Changes in Carbon Dioxide levels over time. Image courtesy of NASA. Click image for full size.
Changes in the Earth's climate over the past thousands of years can be reconstructed using a combination of direct measurements from land and ocean weather stations and indirect proxy methods, which include tree rings and pollen and plankton from lakes and ocean sediment cores. These records indicate that the Earth's climate has cycled through many warming and cooling periods over geologic times. Ancient samples of atmospheric gases from ice cores reveal that the concentration of greenhouse gases (GHGs) in the atmosphere has also fluctuated in the past, with high GHG levels being correlated with warmer global temperatures. Cycles in temperature and GHG concentrations over geologic time scales have been caused by natural fluctuations in incoming solar radiation and the chemical composition of the atmosphere.
Anthropogenic Climate Changes
The 2007 Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) details the unequivocal warming of the Earth's climate over the last 50 years, most of which is very likely a result of increases in anthropogenic GHG emissions. There has been a rapid 35% rise in atmospheric GHG concentrations since preindustrial times, and in 2005, atmospheric GHG concentrations were higher than any levels recorded or estimated for the previous 650,000 years.
In addition to changes in temperature and precipitation means, greenhouse warming will also lead to increased climate variability and the occurrence of climatic extremes. For example, many areas across the globe are predicted to experience more severe droughts, floods, large-scale erosion and soil wasting, landslides, and extreme heat events. Changes in these extreme events will have significant impacts on disturbance processes that are important to many ecosystems. Wildfires are influenced by the availability of fuel loads and occurrence of ignition triggers, but climate conditions are also critical in determining the severity and extent of wildfires. Extremely hot and dry conditions can lead to more ignition-prone fuel as well as to fires that burn hotter and therefore can have more extreme effects on vegetation. Fire trends from 1970 to the present in the western United States have increased in frequency and duration, and fire seasons have become longer since the mid-1980s (Westerling et al., 2006).
~ Read the entire article in CREDO Conservation and Global Climate Change from The Princeton Guide to Ecology (login with your COM account for off campus access)..
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