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Autor: anton • November 15, 2010 • 1,764 Words (8 Pages) • 849 Views
Global Climate Change
Is the world getting warmer or cooler, and is it because of the actions of humans to blame or is it just a natural cycle?
Scientists are concerned that increases in the amount of the greenhouse gas carbon dioxide will result in worldwide temperature increases that will affect the ecosystems of the planet. In the short-term, several species would be expected to become extinct. It is possible that a runaway greenhouse effect could make the earth uninhabitable by all species including us!
CO2 Levels for the Last 650,000 Years
As shown, CO2 levels go through cycles of increase and decrease over 100,000 year intervals, which correspond to eccentricity changes in the earth's orbit. The atmospheric concentration of CO2 was relatively constant at about 280 parts per million (ppm) for about1,000 years before 1750. Since 1750, the CO2 concentration has risen, reaching about 377 ppm in 2005. The inset (small graph in upper right) of figure 1 shows the atmospheric levels of CO2 for the last 44 years. During that short period of time, CO2 levels have risen nearly 60 ppm, producing the sharp spike at the far right of the main graph. Although the cycles of CO2 levels (approximately 100,000 years apart) are naturally on a rise from the last ice age, the spike is dramatically higher than any levels seen over the last 650,000 years. This data strongly suggest that the rapid increase of CO2 in the last century is not the result of a natural process. At the current rate of increase, atmospheric CO2 levels will double in approximately 150 years.
Annual Carbon Emissions vs. Atmospheric CO2 Levels
We are producing much more CO2 than is showing up in the atmosphere. The blue line on the left shows the amount of carbon emissions over time, compared to the red line, which is the average amount of carbon showing up in the atmosphere. As the Graph shows, only about half of carbon emissions can be found in the atmosphere. What happens to the rest? Originally, researchers had thought that all the extra carbon dissolved in the oceans. However further study revealed that the oceans were not as efficient carbon sinks as previously thought. Additional carbon sinks have been found that make up most of the difference. One is the "fertilization effect," that higher CO2 levels have upon photosynthesis. Which means, plants grow faster and fix more atmospheric carbon the higher the concentration of CO2. In addition, it seems that northern latitude forests fix more atmospheric carbon than previously thought.
So, we know that CO2 levels are rapidly increasing and will probably continue to do so for the foreseeable future. A probable doubling of CO2 levels within the next 150 years will result in global temperature increases. The magnitude of these increases is difficult to estimate at this time, although climate models put the increase between 1.4o and 5.8oC.
Equally important is whether there is a difference between energy influxes from the Sun vs. radiation of thermal energy from the earth into space.
Temperatures will increase only if the net influx of energy exceeds the radiation of the Worldwide Temperature Changes Since 1880. energy back to space. A study from 2005 revealed that the Earth is absorbing 0.85 watts per square meter more energy from the Sun than it is emitting to space, confirming that the earth is warming, and will continue to do so, even without a change in either solar influx or radiation of heat from the earth.
Much of the excess energy is being "stored" in the earth's oceans, which moderate the amount of temperature change observed on the earth's surface. Even so, surface temperatures have risen about 0.6oC since the late 1970's However, the trend line (in red) shows that changes in temperature have not been directly proportional to changes in CO2 levels in the atmosphere (which have been steadily increasing). The graph shows periods of increasing temperatures interspersed with periods of no or even negative temperature changes.. It would seem that at least part of the current increase may be part of a natural cycle. However, the slope of the current increase is much steeper than that of the previous period of temperature increase (1920-1940), suggesting that at least part of the increase is not the result of a natural cycle.
This diagram depicts the basic components that influence the state of the Earth's climatic system. Changes in the state of this system can occur externally (from extraterrestrial systems) or internally (from ocean, atmosphere and land systems) through any one of the described components. For example, an external change may involve a variation in the sun's output which would externally vary the amount of solar radiation received by the Earth's atmosphere and surface. Internal variations in the Earth's climatic system may be caused by changes in the concentrations of atmospheric gases, mountain building, volcanic activity, and changes in surface or atmospheric reflection of the sun's light.
The work of climatologists has found evidence to suggest that only a limited number of factors are primarily responsible for most of the past episodes of climate change on the Earth. These factors include:
* Variations in the Earth's orbital characteristics.
* Atmospheric carbon dioxide variations.
* Volcanic eruptions
* Variations in solar output.
Temperatures over the history of the earth
Numerous studies have shown that temperatures in the past have been warmer than what we now experience. Studies suggest that the medieval warm period (from the ninth to thirteenth centuries) was up to 1oC warmer than today. This warm period was followed by the "Little Ice Age", which went from 1400 to 1840, during which time temperatures were significantly cooler than present. This period of cooling was only the last in a series of climate cycles that happen every 1,500 years. Scientists believe that these variations in temperature are due to changes in solar output, the orbit of the earth, and/or changes in ocean currents. For Eastern North America and Western Europe, temperatures are moderated by warm currents moving northward from the tropics. This "thermohaline" circulation occurs as the result of the temperature and saltiness of the ocean water. Cold water is "heavier" than warm water and salty water