Most people view our planet’s vanishing ice as a symptom of climate change. And if they pay a bit more attention, some people might even be aware of some of its effects, including sea level rise and the opening up of the Arctic to shipping. But ice is also an active player in the Earth's climate—it doesn’t only respond to warming by melting. Changes in our planet’s ice are capable of feeding back on the climate system, creating further consequences for the globe.

The regions of our planet where temperatures fall below the freezing point are characterized by ice and snow, lots of ice and snow. Across land masses, seas, and oceans, roughly 70 percent of the fresh water exists as ice. But now, in response to the warming of our planet, that entire system is changing.

This part of the Earth, where water exists in its frozen state, is called the cryosphere. On land, this includes the giant ice sheets on Greenland and Antarctica, the ice in mountain glaciers, snow on mountain tops, and frozen soil in boreal and tundra regions of the Northern Hemisphere—including large parts of Canada and Russia. The system is dynamic. In the world's polar regions, sea ice grows in winter and recedes in summer. On land there are also frozen rivers and lakes, which can also experience seasonal variation. The cryosphere is the global story of ice, and it’s a highly active and important component in our Earth's climate system.

But, again, the behavior of the cryosphere is changing. That is primarily because ice responds to rising temperatures, melting with increasing heat. For example, shelf ice, which floats on the oceans near ice sheets, can weaken in response to the warming water below, causing destabilization and collapse. In the Arctic, sea ice is vanishing in the summers, changing the way in which the ocean absorbs sunlight. Across the continents, mountain glaciers and the ice sheets of Greenland and Antarctica are melting. Cryosphere changes like these are having profound impacts on our planet.

Albedo feedbacks

Albedo is a measure of how reflective a surface is, and the Earth's albedo influences the climate by determining how much sunlight is absorbed. Ice and snow have very high albedos, meaning they reflect a lot of sunlight. According to Dr. Johannes Sutter, a climatologist at the Alfred Wegener Institute in Bremerhaven, Germany, “the cryosphere is the planet's air conditioner. Its white surface—snow and ice—reflect much of the incoming sunlight, cooling the environment.”

Thus, changes in ice coverage can modulate the temperatures of nearby regions. This is especially true with respect to sea ice, which is currently undergoing a massive decline in the Arctic. These areas are experiencing a phenomenon known as polar amplification, warming at a much higher rate than the rest of the planet.

“By mid-century, the Arctic ocean could be ice free in summer,” says Sutter. “That accelerates warming even further by exposing the darker ocean surface. It's like choosing between sitting in a black or a white car on a hot summer’s day.” Darker surfaces absorb more heat; and exposed ocean surfaces do exactly that.

This change in albedo is known as a climate feedback, with decreases in albedo acting on the local climate and causing increasing temperatures. On a societal and economic level, reduced sea-ice in the Arctic also means the opening up of new shipping routes and opportunities for oil exploration, both of which would again ultimately contribute to the amplification of global warming.

“Another factor with regard to albedo effects is black carbon, which is a major component of soot,” says Sutter. Black carbon is deposited on the Greenland ice sheet either by natural or human sources, such as wildfires or combustion, These deposits could lead to decreasing the albedo of the ice sheet, further increasing regional temperatures. “These dark particles might form a blanket that could further accelerate Greenland ice mass loss,” he says.

Ice sheets and sea levels

Most of the ice on Earth is stored in the ice sheets on Greenland and Antarctica. In fact, about 99 percent of freshwater ice on the planet is locked up in these regions. The Greenland and Antarctica ice sheets are massive mounds of ice that reach heights of up to 4,500 meters and extend across solid bedrock for many thousands of miles. Think about that—it’s almost three miles of ice. This means there's a lot of ice that could melt as the atmosphere warms up. As meltwater runs off into the oceans, sea levels across the globe will rise, posing a threat to humanity, especially those living in large coastal cities.

Dr. Sutter has spent the past six years researching how the cryosphere works. His work has focused predominantly on Antarctica, which he visited on a 2013 expedition as part of his PhD research. He has also spent time on Svalbard, the Norwegian island in the Arctic.

“At the moment Greenland is definitely the elephant in the room when it comes to sea level rise,” he says. “Between 2005 and 2010, its sea level contribution was almost twice as big as Antarctica’s.”

This is partly because the Arctic is a global warming hotspot due to polar amplification, and it’s experiencing much more warming compared to the global average. “In summer, the ice melts on Greenland's surface, forming rivers that transport the melt water to the ocean, thereby raising sea levels,” he says.

While Greenland is the bigger problem now, Antarctica is much bigger and has more ice. Long term, it has much more potential for affecting global sea level. According to Sutter, “if you look at a business-as-usual climate scenario, a destabilized Antarctic ice sheet could raise sea levels by more than a meter by the end of the century.”

“In Antarctica the situation is different from that on Greenland,” he continued. “Being much colder than Greenland all year round and currently shielded from the effects of global warming due to its unique setting—being surrounded completely by the large Southern Ocean. Its major contribution to sea level rise comes from marine glaciers flowing into the ocean, such as the Thwaites and Pine Island Glaciers.”

Those Antarctic glaciers are currently stabilized by large ice shelves along the coast, which keep the glaciers in place and prevent significant sea-level rise. But it now appears that these ice shelves are shrinking due to both the warming of the oceans below and the air above.

If the shelves go, the glaciers could accelerate, dumping their contents into the oceans and draining the ice sheets behind them. “If this trend continues, whole regions of the West Antarctic Ice Sheet could be destabilized, leading to rising sea levels worldwide,” Sutter says.