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How much has Arctic ice declined, and how does that compare to past periods in the Earth's history?

Over the last 40 years, annual Arctic sea ice measurements show ice shrinking by 12.6 percent each decade, a pace of decline that’s unmatched by any point in at least the last 1,500 years.

April 10, 2023

Scientists measure Arctic sea ice every year in September, when satellite imaging shows ice coverage at its lowest. Since 1979, when the U.S. government started taking those measurements, Arctic ice has declined by more than 2 million square kilometers.1
“It’s a pretty large chunk of ice that is lost,” says Gianluca Meneghello, a research scientist who focuses on Arctic oceanography in MIT’s department of Earth, Atmospheric and Planetary Sciences. “It’s one of the strongest signals of climate change.”
Satellite measurements are the preferred method of monitoring Arctic sea ice, because pictures taken from space can most accurately capture the size of Arctic sea ice cover and its constant fluctuations. In September of 2022, satellite data showed ice covering 4.67 million square kilometers of the Arctic Ocean, an area more than 11 times the land area of California.
But scientists have a few ways to measure changing sea ice levels from long before the invention of satellites. Data on Arctic ice prior to the late 1970s comes from geologic information stored in sediments, the presence of microfossils and their chemical composition. Additionally, small gas bubbles or fossils trapped in old ice in glaciers, and even the different hydrogen and oxygen isotopes that make up the ice itself, can reveal clues about past states of the atmosphere or the Earth’s temperature. Climatologists can use that data to estimate past ice levels.
Arctic ice fluctuates a lot over geologic time, and there have been periodic examples of a completely ice-free Arctic over the last 350,000 years. But at least some amount of year-round Arctic ice cover developed around 5,000 years ago and has been with us ever since. The spread of today’s Arctic ice is not only small compared to earlier points in human history—it’s also shrinking faster than at any point in at least the last 1,500 years, the period for which we have the most detailed data on historical ice cover.2 Based on current climate models, scientists expect that Arctic ice will disappear completely over the summer in the coming decades.3
This loss of ice is important in part because it creates a feedback loop that causes further warming. The pale color of ice reflects more than 80 percent of light that hits it back into space, deflecting warming from the Earth’s surface. But when ice melts, light instead hits the darker seawater below it, which reflects only about 10 percent of sunlight. The ocean absorbs the rest.
“If you remove ice, there’s more light hitting the ocean and the ocean is warming up,” says Meneghello. “So during the next winter it’s more difficult to form ice.”
The Arctic, says Meneghello, is like an ice factory. The ice produced there, when the atmosphere is cold enough, helps modulate temperatures in other parts of the world. In a world without ice, that won’t happen. Temperatures will rise, as will sea levels.
“The Arctic has changed a lot over long timescales,” says Meneghello. “It doesn’t mean that the the most recent changes are good for us.”


Thank you to Donald Lee Runkle of West Bloomfield, Michigan, for the question. You can submit your own question to Ask MIT Climate here.

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1 NASA: Vital Signs of the Planet: Arctic Sea Ice. Accessed April 10, 2023.

2 National Oceanic and Atmospheric Administration: "Paleoceanographic Perspectives on Arctic Ocean Change." December 4, 2017.

3 International Cryosphere Climate Initiative: "State of the Cryosphere Report 2022." November 2022.