The Earth’s climate is controlled through a complex set of environmental and astronomical interactions. As radiant energy from the Sun reaches the Earth, some of it is reflected directly back into space by clouds and ice coverage. Much of this energy, however, is absorbed by exposed land and water, and is then reradiated into the atmosphere within the infrared spectrum, i.e. heat. Differential heating produces wind patterns, which in turn drive our weather systems. Certain gases in the lower atmosphere, such as water vapor, carbon dioxide (CO2), methane (CH4), chlorofluorocarbons (CFCs), and others, trap some of this heat before it escapes completely back into space. The effect of these gases is analogous to glass windows surrounding a greenhouse, and is in fact often referred to as the Greenhouse Effect. This trapped heat is necessary to keep the Earth’s climate warm enough for life to exist. There must, therefore, be some kind of a balance to insure the Earth neither cools nor warms too much.
The Earth's gaseous envelope today consists almost entirely of nitrogen (N2) and Oxygen (O2). Together, these two gases compose about 97% of the atmosphere, but it also contains many other essential gases in small amounts. Various of these gases, primarily water vapor (including clouds), carbon dioxide (CO2), and methane (CH4), are known as greenhouse gases, because they entrap heat within the biosphere which forms when sunlight is absorbed by the Earth's surface and reradiated as heat. If it were not for the greenhouse gases, the overall temperature of the Earth would be about 20°C (4°F). Scientists have been able to determine the amount of CO2 found in the atmosphere during past times, but a direct correlation has not yet been firmly established regarding ambient temperature and the measured past amounts of such gases. The average quantity of atmospheric CO2 which existed during ice ages was 200 ppm, but during interglacial periods it was 280 ppm.
The greenhouse gases have been steadily increasing for the past 200 years, since the beginning of the Industrial Revolution. Carbon dioxide, the most abundant trace gas in our atmosphere, has increased by more than 30% during this time period. It is produced through the burning of wood and fossil fuels, such as coal and petroleum products. It is also released by volcanoes, oceans, decaying plants, and respiration. It is interesting to note that more than 11% of this increase in atmospheric CO2 has come about in only the last 35 years. Today, we measure 360 ppm of CO2 in the present atmosphere, and it is estimated this will reach 600 ppm in about two decades. The last time the Earth's atmosphere held as much as 600 ppm CO2 was during the equable conditions of the Cretaceous Epoch (100 million years ago it actually held as much as 1,000 ppm)...a time when palm trees grew in Siberia and alligators swam in Alaskan waters.
Methane, the second most abundant greenhouse gas, is produced as a by-product of the decomposition of organic material. The most common known sources are swamps, rice paddies, livestock (especially cud-chewing animals), termites, and the use of natural gas. Unstable natural sources of methane hydrates in permafrost regions and oceanic continental slopes are also a potential significant source of atmospheric methane. The level of atmospheric methane is now growing at about 0.1% per year. The level of CFCs in the atmosphere is small by comparison, but these compounds are thousands of times more potent in absorbing heat. They are man-made chemicals and are also implicated in another potentially serious climatic problem- the depletion of the ozone layer. It has been estimated that the present level of greenhouse gases (apart from water vapor) may double in this century, and could raise the Earth’s average temperature by as much as 5° C (9° F).
The interaction of climatic forces is not completely understood, so it is difficult to determine the overall effect of increasing the greenhouse gases. Statistics analyzed from long term records show that the average earthly temperature has indeed increased 0.75° C (1.35° F) during the past 100 years, and that the 10 warmest years recorded duringthat period were all in the last two decades. Temperature increase has been much greater in the Northern Hemisphere (which is mostly land mass) than in the Southern Hemisphere (which is mostly ocean). This is because land readily absorbs radiant energy and therefore heats up quickly (it cools quickly, too), while water has a tremendous capacity to absorb radiant energy and therefore heats up very slowly and moderates the resulting heat radiation. Travel to the Arctic and see that recent years have exhibited a dramatic decrease in sea ice coverage in the Arctic Ocean, with the greatest increase in open water found in the Beaufort and Chukchi seas. So, it should come as no surprise that the greatest temperature increase in the Northern Hemisphere has been within the Arctic environment.
Because of its long history of human occupation since the early 1600s, Svalbard has one of the longest high-latitude meteorological records on Earth. Computer models working on global climate studies have long predicted enhanced greenhouse warming at these high latitudes, which makes the Svalbard record especially interesting. Scientists have directly observed an increase in temperature of about 6°C (11°F) in the past century, and an increase of 4°C (7°F) in just the last three decades.
Most scientists accept that human activities now contribute significantly to the heat budget of the Earth. Although it is not possible yet to determine just how strong this anthropogenic effect really is, many are convinced that most of the warming of the past 50 years is very likely due to human activity. It is important to consider that worldwide climatic variations have been monitored for only a relatively short period of time, and it is difficult to draw solid conclusions and make absolute predictions. Nonetheless, the information we do have indicates to many scientists we may well have started a global warming trend which is irreversible- at least not without drastic changes in our present way of life. One recent study concluded that in order to stop the rise in CO2 levels in our atmosphere, we must halt the net deforestation worldwide immediately and reduce the energy-related emissions of CO2 by 70% of today's production before the year 2030…neither of which are likely to occur. If the average earthly temperature were raised just a few degrees, both the Greenland and Antarctic ice sheets would certainly be affected. If these ice caps were to melt completely, the sea levels worldwide would rise as much as 70 meters (230 feet), thereby flooding most coastal cities and displacing about half the world's human population.
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