Researchers around the globe have found that climate change is likely to impact water resources depletion and pollution significantly. There have been observed changes in surface temperature, rainfall, evaporation, and extreme events since the beginning of the 20th century. The atmospheric concentration of CO2 has increased from about 280 parts per million by volume (ppmv) to about 369 ppmv, and the global temperature of the Earth has increased by about 0.6 degrees C. The present CO2 concentration has not been exceeded during the past 420,000 years and likely not during the past 20 million years. The current rate of atmospheric CO2 level increase is unprecedented during at least the past 20,000 years. About 75 percent of the anthropogenic emissions of CO2 to the atmosphere during the past 20 years is attributed to fossil fuel burning. The rest is predominantly due to land-use change, especially deforestation.
The globally averaged surface temperature is projected to increase by 1.4 to 5.8 degrees C 1990-2100. The global mean sea level has risen by 4-8 in. (10-20 cm.). The average global surface temperature is projected to increase by 1.4-3.0 degrees C 1990-2100 for low-emission scenarios, and 2.5-5.8 degrees C for higher emission scenarios of greenhouse gases in the atmosphere. Over the same period, associated rise in global mean sea level is projected between 1.3-13.6 sq. in. (9-88 sq. cm.).
A number of researchers have reported the impact of climate-change scenarios on hydrology of various basins and regions; they project that increasing temperature and decline in rainfall may reduce net recharge and affect freshwater resources. Human-caused influences are expected to follow a steady growth trend in the future; climate modifications caused by anthropogenic radiative forcing are considered to be more permanent than those caused by natural variability factors.
According to the Intergovernmental Panel on Climate Change (IPCC), since the Industrial Revolution began in the mid-16th century, CO2 levels in the atmosphere have increased by 35 percent and the atmospheric concentration of CH4 has increased by 1060 parts per billion (151 percent) and will continue to increase. The present CH4 concentration has not been exceeded during the past 420,000 years. The inter-annual growth in CH4 level slowed and became significantly variable in the 1990s, compared with the 1980s. It has been suggested that a significant ratio of the current CH4 emissions are anthropogenic rather than natural. The anthropogenic sources of methane include the consumption of fossil fuels, cattle, paddy rice fields, and landfills. Recent studies have indicted carbon monoxide (CO) emissions as a cause of increasing atmospheric CH4 concentration.
In addition, the emissions of persistent GHGs such as CO, NO, PFCs, and SF, could continue to have
long-term impacts on atmospheric composition, radiative forcing, and climate elements. This could imply that anthropogenic climate change may persist for a long time to come. The enhanced atmospheric concentrations of GHGs are implicated as the primary cause of global warming.
Recent findings by the IPCC indicate that the atmospheric concentration of CO2 in 2005 was 375 ppm compared to the pre-industrial levels of 280 ppm. This has contributed to the increase in the Earth's surface temperature by 0.6 degrees C (one degree F). Worldwide measurements of sea level have demonstrated a rise of about 0.56 ft. (0.17 m.) during the 20th century. The world's glaciers have, over time, receded steadily and Arctic sea ice extent has steadily shrunk by 2.7 percent per decade since 1978.
Glaciers are an intriguing part of the Earth's natural environment and have been identified as one of the significant and sensitive indicators of climate change. Their size, lifespan, and timescale information of accumulation and ablation, or growth and collapse (glacier retreat) are primarily attributed to change in climate elements such as temperature, precipitation, wind speed, humidity, and solar radiation.
Increased surface temperatures of the Earth are causing glaciers to melt faster than winter snows can replenish them. Melting sea ice may eventually lead to global changes in water resources and circulation, and melting ice could speed up warming of the Arctic because water absorbs much more heat than ice. Extreme and ongoing declines in the thickness and extent of Arctic sea ice will pose enormous consequences for the Arctic population, their ecosystems, and coastal evolution. As the glaciers shrink, a greater portion of the Earth's water will enter the liquid phase and becomes available to the oceans and the atmosphere. This will ultimately result in a increased volume of water in the oceans, which could lead to a significant rise in sea level.
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