Glacial Retreat and Biodiversity

Alaskan glacier

Glacial retreat, a consequence of climate change, may have a large impact on biodiversity. (Photo credit: Digital Vision/Getty Images)

As a result of climate change, glaciers around the world are melting. What impact might this have on biodiversity?

A glacier is a body of ice made from compacted fallen snow that persists over many years. Glaciers occur at the north and south poles, but also in more temperate areas, including in mountains at the equator. They can be as small as a football field, or many kilometers long. Glaciers move, but due to their very large mass, they travel at a very slow rate. Glaciers are sensitive to even small changes in temperature, and so they are good indicators of climate change.

Many glaciers are found in the Arctic, where the temperature increases due to climate change have been felt the most so far. Already, some glaciers have disappeared worldwide and many are retreating so quickly they may disappear within the next 30-50 years. Glaciers at lower elevations are generally retreating the most quickly, but even some large glaciers at high elevations are shrinking. Most scientists link the burning of fossil fuels, such as coal and oil, in manufacturing and electricity production are driving climate change and glacial retreat. The Industrial Revolution has caused a dramatic increase in carbon dioxide and other greenhouse gases that trap heat within Earth’s atmosphere. It is not just the atmospheric gases that cause a problem. Black particles of soot that land on glaciers reduce the reflectivity of the ice and speed glacial melt even more.

At first thought, a warming planet might seem beneficial for Earth’s inhabitants. After all, biodiversity is often richest in Earth’s warmest places. But species can take thousands of years to adapt to changed conditions, and a new equilibrium means extinction for many existing species. The Earth cycles through Ice Ages and warm periods naturally. The last ice age, called the Little Ice Age, ended around the year 1850. It is not the fact that Earth is warming that is so alarming to most scientists, but the rate that it is doing so. Glacial retreat has increased in most areas of Earth rapidly since the late 1900s. Most famously affected are polar bears in the Arctic. Loss of sea ice has affected polar bears’ ability to hunt their preferred food, seals. Reduced nutrition means reduced body size and reduced reproduction rates. Polar bears are a highly visible example of the effects of glacial retreat, but scientists also worry about the effect of glacial retreat on much smaller animals.

Macroinvertebrates, or insect larvae, live within the sediments of streams. One study has looked at macroinvertebrates living in streams fed by glacier meltwater in the Alps, Alaska, and Andes mountains. These areas represent temperate, arctic, and tropical glacial regions. The small organisms in the study, which include mayflies (Ephemeroptera), caddis flies (Trichoptera), and true flies (Diptera), are often used as indicators of an aquatic ecosystem’s health. Scientists have recently projected that when glaciers have melted back to expose 30– 50 percent of their drainage basins, some species of macroinvertebrates will disappear. Water flow increases and decreases with change in glacier size, and as the glaciers retreat, sediment flow into the streams changes too. Some rocks and sediment are released from the glacial ice itself, and glacier movement also disturbs and moves underlying soil. If the glaciers completely melt, diversity of macroinvertebrates may decrease almost 40 percent. side from being indicators of water quality, macroinvertebrates have several important roles in ecology. They are decomposers, which means they break down once-living material into the smaller components that make up soil. They are also an important part of aquatic food chains. If the macroinvertebrates disappear, the effects would undoubtedly be felt at higher trophic levels, including among fish, amphibian, bird, and mammal species.

One of the main reasons that glacial retreat affects biodiversity is because many species that live in such specialized environments are found nowhere else on Earth. Species unique to a region are called endemic species. Small numbers of individuals that once moved northward toward mountain glaciers may have become geographically isolated. A small group of individuals have a small amount of genetic variation, and as they breed over many generations, a new species can develop. In extreme environments, these new populations have developed specific adaptations to survive. These advantages they may have in cold temperatures and harsh conditions can become disadvantages when the climate warms, even just a few degrees. One researcher, by reviewing more than 800 scientific studies on the subject, has found that extinctions are already happening in fragile habitats due to human-induced global temperature increases. Extinctions of specialized species will continue as long as temperatures continue to rise. Antarctica, with its large number of endemic species, is a region of major concern. The Arctic, where recorded temperature changes have been the largest, is another. The Himalayan mountain range also has many glaciers and over three thousand endemic plant species, as well as already threatened bird, mammal, and amphibian species. While insects and other short-lived species have shown evidence of evolving, it is not at a rate that would ensure their future survival. Many other species, such as Emperor penguin colonies and red fox populations, have changed their distributions due to global warming, moving pole-ward as temperatures warm and glaciers retreat. Smaller habitat is a threat to biodiversity.

Glaciers worldwide have responded to climate change in different degrees. Scientists are just beginning to get a clear picture of changes that have already occurred and those that are projected to occur in our near future. But the vast majority of studies have shown the importance of decreasing greenhouse gas emissions and the need to develop technologies that reduce atmospheric carbon. Earth’s biodiversity is already being threatened, and that is just one of many concerns that glacial retreat raises for Earth’s many inhabitants.

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