Polar bears are on the move. The area of arctic sea ice on which these carnivores hunt seals has declined 34 percent as worldwide temperatures rise. As this ice is lost, polar bears must swim as far as 100 kilometers (about 60 mi) to find their prey. Some of these polar bears cannot make it, and they drown. Now polar bears must compete with grizzly bears. If climate change is changing the shape of one of Earth’s coldest regions, how will it affect the rest of our planet?
Ecosystems at Risk
In the 20th century, the average global temperature rose by 0.6ºC (1ºF). The difference may seem small, but it is an average for the entire globe. Near the poles, the effects of climate change are more dramatic. Since 1949, average annual temperatures in Alaska have risen 1.8ºC (3ºF)—enough to lengthen the summer melting season for sea ice and glaciers. From 1979 to 2007, Arctic sea ice retreated enough to expose an additional one million square miles of open water—the equivalent of six Californias.
Good and Bad News?
In the rest of the world, the impact of climate change on Earth’s species may be mixed. Many animal species, such as birds and butterflies, can move to cooler areas as the climate warms. But insects and microorganisms that cause infectious diseases, such as malaria and yellow fever, are also spreading toward the poles. Some plant species cannot move as quickly as the climate is expected to change, and may become extinct.
Researchers are also finding that changing temperatures can affect animals in surprising ways. The sex of some reptiles, for example, is partially determined by the temperature of the developing egg. A consistent warming trend could cause some reptiles to become extinct by creating entire generations that are all the same sex. Migratory birds and marine mammals also face challenges. For example, birds that wait until their normal migration time to fly north in the spring may arrive too late, missing the best weeks for laying eggs and catching the insects they need to raise their young. In addition, some researchers have predicted that the productivity of phytoplankton, the algae on which ocean food webs are based, may decline in some areas. A change of this sort could cause a domino effect in marine food webs. If phytoplankton levels decline, fish will have less food and will be less numerous. If fish are less numerous, marine mammals and birds will have less to eat too. In addition, studies show that this increase in global temperatures is linked to a four percent increase in ocean humidity and a six to eight percent increase in rainfall, leading to stronger hurricanes.
But the news may not be all bad. Some of the same research shows that the same factors that increase the strength of a hurricane also make it less likely that the hurricane will ever make landfall. The retreat of Arctic sea ice may someday make it possible to open a shipping lane through the Arctic Ocean. Scientists theorize that climate change has been accelerated by increased levels of carbon dioxide in the atmosphere. Many plants, including crops such as cotton, soybeans, wheat, and rice, can benefit from the increase in CO2. They can absorb the CO2 and yield more at harvest time as a result. On the other hand, in warmer weather crops may also be more at risk from insect pests and from severe storms or droughts.
Scientists have little doubt that Earth’s climate is changing. It is impossible to predict exactly how any ecosystem will be affected by climate change. However, biologists and climatologists are collecting data about processes including solar radiation, precipitation, evaporation, the transfer of heat energy by winds and by ocean currents, and the ways in which plants affect climate. They interpret this information using computer models and try to answer questions about how global warming will affect Earth.
- Could climate change alter certain ocean currents, changing Earth’s temperatures further?
- How quickly might the polar ice caps melt?
- How have global climate changes affected Earth’s ecosystems in the past?
- Is there a way to preserve biodiversity on mountain tops and polar areas where animals and plants have no cooler places to migrate to?
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Deep Sea Sediment Coring
Analyzing ocean floor sediments can provide scientists with data about how plants and animals were affected during past climate changes. The process of collecting deep sea sediments is expensive and time-consuming, but the results of this research give scientists a look at what life in the oceans was like millions of years ago.
To study these ancient organisms, scientists need sediment samples that are hundreds of meters long. To obtain these, they must use drills similar to the drills used by the oil and gas industry. Taking these samples requires many hours and can be dangerous if the seas are rough or full of ice. Once scientists have obtained the cores, they first split the core in half lengthwise. One half is sampled for fossils of ancient organisms. This is the “working half.” The other half, the “archive half,” is saved and stored away so that future scientists who may develop other questions can have access to this difficult-to-obtain material.
By carefully dissecting the working half of the sample, scientists discover microscopic fossils of marine animals. Scientists know that these ancient animals were very sensitive to slight changes in temperature and chemistry. These microfossils can tell scientists how Earth’s climate has changed over millions of years.
Oceanographer in Action
For Ruth Curry, spending time on the ocean waves has nothing to do with surfing or vacationing. She spends her time studying the ocean currents that affect our lives each day. Ruth Curry is an oceanographer at the Woods Hole Oceanographic Institute, an organization of scientists who research and study how the ocean affects the global environment.
Curry’s research focuses on the North Atlantic circulation and the currents that carry warm waters from tropical regions northward. As these warm waters reach higher latitudes, they release heat that warms the air above them and warms the climate of western Europe. As warm water cools, its density increases and it sinks to the bottom of the ocean. There it begins a southward journey back to the tropics. This conveyor belt of water plays an important role in maintaining Earth’s climate. Normally, the salinity, or saltiness, of ocean water stays about the same. But changes in global temperatures are melting large sheets of ice in Greenland, which is introducing large amounts of fresh water into the ocean. This fresh water is diluting the ocean water, making it less salty. A decrease in salinity makes ocean waters less dense and prevents them from sinking to the bottom of the ocean. Eventually, the melting of ice sheets in Greenland could cause the North Atlantic currents to slow and eventually stop, leading to dramatic changes in the Northern Hemisphere’s climate.