Environmental Engineering Reference
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such as the one in one hundred year storm, that may suffi ciently disrupt
the system and cause it to move to a new state (Perry et al. 2010).
On the other hand, “climate change” is a significant and lasting
change in the statistical distribution of weather patterns over periods
ranging from decades to millions of years. It may be a change in average
weather conditions, or in the distribution of weather around the average
conditions (e.g., more or fewer extreme weather events) (Smit et al. 2000).
Climate change is caused by factors that include oceanic processes (such
as oceanic circulation), variations in solar radiation received by Earth, plate
tectonics and volcanic eruptions, and human-induced alterations of the
natural world (Brierley and Kingsford 2009). Climate change ( trend ) is
defi ned as the secular change which at present, in the case of temperature,
appears to be increasing and largely anthropogenically-driven, and whose
rate is small as compared to that of the variability at the shorter time scales
(Kelly and Adger 2000). Climate change may also affect climate variability,
for example the frequency of El Niño or extreme events, although large
uncertainties remain (e.g., Collins 2000).
Is Climate change a new story?
Earth's climate has changed (Zachos et al. 2001), and will likely continue to
change (Crowley and Hyde 2008), over multiple time scales. Temperature
change is apparent in the existing instrument record, and numerous proxies
enable past temperature variations to be reconstructed (Mann et al. 2008).
The geological record is punctuated by numerous abrupt changes in
temperature. These discontinuities (for example, the Paleocene-Eocene
Thermal Maximum 56 million years ago, when global temperatures
rose by 6ºC in 20,000 years) defi ne boundaries between epochs of more
consistency lasting tens of millions of years. During the Paleocene-Eocene
Thermal Maximum 1500 to 2000 gigatonnes of carbon was released into
the atmosphere in just 1,000 years; however, that rate is less than the one
at which carbon is being now released through anthropogenic activity
(The Royal Society 2005). Temperatures fell after the Paleocene-Eocene
Thermal Maximum perhaps because of prolifi c growth of marine ferns
Azolla (Brinkhuis et al. 2006), which reduced atmospheric carbon dioxide
concentrations dramatically from 3500 ppm to 650 ppm (Pearson and Palmer
2000), switching Earth from “greenhouse” to “icehouse”. This switch well
illustrates the power of marine biological infl uences on global climate.
Variations in solar activity and Earth's orbit cause cyclical changes
in temperature over tens to hundreds of thousands of years (so called
Milankovitch cycles , according to Lisiecki et al. 2008). Feedback mechanisms
involving greenhouse gases, ocean circulation and ice extent, which in turn
infl uences albedo (the fraction of incoming solar radiation refl ected back to
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