Global Climate Change

Global Climate Change Introduction Global climate change is a change in the long-term weather patterns that characterize the regions of the world. The term "weather" refers to the short-term (daily) changes in temperature, wind, and/or precipitation of a region. Weather is influenced by the sun. The sun heats the earth's atmosphere and its surface causing air and water to move around the planet. The result can be as simple as a slight breeze or as complex as the formation of a tornado. Some of the sun's incoming long wave radiation is reflected back to space by aerosols. Aerosols are very small particles of dust, water vapor, and chemicals in Earth's atmosphere. In addition, some of the sun's energy that has entered Earth's atmosphere is reflected into space by the planet's surface. The reflectivity of Earth's surface is called albedo. Both of these reflective processes have a cooling affect on the planet. The greenhouse effect is a warming process that balances Earth's cooling processes. During this process, sunlight passes through Earth's atmosphere as short-wave radiation. Some of the radiation is absorbed by the planet's surface. As Earth's surface is heated, it emits long wave radiation toward the atmosphere. In the atmosphere, some of the long wave radiation is absorbed by certain gases called greenhouse gases. Greenhouse gases include carbon dioxide (CO2), Chlorofluorocarbons (CFC's), methane (CH4), nitrous oxide (N20), tropospheric ozone (O3), and water vapor. Each molecule of greenhouse gas becomes energized by the long wave radiation. The energized molecules of gas then emit heat energy in all directions. By emitting heat energy toward Earth, greenhouse gases increase Earth's temperature. While greenhouse gases absorb long wave radiation then emit heat energy in all directions, greenhouse walls physically trap heat inside of greenhouses and prevent it from escaping to the atmosphere.

The greenhouse effect is a natural occurrence that maintains Earth's average temperature at approximately 60 degrees Fahrenheit. The greenhouse effect is a necessary phenomenon that keeps all Earth's heat from escaping to the outer atmosphere. Without the greenhouse effect, temperatures on Earth would be much lower than they are now, and the existence of life on this planet would not be possible. However, too many greenhouse gases in Earth's atmosphere could increase the greenhouse effect. This could result in an increase in mean global temperatures as well as changes in precipitation patterns. When weather patterns for an area change in one direction over long periods of time, they can result in a net climate change for that area. The key concept in climate change is time. Natural changes in climate usually occur over; that is to say they occur over such long periods of time that they are often not noticed within several human lifetimes. This gradual nature of the changes in climate enables the plants, animals, and microorganisms on earth to evolve and adapt to the new temperatures, precipitation patterns, etc.

The real threat of climate change lies in how rapidly the change occurs. For example, over the past 130 years, the 7mean global temperature appears to have risen 0.6 to 1.2 degrees Fahrenheit (0.3 to 0.7 degrees Celsius). The increasing steepness of the curve suggests that changes in mean global temperature have occurred at greater rates over time. Further evidence suggests that future increases in mean global temperature may occur at a rate of 0.4 degrees Fahrenheit (0.2 degrees Celsius) each decade. The geological record--the physical evidence of the results of processes that have occurred on Earth since it was formed--provides evidence of climate changes similar in magnitude to those in the above graph. This means during the history of the earth, there have been changes in global temperatures similar in size to these changes. However, the past changes occurred at much slower rates, and thus they were spread out over long periods of time. The slow rate of change allowed most species enough time

to adapt to the new climate. The current and predicted rates of temperature change, on the other hand, may be harmful to ecosystems. This is because these rates of temperature change are much faster than those of Earth's past. Many species of plants, animals, and microorganisms may not have enough time to adapt to the new climate. These organisms may become extinct.

Role of oceans Oceans affect climate in many ways. As the major reservoir of water, oceans dominate the movement of water, supplying most of the water vapour in the atmosphere by evaporation. Of this evaporated water, 91 percent is returned to the oceans as precipitation; the remainder is transported and precipitated over landmasses. Runoff and groundwater from land flow back to the oceans. The oceans and the atmosphere are tightly linked, and together form the most dynamic component of the earth’s climate system. They bring moisture to coastal areas that may be carried inland by the wind. Typhoons and hurricanes form over the oceans, and as oceans get warmer these will be more frequent. Most of the incoming solar radiation is received in tropical regions while very little is received in Polar Regions especially during winter months. Over time, energy absorbed near the equator spreads to the colder regions of the globe, carried by winds in the atmosphere and by currents in the ocean. Compared to the atmosphere, the ocean is much denser and has a much greater ability to store heat. The ocean also moves much more slowly than the atmosphere. Thus, the ocean and the atmosphere interact on different time scales. The ocean moderates seasonal and longer variations by storing and transporting, via ocean currents, large amounts of heat around the globe, eventually resulting in changing weather patterns. Winds and currents are constantly moving the ocean’s waters. Surface currents flowing north or south transport heat, and carry warmed or cooled water several thousand kilometers, thereby ameliorating the extremes of heat or cold. Deep ocean currents also flow across the globe. The Gulf Stream Drift, for example, is powered by cold, dense, salt-laden water sinking off the north polar coastal regions and moving south in the depths, pushing the surface warm water from the tropical and subtropical Atlantic (including some from the Gulf of Mexico) up north to bathe the shores of Western Europe, producing a climate that is surprisingly mild for that latitude. Global warming and melting of the polar icecaps freshens the surface water, reducing its density and preventing it from sinking. As a

result, the Gulf Stream slows down, or may even reverse; bringing severe winters to northern Europe while the rest of the earth heats up. In places where cold deep waters come up to the surface, as near San Francisco in California USA, the climate is as cool as Dublin in Ireland 1600 km further north.

The global atmosphere and world oceans are an interactive system. The most important air-sea interaction signal comes from the El Niño/Southern Oscillation (ENSO) which originates in the tropical Pacific. In a warm episode (El Niño), the pool of warm water that is normally found in the western Pacific expands eastward, carrying with it portions of the precipitation normally found in the far western Pacific. This shift in the distribution of tropical convection leads to shifts in jet stream tracks, resulting in climatic anomalies around the world. The ENSO cycle is rooted in the instability of the coupled atmosphere ocean system and occurs over an irregular, quasiperiodic cycle which varies between three and seven years.

The ocean also plays an important role in climate change. Long-term impacts of climate change in coastal areas, such as sea level rise or storm surges, could result in the increased erosion of shores and associated habitat, increased salinity of estuaries and freshwater aquifers, altered tidal ranges in rivers and bays, changes in sediment and nutrient transport, and increased coastal flooding.

Rising sea level increases the salinity of both surface water and ground water through salt water intrusion. Some cities like New York City, obtain their water from portions of rivers that are slightly upstream from the point where water is salty during droughts. If sea level rise pushes salty water upstream, then the existing water intakes might draw on salty water during dry periods. Salinity increases in estuaries also can harm aquatic plants and animals that do not tolerate high salinity. Shallow coastal aquifers are also at risk. The freshwater Everglades currently recharge Florida's Biscayne aquifer, the primary water supply to the Florida Keys. As rising water levels submerge low-lying portions of the Everglades, portions of the aquifer would become saline.

Polar Regions include the Arctic in the Northern Hemisphere and Antarctica in the Southern Hemisphere. The Arctic is expected to experience the greatest rates of warming compared with other world regions. In part, this is because ice has greater reflectivity (also known as albedo) than the ocean or land. Melting of highly reflective snow and ice reveals darker land and ocean surfaces, increasing absorption of the sun's heat and further warming the planet, especially in those regions. There is evidence that climate change is already having observable impacts in the Arctic and in Antarctica. Many of these observed changes are consistent with the expected effects of climate change under a range of climate scenarios.

Like the Arctic in the Northern Hemisphere, Antarctica in the Southern Hemisphere has been experiencing effects attributable to changes in regional climate. Future changes resulting from global climate change are also expected to be significant in this region of the world. Over the past half-century, there has been a marked warming trend in the Antarctic Peninsula. Much of the rest of Antarctica has cooled during the last 30 years, due to ozone depletion and other factors, but this trend is likely to reverse. Surface waters of the Southern Ocean surrounding Antarctica have warmed and become less saline, and precipitation in this region has increased. Antarctica has experienced significant retreat and collapse of ice shelves, the result of regional warming. The loss of these ice shelves has few direct impacts on sea level and global climate. Because the ice shelves were floating, their melting does not directly add to sea level rise. They usually are replaced by sea-ice cover, so overall albedo (reflectivity) changes very little. Satellite observations show no significant change in Antarctic sea-ice extent over the 1973-2005 period. Analysis of whaling records and modeling studies provide some evidence for longer-term declines in sea ice extent in some regions, but there are not enough data to provide firm conclusions. As climate change continues, most of the land-based Antarctic ice sheet is actually likely to thicken if projected warming increases snowfall. There is a small risk, however, that the West Antarctic ice sheet will retreat in coming centuries. This is because the West Antarctic ice sheet is moored in an oceanic basin, where slippery mud covers the basin floor. This unique setting makes the ice sheet potentially unstable.

Effects on Biological and Human Systems •

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Arctic impacts will have implications for biodiversity around the world because migratory species depend on breeding and feeding grounds in the Arctic. Reduced sea ice is likely to increase marine access to the region’s resources, expanding opportunities for shipping and possibly for offshore oil extraction (although operations could be hampered initially by increasing movement of sea ice in some areas). As frozen ground thaws, many existing buildings, roads, pipelines, airports, and industrial facilities are likely to be destabilized. Increased areas of tree growth in the Arctic could serve to take up carbon dioxide (CO2, the principal greenhouse gas emitted by human activities) and supply more wood products and related employment, providing local and global benefits. However, tree growth would mean absorption of additional sunlight (as the land surface would become darker and less reflective) and add to regional warming.

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Climate change is taking place within the context of many other ongoing changes in the Arctic, including observed increases in chemical contaminants entering the Arctic from other regions, over fishing, land use changes that result in habitat destruction and fragmentation, rapid growth in the human population, and cultural, governance and economic changes.