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6.2 CLIMATE CHANGE Earth’s climate is constantly changing. The change can be due to natural causes, such as changes in Earth’s orbit, changes in solar activity, or volcanic eruptions; or anthropogenic, resulting from a change in the composition of Earth’s atmosphere. Since the beginning of the Industrial Era, human activities have led to an increase in the concentration of heat-trapping greenhouse gasses in the atmosphere, which has led to an increase in atmospheric temperature. In fact, the most likely reason for the recent observed warming, since the mid-20th century, is anthropogenic greenhouse gas emissions. 6.2.1 The Greenhouse Effect According to the recent Fifth Assessment Report (AR5) from the International Panel on Climate Change (IPCC; Stocker et al., 2013), the global mean surface temperature has been increasing, and each of the past three decades has been successively warmer (Figure 3). A linear trend, fitted to global average combined land and ocean temperatures, reveals a 0.85 [0.65 to 1.06] °C increase over the period 1880-2012. The temperature on Earth depends on the balance between energy entering and leaving the atmosphere. Incoming energy from the sun can be either reflected back into space or absorbed by Earth’s surface. Some of the energy absorbed is released back into the atmosphere (infrared radiation). Greenhouse gases (water vapor, carbon dioxide, methane, etc.) absorb some of this energy and thus keeps the atmosphere warm. Earth’s average surface temperature, without the greenhouse effect, would be 255 °K (−18 °C), instead of the current 288 °K (15 °C) which enables life as we know it to thrive. Paleoclimatological records from ice cores, corals, lake sediments, tree rings, etc. reveal that the concentr... ... middle of paper ... ...patial extent, duration, and timing of extreme precipitation events, evapotranspiration, tropospheric water content, and runoff may change (National Research Council, 2011), thus influencing the occurrence, nature, and return period of extreme events. Changes at both the lower tail (e.g. reduction in precipitation leading to droughts) and the upper tail (e.g. high intensity rainfall resulting in floods) of range of observed values can be expected. These changes may be in the following three ways: (i) a shift in the mean which will result in less low magnitude events and more high magnitude events; (ii) an increase in standard deviation and thus variability which equates with more low and high magnitude events; and (iii) a change in the shape of the distribution where low magnitude events remains almost constant but an increase in high magnitude events (IPCC, 2012).

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