KT Miller

5. Arctic sea ice is declining in both extent and thickness due to human-caused climate warming.

The atmosphere is like a blanket that surrounds the earth. When we burn fossil fuels like coal, oil, and gas for energy, we release extra carbon emissions into our atmosphere. This buildup thickens this “blanket,” trapping in more heat around our earth, raising our average global temperature and disrupting the climate.  Just as a warm summer's day melts the ice in a glass of water, a warming planet causes Arctic sea ice to melt.

A polar bear on melting sea ice.

Photo: KT Miller

6. Some sea ice still remains in the Arctic year-round, with the lowest extent occurring each summer in September.

Despite year-to-year variation, satellite data show that the rate of sea ice decline for September sea ice is 82,300 square kilometers (32,000 square miles) per year, or 12.8 percent per decade compared to the 1981 to 2010 average. That’s like losing an area the size of South Carolina or New Brunswick every year.

Bird's eye view of melting sea ice.

7. A new study shows that, without action to reduce heat-trapping emissions, Arctic open-water periods are projected to lengthen dramatically by 2100.

Longer open-water periods in summer would greatly reduce the polar bear’s ability to hunt during these months, impact ice seal abundance, and affect people and wildlife around the world. Furthermore, it is possible that the rapidly-warming Arctic and ice free oceans can amplify extreme weather events that then adversely impact agriculture, infrastructure, economics, and human lives around the world.

Walruses resting on a small ice floe.

8. Data shows we have entered a new era with sea ice.

Today, there is more thin, seasonal ice in some parts of the Arctic compared to the thick, multi-year ice that used to be more common. This young ice is much more vulnerable to rapid melting and moves more easily, resulting in a treadmill-like effect for polar bears trying to find their next meal or mate. This causes the bears to burn more energy to find food, which has consequences for their health and, eventually, population-level impacts.

A polar bear walking on a band of sea ice with a towering glacier in the background.

9. The last 16 years have had the lowest 16 sea ice extents in the satellite record, according to NASA and the National Snow and Ice Data Center. The amount of old, thick sea ice is the lowest it has ever been.

Despite the threats, it’s important to remember that it's not too late to save Arctic sea ice. Studies show there is no tipping point. The ice will rebound if we work together now to shift away from fossil fuels, replacing them with renewable energy sources like solar and wind. Not only will this help reduce the carbon emissions that are causing the planet to warm and the sea ice to melt, it will also create jobs, strengthen the economy, and improve the overall environment and our health.

Visit our Arctic Sea Ice Day page to learn how you can join us in celebrating sea ice and helping to safeguard its future. 

Dr. Flavio Lehner is the chief climate scientist for Polar Bears International and assistant professor in Earth and Atmospheric Sciences at Cornell University.

A small band of sea ice curves into open ocean waters.