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الغيداء · 01-07-2006, 07:22 PM

لو سمحتو ساعدوني بالبحث أبيه هالأسبوع ..

ما عليكم أمر ..

الموضوع عن Global Warning

خال الغيداء ..

سهام الليل · 01-07-2006, 09:22 PM

What is "Global Warming?"

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The term Global Warming refers to the observation that the atmosphere near the Earth's surface is warming, without any implications for the cause or magnitude.?This warming is one of many kinds of climate change that the Earth has gone through in the past and will continue to go through in the future.
Temperature increases will have significant impacts on human activities: where we can live, what food we can grow and how or where we can grow food, and where organisms we consider pests can thrive. To be prepared for the effects of these potential impacts we need to know how much the Earth is warming, for how long the Earth has been warming, and the cause of the warming. Answers to these questions provide us with a better basis for making decisions related to issues such as water resource management and agricultural planning.

What is the Greenhouse Effect?
How is it related to Greenhouse Warming and Global Warming?
The Greenhouse Effect is a term that describes how water vapor, carbon dioxide, and other gases in the atmosphere help maintain the temperature at the Earth's surface.? The atmosphere approximates the function of a greenhouse by first letting sunlight (solar or short wave radiation) pass through to warm the Earth, while absorbing much of the heat (thermal or long wave radiation) radiated up from the surface of the Earth.

Life on Earth would be very different without the Greenhouse Effect. The Greenhouse Effect serves to keep the long term annual average temperature of the Earth approximately 32°C higher than the Earth's temperature would be without the Greenhouse Effect. It is reasonable to expect that the Earth should warm as concentrations of greenhouse gases in the atmosphere increase above natural levels, much like what happens when the windows of a greenhouse are closed on a warm, sunny day. This additional warming is commonly referred to as Greenhouse Warming.

Greenhouse Warming is global warming due to increases in atmospheric greenhouse gases (e.g., carbon dioxide, methane, chlorofluorocarbons, etc.), whereas Global Warming refers only to the observation that the Earth is warming, without any indication of what might be causing the warming.

Global Warming is accepted as fact by most of the scientific community. However, Greenhouse Warming is more controversial because it implies that we know what is causing the Earth to warm. Although it is known for certain that atmospheric concentrations of these greenhouse gases are rising dramatically due to human activity, it is less well known exactly how increases in these greenhouse gases factor in the observed changes of the Earth's climate and global temperatures.

How is the ozone issue different?
The ozone issue and Greenhouse Warming are related yet distinct scientific issues. In the lower atmosphere (called the troposphere), the ozone does act as a greenhouse gas, trapping outgoing radiation that would otherwise escape into space. Compared to carbon dioxide, ozone is a minor greenhouse gas. The significance of tropospheric ozone may be increasing however, due to the burning of fossil fuel which generates ozone (commonly recognized as a component of smog) into the lower atmosphere.

For daily updated images of the ozone, please visit NOAA's Stratosphere: SBUV-2 Total Ozone Page with images of the ozone from the NOAA-14 Satellite by clicking here or on image at right.
Ozone also plays a very important, natural role in the upper atmosphere (called the stratosphere). In the upper atmosphere, ozone acts as a shield against harmful ultraviolet (UV) radiation from the sun. Reductions in stratospheric ozone result in the increase of harmful UV radiation reaching the Earth's surface. Ninety percent of the atmospheric ozone is concentrated 10 to 40 kilometers above the Earth's surface. The biggest destroyer of the ozone in the stratosphere is the set of human produced chemical compounds (chlorofluorocarbons - CFC's), which act as greenhouse gases in the lower atmosphere. Extremely cold stratospheric temperatures over the North and South Poles, combined with solar radiation and atmospheric circulation, amplify the impact of ozone destroying chemical reactions, resulting in "Ozone Holes" over the Antarctica (pictured above) and the Arctic.

http://www.ncdc.noaa.gov/paleo/globalwarming/what.html

سهام الليل · 01-07-2006, 09:26 PM

How do we study "Global Warming?"

There are several ways that scientists study how the Earth's temperature is changing. Although each method has some uncertainties, they all suggest a similar story - that the Earth has warmed dramatically over the last 140 years and that the Earth is now warmer than it has been in the last 600 years.
Some scientists look to satellites to reveal something about the Earth's changing climate. Although the satellite record is very short (ca. 20 years) and hard to interpret due to changes in instruments and orbits, the latest satellite studies confirm the same story - the globe is warming.

The record of instrumental temperature measurements, extending back to the 19th century, provides one clear indication: that the mean annual surface air temperatures of the earth have risen approximately 0.5?C (0.9?F) since 1860.

Paleoclimatic data provides an independent confirmation of this recent warming, and also places the 19th to 20th century (1860 to present day) warming in the context of the last several centuries to millennia. The paleoclimatic record not only allows us to look at global temperature fluctuations over the last several centuries, it also permits scientists to examine past climate even further back in time. This perspective is an important capability in our quest to understand the possible causes of the 20th century global warming. We can look at hypothesized warm periods in the distant past (e.g., 1,000; 6,000; 125,000; and even 165,000,000 years ago) to see if they provide clues for natural processes that could be causing the global warming we are now experiencing. So far, paleoclimatologists have been unable to find any natural climatic explanations for our present-day warming.

http://www.ncdc.noaa.gov/paleo/globalwarming/howdo.html

سهام الليل · 01-07-2006, 09:29 PM

A Final Warning

The goal of a "Paleo Perspective on Global Warming" was to clear up some of the confusion surrounding the issues of global warming, greenhouse warming, the ozone hole, and related change in the Earth's climate system. In particular, we wanted to highlight what paleoclimatic data are, where they come from, and what the data contributes to the global warming debate.
When one reviews all the data, both from thermometers and paleotemperature proxies, it becomes clear that the Earth has warmed significantly over the last 140 years; Global Warming is a reality. Multiple paleoclimatic studies indicate that recent years, the 1990s, and the 20th century are all the warmest, on a global basis, of the last 600, and most likely 1200 years. It appears that the global warming of the last century is unprecedented in the last 1,200 years.

There are, however, questions remaining concerning Global Warming. For instance, what is causing all this warming and what are the implications for the future? The answers to these questions are not simple.

There is considerable debate centered on the cause of 20th century climate change. Few people contest the idea that some of the recent climate changes are likely due to natural processes, such as volcanic eruptions, changes in solar luminosity, and variations generated by natural interactions between parts of the climate system (for example, oceans and the atmosphere). There were significant climate changes before humans were around and there will be non-human causes of climate change in the future.

Just the same, with each year, more and more climate scientists are coming to the conclusion that human activity is also causing the climate of the Earth to change. First on the list of likely human influences is greenhouse warming due to human-caused increases in atmospheric trace-gases. Other human activities are thought to drive climate as well. As this web document points out, there is no doubt that humans are causing the level of atmospheric trace-gases to increase dramatically - the measurements match the predictions. There is also no doubt that these gases will contribute to global warming (since they warmed the Earth before humans). However, there is uncertainty about some issues. For example, these questions remain to be answered with complete confidence:

How much warming has occurred due to anthropogenic increases in atmospheric trace-gas levels?

How much warming will occur in the future?

How fast will this warming take place?

What other kinds of climatic change will be associated with future warming?

Paleoclimatology offers to help answer each of these questions. Several of the paleoclimate studies reported on in this web document (Briffa et al., Mann et al., Overpeck et al.) have begun efforts to attribute past climate change to both natural and human causes, and to use this information to estimate how much of the current warming is due to humans (i.e., greenhouse warming). The best estimate is that about 50% of the observed global warming is now due to greenhouse gas increases. Although this number will continue to be refined, it indicates that the climate modeling community is on target with their estimates that the earth may warm an additional 2 to 7 degrees F in the next century.
What future global warming means to society is beyond the scope of these www pages. However, the paper by Overpeck et al. also includes an analysis of what the unprecedented 20th century warming has meant so far to the Arctic environment. Because the warming already seems to be causing unprecedented changes in glaciers, permafrost, lakes, ecosystems and the oceans, it is likely that future changes will be even more dramatic as the warming continues.

.http://www.ncdc.noaa.gov/paleo/globalwarming/end.html

سهام الليل · 01-07-2006, 09:31 PM

Hope you find the information useful
let me know if you need further help

your sis

**أميرة الغروب** · 01-07-2006, 10:55 PM

thanks dear sister for your help

الغيداء · 01-09-2006, 10:35 PM

مشكورة على المساعدة ..

تسلمين و الله تعبناج ويانا..

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