- Global warming is the increase in the average measured temperature of the Earth's near-surface air and oceansnd since the mid-twentieth century, and its projected continuation.
WHY??? ~ Causes:
- External forcing, including variations in the earth's orbit around the Sun (orbital forcing), changes in solar luminosity, volcanic eruptions, and atmospheric greenhouse gas concentrations.
(The greenhouse effect is the process by which absorption and emission of infared radiation by atmospheric gases warm a planet's lower atmosphere and surface.)
- Human activity since the industrial revolution has increased the concentration of various greenhouse gases, leading to increased radiative forcing from CO2, methane, tropospheric ozone, CFCs and nitrous oxide.
HOW??? ~ Effects:
- cause more water to evaporate into the atmosphere.
- clouds emit infrared radiation back to the surface, and so exert a warming effect
- will reduce the decrease of temperature with height, producing a negative lapse rate feedback that weakens the greenhouse effect.
- ice near the poles melts at an increasing rate, then land or open water takes its place. Both land and open water are on average less reflective than ice, and thus absorb more solar radiation.
- release of CO2 and CH4 from thawing permafrost, such as the frozen peat bogs in Siberia, is an additional mechanism that could contribute to warming.
- the resulting low nutrient levels of the mesopelagic limits the growth of diatoms in favor of smaller phytoplankton that are poorer biological pumps of carbon. So, the ocean's ability to sequester carbon decline as it warms.
HOW & HOW??? ~Attributed and expected effects:
- glacial retreat
- Arctic shrinkage
- worldwide sea level rise
- flooding and drought.
- changes in the frequency and intensity of extreme weather events
- changes in agricultural yields
- reduced summer streamflows
- increases in the range of disease vectors
- increasing deaths
- economic losses projected
- species extinctions
http://en.wikipedia.org/wiki/Global_warming#cite_note-77
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