What is the Cryosphere?
The cryosphere influences our world's climate, contributes to sea level rise, provides water resources for ecosystems, and is central to the daily lives of the people, plants, and animals that have made it their home.
As part of the global climate system, snow and ice cool the planet by reflecting solar energy from their white surface back into space. Earth’s atmosphere, ocean, and landscapes are intricately connected to the cryosphere, affecting circulation, precipitation, waterways, mountain range erosion, and vast areas of the northern continents. Moisture transfers between frozen water and the atmosphere influence cloud cover formation, precipitation, and atmospheric circulation. Water composition, such as fresh meltwater flowing into a salty ocean, strongly affects ocean circulation. These back-and-forth exchanges influence long-term trends in climate and regional weather patterns.
Sea level rise occurs in one of two ways: when water temperatures increase, or when meltwater from snow or ice flows into the ocean. When water heats up, the space between molecules expands. So, when the ocean warms, sea level rises. About one-third of sea level rise is from thermal expansion of the ocean. When ice on land melts and its water runs into the ocean, or when a solid mass of ice like an iceberg plunges into the sea, sea level also rises. In total, snow and ice account for only about 2 percent of all water on Earth, but about 69 percent of total fresh water on Earth is stored in ice caps and glaciers.
Glaciers, seasonal snowfall, and ice play an important role in storing the planet’s freshwater reserves. For example, the Asian mountain ranges surrounding the Tibetan Plateau, like the Himalaya and Hindu Kush, hold the world's largest reservoir of perennial glaciers and snow outside of the polar ice sheet. Each spring, rivers bulge with meltwater from snow and ice, delivering fresh water to over one billion people for drinking, agriculture, and hydropower. In areas like the Rocky Mountains of North America, seasonal snow helps sustain the Colorado River Basin, which delivers water to farms, cities, and ecosystems in much of the US Southwest.
As greenhouse gas levels continue to increase in the atmosphere, global temperatures continue to rise. Since it only takes a slight uptick in temperature to go from frozen to thawed, the polar regions are especially sensitive to climate change. Data show that the Arctic is warming at two to three times the rate of the rest of the planet. A warmer planet thaws snow and ice faster and earlier in spring, exposing darker oceans and land. These dark surfaces then absorb more solar radiation, intensifying the impacts of climate change.
Where is the cryosphere?
The polar regions, the Arctic, and Antarctic, bookend the cryosphere, but it extends to vast areas in between.
The Arctic, where the North Pole lies, is largely an ocean basin surrounded by land. It includes the vast Arctic Ocean, adjacent seas, and parts of Alaska, Canada, Greenland, Iceland, Norway, Sweden, Finland, and Russia. Frozen ground and permafrost ring the Arctic Ocean, where sea ice expands in the fall and winter and shrinks in the spring and summer. On the floor of the Arctic Ocean lies undersea permafrost.
The Greenland Ice Sheet, second in size to the Antarctic Ice Sheet, covers about 80 percent of Greenland, the world's largest island.
At the other end of Earth, surrounding the South Pole, lies a massive icy landmass—Antarctica. The Antarctic Ice Sheet covers about 13.7 million square kilometers (5.3 million square miles) or 98 percent of the continent. It is the largest block of ice on Earth. Antarctica is one of two ice sheets, Greenland being the other. Antarctica is a polar desert, and the coldest, driest, and windiest continent. In some places, plates of thick floating ice extend into the ocean called ice shelves. The outer sections of these ice shelves periodically break off, or calve, and form icebergs. The icebergs float in the oceans, melting and falling apart as they drift into warmer waters.
And in between
The cryosphere also exists in places between the poles, especially at high elevations. For example, glaciers and snow cover Mount Kilimanjaro in Tanzania, a mountain lying about 3 degrees (about 322 kilometers or 200 miles) south of the equator. The Asian mountain ranges surrounding the Tibetan Plateau, like the Himalaya and Hindu Kush, are known as Earth’s third pole because of the number of perennial glaciers and amount of snow found there.
About a quarter of the Northern Hemisphere’s land is permafrost, where the ground is frozen for at least two years. Nearly 85 percent of Alaska sits atop a layer of permafrost. It is also widespread in the Arctic regions of Siberia, Canada, and Greenland and found in high-altitude regions like the Rocky Mountains, Tibetan Plateau, South American Andes, and New Zealand’s Southern Alps.
Glaciers are found in mountain ranges on every continent, except for Australia. Glaciers, including alpine glaciers, ice caps, and ice sheets, cover about 10 percent of the planet, providing drinking water to billions of people. Melting glacial waters also swell rivers for irrigation, hydropower, agriculture, and recreation.
The cryosphere expands seasonally in places where snow falls and freezing temperatures cause the soil, rivers, lakes, and ocean to freeze.
How is the cryosphere changing?
The cryospheric regions, or regions where water is found in solid form, provide us with direct visual evidence of global temperature changes. Unlike other substances found on Earth, ice and snow exist relatively close to their melting point. Water changing from solid to liquid and back often results in dramatic visual changes across the landscape as various snow and ice masses shrink or grow. Examples of these changes can be seen from the Arctic to Antarctica and nearly everywhere in between.
The cryosphere is an especially sensitive indicator to climate change. Consequently, consistent and prolonged warming trends have resulted in observable changes to Earth's cryosphere. A study published in 2021 made a global estimate, for the first time, quantifying the extent by which sea ice, snow cover, and frozen ground cover Earth. The researchers then compared how climate change has impacted that extent. Between 1979 and 2016, Earth has lost 87,000 square kilometers (33,000 square miles), an area about the size of Lake Superior, per year on average. The extent of the cryosphere matters because its bright white surface reflects sunlight, cooling the planet. Changes in the area and location of snow and ice can alter air temperatures, change sea levels, and even affect ocean currents worldwide.
In the Arctic
Scientists first began noticing changes in the Arctic in the 1980s, but it was not yet clear then if the response was a warming trend or natural variability. By the mid-1990s, however, it became clear that the rapid warming of the Arctic is a signal of human-caused climate change. Since 1990, the Arctic has warmed at roughly twice the rate as the entire globe, a phenomenon known as Arctic amplification. Several factors may be contributing to the Arctic’s extreme warming:
- The region’s reflectivity, or albedo—how much light it bounces back into space—is decreasing with sea ice loss. When white snow covers sea ice, which is often, it reflects about 90 percent of the sun’s energy, keeping the surrounding atmosphere cooler. Bare sea ice, by contrast, reflects between 50 and 70 percent of solar radiation. However, sea ice still reflects much more of the sun’s rays than the ocean, keeping the environment cooler than it would be without ice.
- The ocean’s darker surface reflects less than 10 percent of the sun’s heat. This means that it absorbs about 90 percent of solar energy, warming the surrounding atmosphere and increasing nearby land temperatures. For sea ice to form, the ocean must cool enough to freeze. With higher ocean temperatures at the end of summer, it is taking longer for sea ice to form in the fall.
- Changes in ocean currents are another factor. Water enters the Arctic Ocean from both the Pacific and Atlantic, with much larger inflow from the Atlantic side. The Atlantic Ocean is saltier, and thus denser, than the Arctic Ocean. Denser water sinks. So, the Atlantic Ocean typically sinks below the Arctic Ocean surface and away from sea ice. Higher temperatures, however, are pulling Atlantic water closer to the surface, where it can potentially melt sea ice.
- Sea ice decline also exposes surface waters to more wind, which mixes up colder fresh water at the surface with warmer salt water below, raising the ocean’s surface temperatures and melting more sea ice. Data also show larger inflows from the Pacific Ocean, warming the Arctic Ocean and increasing sea ice melt.
Arctic amplification is not the only evidence of rapid climate change in the Arctic. The floating sea ice cover of the Arctic Ocean is shrinking, especially during summer. Snow cover over land in the Arctic has decreased, notably in spring, and glaciers in Alaska, Greenland, and northern Canada are retreating. According to the 2020 Arctic Report Card, rising surface temperatures have fueled bigger fires in high latitudes of the Northern Hemisphere since the 1980s. In addition, permafrost in many parts of the Arctic is warming and thawing.
Scientists have already seen evidence of positive feedbacks of warming in the Arctic. As permafrost thaws, once frozen plants and animals begin to decay. As they decay, they release carbon dioxide and methane back into the atmosphere, further contributing to warming. According to the 2019 Arctic Report Card, permafrost thaw throughout the Arctic may be releasing an estimated 300 to 600 million tons of net carbon per year to Earth's atmosphere.
The changing vegetation of the Arctic also affects the surface brightness, which then influences warming. As the Arctic atmosphere warms, it can hold more water vapor, which is an important greenhouse gas. The loss of ice mass from the Greenland Ice Sheet is increasing to such an extent that sea level rise forecasts have had to be adjusted.
There are also negative feedbacks in the Arctic. For instance, higher temperatures may allow for a longer Arctic growing season, allowing plants to grow longer and take up more carbon from the air. However, most evidence suggests that the positive feedback effects outweigh the negative feedbacks.
Outside of the Arctic, the Antarctic Peninsula, a swirly tail of mountains that stretches out from the continent, is one of the fastest warming areas on Earth. Antarctica is covered by an ice sheet roughly the size of the United States and Mexico combined. The ice sheet is responding to climate change in a variety of ways.
The Transantarctic Mountains divide Antarctica into two sections: East and West Antarctica—indicating regions that lie mostly in the Eastern or Western Hemisphere, respectively. Though research has shown that climate change has impacted both sides, the West Antarctic Ice Sheet (WAIS) is of particular concern because its underlying bedrock rests far below sea level. As stated earlier, ice shelves buttress the continental ice sheet, putting the brakes on glacial flow into the oceans. Warming ocean waters are cutting under the floating ice shelves and eroding the point of its connection to land. Coupled with higher air temperatures, the ice shelves could rapidly crumble. Since much of the WAIS bedrock is well below sea level, as the ice sheet begins to retreat and thin, a large portion of the ice sheet may lift off the bedrock and float. The floating ice provides less resistance to flow, and the large ice mass will slide faster into the ocean, causing further thinning, retreat, and flotation—a potentially runaway process that could increase sea level at several times the current rate.
Antarctica contains more than half of the world's fresh water in its sprawling, ice sheet. If the WAIS portion crumbled into the ocean, it would raise sea levels by 3.5 meters (12 feet) and affect ocean currents as it flushed fresh water into the briny ocean. It should also be pointed out that when sea levels rise, they do not rise uniformly: winds and Earth’s gravity distribute water unevenly. Some coastal areas will be inundated by higher-than-average sea level increases, while others less so.