Arctic Matters: The Global Connection to Changes in the Arctic (2015)

The Arctic

Dispatches from the Front Lines of Climate Change

By definition, global climate change is reflected in a host of changes all over the planet. But changes do not occur uniformly across the globe. Changes in the Arctic have been generally more rapid than those anywhere else on Earth. Strange sights — such as forests of “drunken trees” loosened by thawing permafrost — provide dramatic visual evidence of this rapid change (Figure 1).

FIGURE 1. This forest of “drunken trees” in Alaska is a clear sign of thawing permafrost. When permafrost thaws it can make the ground buckle, causing trees to lose their footing and tip over at odd angles. Source: National Snow and Ice Data Center, University of Colorado, Boulder/Tingjun Zhang

TEMPERATURES ARE RISING.

Temperatures are rising twice as fast in the Arctic as compared to the average global temperature rise (Figure 2). The most dramatic manifestation of this warming is seen during the Arctic winters, which are becoming milder. The temperature of the Arctic Ocean is also increasing, a pattern that is exacerbated as sea ice melts, leaving more of the water’s surface exposed and allowing more heat to be taken up by the open water during the summer months.

FIGURE 2. Temperatures have risen faster in the Arctic than elsewhere on the globe. This map depicts the temperature trend from 1950 to 2014. This analysis was assembled using publicly available data from roughly 6,300 meteorological stations around the world; ship-based and satellite observations of sea surface temperature; and Antarctic research station measurements. Source: NASA Earth Observatory/ NASA Goddard Institute for Space Studies (GISS)/ Kevin Ward

SEA ICE IS MELTING.

If you were to stand at the North Pole, the snow and ice under your boots would feel rock-solid, and its white expanse might extend as far as you could see. But you would not be standing on land, because Earth’s North Pole is in the middle of the Arctic Ocean. You would be standing on sea ice — ice floating on the ocean’s surface.

Each summer, as temperatures rise above freezing, the ice begins to melt and the area covered by sea ice shrinks (Figure 3). In winter, sea ice coverage expands again as sea water freezes.

But over the past several decades, warmer temperatures have meant there is less sea ice left at the end of the summer. Using satellites, scientists have found that the area of sea ice coverage each September has declined by more than 40 percent since the late 1970s, a trend that has accelerated since 2007.

In fact, by the end of each of the eight summers from 2007–2014, Arctic sea ice extended over less area than at any time in the preceding three decades — the time period for which we have satellite observations. In 2012, the ice shrank to its smallest extent ever recorded by satellites, with the ice covering only half the area covered just 30 years earlier.

This striking decrease in summer ice has also caused winter ice to become thinner and less stable. Even a few decades ago, a large core of sea ice survived the summer and beyond, thickening and hardening over many winters to become multiyear ice (generally 3–4 meters [10–13 feet] thick). But now, more summer melting means an increasing fraction of winter sea ice cover is first-year sea ice (generally only 1–2 meters [3–7 feet] thick) that melts more quickly and breaks up more easily in the summer, contributing to the overall trend of sea ice loss (Figure 4).

FIGURE 3. These images of Alaska’s Bristol Bay, taken by the Moderate Resolution Imaging Spectroradiometer (MODIS) on the NASA Aqua satellite, illustrate the thinning and thawing of arctic sea ice each spring. The image on the left was taken on April 11 2012, and shows sea ice hugging the shore. Two weeks later, on April 24, the ice had retreated (right). Source: NASA Earth Observatory/ Jesse Allen

FIGURE 4. The extent of multi-year ice is decreasing rapidly. These visualizations show sea ice coverage in 1980 (left) and 2012 (right). Multi-year ice is shown in bright white, while younger sea ice is shown in light blue to milky white. The data show the ice cover for the period of November 1 through January 31 in their respective years. Source: NASA Earth Observatory

LAND ICE IS MELTING.

Ice is melting at a rapid pace on the land masses that encircle the Arctic Ocean.

Glaciers, many of which have endured since the last Ice Age or longer, are becoming smaller (Figure 5). Those that border bodies of water are increasingly breaking off into icebergs, a process called calving. The icebergs then float away and gradually melt into the sea.

The Greenland ice sheet is essentially an enormous glacier that extends about 1,699,000 square kilometers (656,000 square miles) and covers most of the island of Greenland. In recent decades, this ice sheet has begun to decrease in size and mass as a result of warmer summer temperatures melting ice at the surface, and increased calving of ice at the island’s edges.

Snow cover has also decreased as temperatures rise and snow melts off more quickly in the spring and summer. For example, snow cover in June 2012 was 40 percent below the average from 1971–2000 — the baseline period of observations — in many areas of the Arctic.

This loss of ice from Arctic land masses contributes to sea level rise, alters the way water moves over and through the land, and could affect the circulation of the oceans and atmosphere globally.

FIGURE 5. Recent losses of land ice are illustrated by comparing a 1976 photograph of Muir Glacier in Glacier Bay National Park and Preserve, Alaska (left) with a 2003 photograph of the same glacier (right). The 1976 photograph shows the calving edge of Muir Glacier (where icebergs break off) extending the width of the fiord, and aside from algae growing on a lighter colored dike, there is no vegetation visible in the photograph. The 2003 photograph documents the disappearance of Muir Glacier from the field of view, and shows vegetation beginning to develop. Source: USGS/Bruce F. Molnia.

PERMAFROST IS THAWING.

Although permafrost derives its name from the word “permanent,” it is becoming markedly less so.

Defined as soil, rock, and any other subsurface earth material that exists at or below freezing for two or more consecutive years, permafrost thaws when ground temperatures increase. Permafrost ranges from solid to sporadic, depending on temperature and soil type. Discontinuous (patchy) permafrost is particularly susceptible to thawing. Scientists have seen declines in permafrost over the past 30 years and predict that discontinuous permafrost will likely disappear across much of the Arctic, where ground temperatures are now within 1–2° C (1.8–3.6° F) of thawing.

The effects of changes in permafrost are complex because each area has a unique geological, chemical, atmospheric, and biological environment. When permafrost thaws, it can have significant impacts on an area’s landscape, ecosystem, hydrology, and infrastructure, for example by causing the collapse of roads, bridges, runways and buildings (Figure 6).

FIGURE 6. Ocean waves erode coastlines the world over, but in parts of Alaska coastal erosion has accelerated due to two climate-driven phenomena: declining sea ice and thawing permafrost. Arctic sea ice absorbs wave energy, dampening the waves that beat against the shoreline, but declines in summertime sea ice cover are creating expanses of open ocean that allow storms to stir up waves. At the same time, thawing permafrost means that land is becoming softer and more vulnerable to erosion. Taken near Drew Point, along Alaska’s northern coast, the photo on the left shows how ocean waves have undercut the land nearest the shore. The photo on the right, taken about a year later, shows chunks of coastline tumbling into the sea. Source: Stratus Consulting/University of Colorado; NOAA Climate.gov

ARCTIC ECOSYSTEMS ARE CHANGING.

The Arctic is home to living creatures found nowhere else on Earth. Many are highly specialized, having evolved in response to the unique Arctic environment over millions of years. As ice melts and temperatures change, these species face mounting challenges — including the possibility of extinction.

Some of the most recognizable Arctic animals, such as polar bears, seals, and walruses, rely on sea ice as a platform for resting and hunting. Like the Arctic’s human residents, these animals face the loss of habitat and drastically reduced hunting ranges as sea ice recedes.

For example, in past years walruses in the Chukchi Sea (between Alaska and the Russian Far East) would have been found scattered across a large area of sea ice overhanging the shallow waters of the continental shelf, using the ice as a resting platform between dives to forage for clams and worms in the seabed. In recent years, however, that sea ice has largely been confined to the deeper waters of the far north, forcing tens of thousands of walruses to come ashore in Alaska and Russia (Figure 7). From land, the walruses must travel farther to reach their prey, forcing them to expend extra energy and making them more vulnerable to illness, competition, and trampling.

FIGURE 7. In September 2014, an estimated 35,000 walrus came ashore in Point Lay, Alaska. Source: NOAA
INSET: A female walrus and pup rest on an ice floe. Source: U.S. Geological Survey/Sarah Sonsthagen

As the Arctic grows more temperate, some species are seizing the opportunity to expand into new territory. The melting of sea ice has created new expanses of open ocean, allowing large populations of phytoplankton to bloom and causing shifts in the marine food chain. On land, shrubs are expanding in the tundra and invasive insects are sweeping across the forests (Figure 8). As Arctic summers warm and the ice-free season lengthens, more species from the south could begin to spread northward. Competition from these species for food and other resources could potentially lead to major ecosystem reorganization and even extinctions.

Arctic ecologists are particularly concerned about “tipping points” — thresholds where a small change in climate could have major, irreversible ecological impacts. Scientists are investigating how to predict tipping points in the hope of developing strategies to minimize their impacts. The 2011 National Research Council report Frontiers in Understanding Climate Change and Polar Ecosystems identifies key research questions to better understand the ecological impacts of climate change in the Arctic.

As climate warms, shrubs have started to grow in areas previously dominated by tundra vegetation such as lichens, an important winter food source for caribou. The loss of lichens can lead to declines in the growth and abundance of caribou, which in turn, are an important food source for hunters from the Arctic’s indigenous communities as well as for predators such as bears and wolves. Source: U.S. Fish and Wildlife Service/Dean Biggins

FIGURE 8. As temperatures have risen in the Arctic, the growing season has got longer in the far northern latitudes, bringing major changes to Arctic ecosystems. Instruments on NASA and NOAA satellites have continuously monitored the growth of vegetation from space since the late 1970s. Scientists use that information to calculate the Normalized Difference Vegetation Index (NDVI), an indicator of photosynthetic activity, or the “greenness” of the landscape. These maps show NDVI trends between July 1982 and December 2011 for the northern portions of North America and Eurasia. Shades of green depict areas where plant productivity and abundance increased; shades of brown show where photosynthetic activity declined. There was no significant trend in areas that are white, and areas that are gray were not included in the study. The maps show a ring of greening in the treeless tundra ecosystems of the circumpolar Arctic — the northernmost parts of Canada, Russia, and Scandinavia. Tall shrubs and trees started to grow in areas that were previously dominated by tundra grasses. The researchers concluded that plant growth had increased by 7 to 10 percent overall. Source: NASA Earth Observatory

LIFE IS CHANGING FOR THE PEOPLE OF THE ARCTIC.

The Arctic is home to about 4 million people. They range from city dwellers to oil prospectors to hunters and herders living on the land. Many are members of indigenous groups whose ancestors have lived in the Arctic for millennia. They are citizens of eight different countries who speak dozens of distinct languages.

These unique and diverse Arctic communities face an uncertain future. Thawing permafrost poses particularly significant problems. As permafrost thaws, the shape of the land changes and streams or bodies of water can form in areas that were previously dry. Resulting erosion wreaks havoc on buildings, roads, pipes, and other infrastructure, costing communities hundreds of millions of dollars as they struggle to make repairs and keep up with changing conditions.

Towns situated along the coasts are especially vulnerable. Historically, large swaths of sea ice forming along the shoreline have provided a buffer against coastal storms and waves. As sea ice declines, coastal communities face the full brunt of increasingly strong storms. In addition, sea-level rise threatens low-lying communities, and advancing seas and stronger storms may force some communities to relocate.

The 2014 National Research Council report The Arctic in the Anthropocene: Emerging Research Questions explores the need for actionable Arctic science to better understand how environmental and societal changes will affect the Arctic and the rest of the world.