Global Climate Change Explorer: Ice

Turn up the heat, and ice will melt. The effect of climate change on the world’s ice is almost that simple. Global temperatures are warming, and that warming is fastest at the poles. As a result, ice sheets and glaciers melt and shrink.

So while there's still lots of snow and ice in the polar regions, there’s much less of it than there used to be.

Credit: NOAA

Antarctica's Ross Ice Shelf at the Bay of Whales.

The Problem with Melting

Melting ice is bad news for several reasons:

Meltwater from the ice sheets and glaciers flows into the ocean, causing sea levels to rise. This can lead to flooding, habitat destruction, and other problems.
Ice reflects the Sun’s energy better than than land or water. So with less ice, Earth absorbs more energy, and heats up faster.
Many animal species rely on icy habitats to survive—polar bears, seals, foxes, wolves, and many others are threatened by global melting.

Secrets in the Ice

Ice also holds secrets about Earth’s climate history. By drilling into Antarctica’s ice sheets and extracting ancient layers, scientists can measure what the climate was like over the last 800,000 years.

Dataset 1
Today’s Arctic Sea Ice Report

White areas below show how much of the Arctic is currently covered by sea ice. The ice naturally grows and shrinks every winter and summer (March has the most ice; September the least.)

Based on microwave data gathered via satellite, this image shows how much of the Arctic Ocean is currently covered by ice at more than 15% concentration. Source: National Snow and Ice Data Center, University of Colorado Boulder

Slowly Shrinking

The orange line shows the normal (median) ice coverage for that day, based on measurements from 1981–2010. Because of rising temperatures due to climate change, you'll usually see less ice than the normal line.

Arctic sea ice coverage is shrinking by 3% or more per decade. And some climate models suggest that if CO₂ emissions continue to rise, the Arctic Ocean could be nearly ice-free by 2050.

Ice levels grow and shrink in a regular cycle each year, but the current year’s ice curve on this graph is usually well below the gray median, or normal, line for 1981–2010. See an interactive sea ice graph from the National Snow and Ice Data Center. Source: National Snow and Ice Data Center

Less Ice Means More Warming

Ice reflects sunlight; you know this if you’ve ever squinted against the blinding glare of sunlight on snow. (Scientists call this reflectivity albedo.)

Without ice cover, land or ocean water reflects much less sunlight. And when the Sun's energy isn't reflected, it gets absorbed, causing the ocean or land to heat up. So the more ice melts, the more sunlight the planet absorbs, and faster it warms.

When sunlight hits sea ice, about 90% of the light energy gets reflected back toward the atmosphere. But ice-free ocean water reflects only 6%, and absorbs the other 94% of the energy as heat. Read more about albedo.

Sea Ice versus Land Ice

In one respect, melting sea ice isn’t as bad as melting ice on the land. That’s because sea ice floats, and like melting ice cubes in a cold beverage, it doesn’t raise sea level when it melts.

Ice Balloon

To learn more about ice, freezing and melting try the Ice Balloons Science Snack.

More Sites about Arctic Sea Ice

Dataset 2
Today’s Antarctic Sea Ice Report

The white area surrounding Antarctica shows how much of the ocean is currently covered by sea ice. The ice naturally grows and shrinks every winter and summer (September has the most ice; February, the least.)

The orange line shows the normal (median) ice coverage for that day, based on measurements from 1981–2010.

Based on microwave data gathered via satellite, this image shows the extent of the Southern Ocean around Antarctica that’s currently covered by ice at greater than 15% concentration. Source: National Snow and Ice Data Center, University of Colorado Boulder

The Opposite of Melting

In spite of climate change, Antarctic sea ice has been growing by about 1.8% per decade. Scientists aren’t sure why, but they think it may be caused by the frigid ocean current that surrounds Antarctica, and by the continent’s icy winds.

Sea Ice Growing, Land Ice Shrinking

Though Antarctic sea ice is growing, the ice sheets on the continent itself are shrinking—by an estimated 219 billion metric tons per year, as of 2018. This melting appears to be accelerating, and is contributing to sea level rise.

The Antarctic ice sheet has lost more than 1,000 gigatonnes of ice since 2002, according to ice mass measurements from NASA’s GRACE satellites.

Dataset 3
A Frozen History of the Climate

The multicolored line in this graph shows the carbon dioxide (CO₂) levels in Earth’s atmosphere, measured in ice core samples from Antarctica. It goes from 800,000 years ago to about 1978.

Almost all of these CO₂ measurements were taken from ice cores collected in Antarctica, and published by scientists working with NOAA’s National Climate Data Center. Source: Based on NOAA Carbon Dioxide Pumphandle video

They Call this Graph the Hockey Stick

Over hundreds of thousands of years, Earth's CO₂ levels rose and fell, but they never got above 300 parts per million—until the late 1800s. That’s when humans began generating CO₂ by burning more and more fossil fuels for energy. After 1850, the line rises so fast that it looks almost vertical.

This clearly shows that CO₂ levels are much higher today than at any time in the last 800,000 years. And direct CO ₂ measurements reveal that it’s still rising higher every year.

How Does Ice Tell Us the Climate’s History?

Antarctica’s ice sheets formed very slowly over thousands of years, as each year’s snowfall became compacted into solid layers of ice. When each new ice layer formed, it trapped tiny bubbles of air—like bottled samples of the atmosphere from that time. By drilling down into these ice sheets, scientists can measure the gases that were in Earth’s atmosphere many centuries ago.

Credit: NASA

As Antarctic snow builds up over many years, the layers underneath become harder and more dense.

Credit: Oregon State University

The bubbles in this ice from an Antarctic ice core contain carbon dioxide and other gases, trapped thousands of years ago when the ice formed. Researchers carefully crush the ice and capture the gases that escape to measure the CO₂ levels.

Evidence of Ice Ages

While past CO₂ levels don’t tell us how warm the climate was, other trapped gases can. Data from oxygen and other gases show that ice ages happen when CO₂ levels are low, warmer periods happen when CO₂ levels are high.

Vostok Petitgraph

Scientists measured the relative amounts of different oxygen and hydrogen isotopes in the ice core samples; these isotopes vary with temperature. These two graphs show that high temperatures happened when there was more heat-trapping CO₂ in the atmosphere. Source: Based on graph from Wikimedia Commons, original data from Petit, et al, 1999

More Sites about Ice Core Data

Dataset 4
As Glaciers Melt, Sea Levels Rise

The yellow line rising from left to right shows the total sea level rise caused by melting glaciers from 1961 to 2003.

Total sea level rise from melting glaciers

The total sea level rise from glacier melting were calculated from a global database of glaciers and their mass change over time. Source: Based on graph from National Snow and Ice Data Center

Sea Level Rise: A Game of Inches

The total amount of sea level rise from glacier melt—about 2 centimeters (0.75 inches)—might sound small, but even a couple of inches causes increased flooding in coastal regions like the Bay Area. As glaciers melt faster, the yellow line is getting steeper—sea level rise is accelerating.

Going, Going...

Glaciers naturally fluctuate over time. They advance in colder years, and retreat in warmer years. But in recent decades many glaciers have retreated to a stunning extent.

Credit: National Snow and Ice Data Center

Muir Glacier, Glacier Bay, Alaska in 1941, 1976, and 2004.

Credit: USGS

McCarty Glacier, Kenai Fjords National Park, Alaska in 1909 and 2004.

Credit: Lonnie G. Thompson

The retreat of Qori Kalis Glacier in Peru between 1976 and 2004 left behind a large lake.

Earth’s Huge Ice Sheets Are Shrinking Too

Glaciers are relatively small ice masses, but Earth also has two gigantic ice sheets. They cover the majority of Greenland and Antarctica. Both of these ice sheets have been losing mass since 2002, and that melt is accelerating. Like the melting glaciers, that’s causing sea levels to rise.

The Greenland ice sheet has lost more than 3,500 gigatonnes of ice since 2002, according to ice mass measurements from NASA’s GRACE satellites. Source: NASA

More Sites About Glaciers and Ice Sheets

Exploratorium Ice Stories: Traversing the Antarctic Ice Sheet
Exploratorium Ice Stories: Measuring a Glacier’s Motion
Fluctuations of Glaciers Browser
Cryosphere and Sea Level Rise: From the National Snow and Ice Data Center

Dataset 5
Case Study: The Breakup of Larsen B Ice Shelf

These satellite images from January to April 2002, show the collapse of the Larsen B Ice Shelf on the Antarctic Peninsula.

Credit: NASA

On January 31, the ice shelf (left) is dotted with blue pools of meltwater, forming lines above crevasses in the ice. A smattering of icebergs appears in the dark, open waters.

Credit: NASA

By February 17, the shelf begins to splinter. The leading edge has retreated about 10 kilometers (6 miles).

Credit: NASA

By February 23, several more long, narrow icebergs have broken away.

Credit: NASA

By March 7, the shelf has disintegrated, filling the bay with a mixture of slush and icebergs. Many of the bergs have toppled over, exposing the very pure blue ice from the bottom of the shelf.

By April 13, the bright blue color has faded as the first snows of the season cover the icebergs. Thinner seasonal ice begins to form, locking most of the ice debris in place for the winter. View slideshow at NASA's Earth Observatory. Source: NASA’s Earth Observatory at Goddard Space Flight Center

The following summer, when the seasonal ice melted, the icebergs began drifting away with the currents. And during many summers since then, the bay has been completely ice-free.

Missing: The Larsen Ice Shelves

The collapsed part of the Larsen B Ice Shelf was larger than the state of Rhode Island. It was the largest in a series of retreats of the Larsen Ice Shelf.

Larsen A Ice Shelf, just to the north, collapsed abruptly in 1995. Smaller sections of Larsen B broke away between 1998 and 2002. And Larsen C Ice Shelf lost the second largest single iceberg ever recorded in 2017.

Map of Antarctic Ice Shelves

Antarctica has numerous ice shelves. Those on the Antarctic Peninsula have been shrinking in recent years. Source: Based on maps from NASA.

The Antarctic Peninsula, where the Larsen Ice Shelf is located, has warmed more than the rest of the continent. And scientists believe the collapse of the Larsen B Ice Shelf was at least partly caused by warming temperatures. The rest of Antarctica is cooling, and its largest ice shelves are gaining mass. For example, the Ross Ice Shelf (south of New Zealand) is thickening as the glacier streams connected to it slow down.

What Is an Ice Shelf, Anyway?

An ice shelf is a thick plate of ice that extends out over the surface of the ocean, and is connected to an ice sheet (land ice) at the shoreline.

Ice Sheet and Shelf Anatomy

Because an ice shelf is already floating, its disintegration doesn’t immediately make sea levels rise. But an intact ice shelf pushes back against the ice sheet or glacier behind it on the land. So when the shelf collapses, the ice sheet flows and melts much faster (though still at a glacial pace) into the ocean. And melting ice sheets do increase sea levels.