davecpa

that is great you recycle your cans... but i dont think that is going to stop global warming...The greenhouse effect is unquestionably real and helps to regulate the temperature of our planet. It is essential for life on Earth and is one of Earth's natural processes. It is the result of heat absorption by certain gases in the atmosphere (called greenhouse gases because they effectively 'trap' heat in the lower atmosphere) and re-radiation downward of some of that heat. Water vapor is the most abundant greenhouse gas, followed by carbon dioxide and other trace gases. Without a natural greenhouse effect, the temperature of the Earth would be about zero degrees F (-18°C) instead of its present 57°F (14°C). So, the concern is not with the fact that we have a greenhouse effect, but whether human activities are leading to an enhancement of the greenhouse effect.


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Are greenhouse gases increasing?
Human activity has been increasing the concentration of greenhouse gases in the atmosphere (mostly carbon dioxide from combustion of coal, oil, and gas; plus a few other trace gases). There is no scientific debate on this point. Pre-industrial levels of carbon dioxide (prior to the start of the Industrial Revolution) were about 280 parts per million by volume (ppmv), and current levels are about 370 ppmv. The concentration of CO2 in our atmosphere today, has not been exceeded in the last 420,000 years, and likely not in the last 20 million years. According to the IPCC Special Report on Emission Scenarios (SRES), by the end of the 21st century, we could expect to see carbon dioxide concentrations of anywhere from 490 to 1260 ppm (75-350% above the pre-industrial concentration).


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Is the climate warming?
Yes. Global surface temperatures have increased about 0.6°C (plus or minus 0.2°C) since the late-19th century, and about 0.4°F (0.2 to 0.3°C) over the past 25 years (the period with the most credible data). The warming has not been globally uniform. Some areas (including parts of the southeastern U.S.) have, in fact, cooled over the last century. The recent warmth has been greatest over North America and Eurasia between 40 and 70°N. Warming, assisted by the record El Niño of 1997-1998, has continued right up to the present, with 2001 being the second warmest year on record after 1998.Indirect indicators of warming such as borehole temperatures, snow cover, and glacier recession data, are in substantial agreement with the more direct indicators of recent warmth. Evidence such as changes in glacier length is useful since it not only provides qualitative support for existing meteorological data, but glaciers often exist in places too remote to support meteorological stations, the records of glacial advance and retreat often extend back further than weather station records, and glaciers are usually at much higher alititudes that weather stations allowing us more insight into temperature changes higher in the atmosphere.

Large-scale measurements of sea-ice have only been possible since the satellite era, but through looking at a number of different satellite estimates, it has been determined that Arctic sea ice has decreased between 1973 and 1996 at a rate of -2.8 +/- 0.3%/decade. Although this seems to correspond to a general increase in temperature over the same period, there are lots of quasi-cyclic atmospheric dynamics (for example the Arctic Oscillation) which may also influence the extent and thickness of sea-ice in the Arctic. Sea-ice in the Antarctic has shown very little trend over the same period, or even a slight increase since 1979. Though extending the Antarctic sea-ice record back in time is more difficult due to the lack of direct observations in this part of the world.


For the Northern Hemisphere summer temperature, recent decades