Global warming is an increase in the
average temperature of the
Earth's atmosphere and
oceans. The term is also used for the scientific
theory of
anthropogenic global warming, which attributes much of the recently observed and projected global warming to a human-induced intensification of the
greenhouse effect. In this theory, the increased volumes of
carbon dioxide and other
greenhouse gases released mainly by the burning of
fossil fuels, and, to a lesser extent, land clearing and agriculture, are the primary sources of warming. The natural greenhouse effect keeps the Earth 30 °
C warmer than it otherwise would be; adding carbon dioxide to an atmosphere, with no other changes, will make a planet's surface warmer. Current research is attempting to further illuminate and quantify the processes and factors that can affect temperature change, especially positive and negative
feedback mechanisms
Temperature change is just one aspect of the broader subject of (human-induced) climate change. The scientific opinion on climate change, as expressed by the UN Intergovernmental Panel on Climate Change (IPCC) and explicitly endorsed by the national science academies of the G8 nations, is that the average global temperature has risen 0.6 ± 0.2 °C since the late 19th century, and that it is likely that "most of the warming observed over the last 50 years is attributable to human activities" [1]. A small minority of qualified scientists contest the view that humanity's actions have played a significant role in increasing recent temperatures. Uncertainties do exist regarding how much climate change should be expected in the future, and a hotly contested political and public debate exists over what actions, if any, should be taken in light of global warming.Global warming is an increase in the average temperature of the Earth's atmosphere and oceans. The term is also used for the scientific theory ofanthropogenic global warming, which attributes much of the recently observed and projected global warming to a human-induced intensification of thegreenhouse effect. In this theory, the increased volumes of carbon dioxide and other greenhouse gases released mainly by the burning of fossil fuels, and, to a lesser extent, land clearing and agriculture, are the primary sources of warming. The natural greenhouse effect keeps the Earth 30 °C warmer than it otherwise would be; adding carbon dioxide to an atmosphere, with no other changes, will make a planet's surface warmer. Current research is attempting to further illuminate and quantify the processes and factors that can affect temperature change, especially positive and negative feedback mechanisms.Based on basic science, observational sensitivity studies, and the climate models referenced by the IPCC, temperatures may increase by 1.4 to 5.8 °C between 1990 and 2100 [2]. This is expected to result in other climate changes including rises in sea level and changes in the amount and pattern ofprecipitation. Such changes may increase the frequency and intensity of extreme weather events such as floods, droughts, heat waves, and hurricanes, change agricultural yields, cause glacier retreat, reduced summer streamflows, or contribute to biological extinctions. Although warming is expected to affect the number and magnitude of these events, it is very difficult to connect any particular event to global warming.
The scientific consensus on global warming is that the Earth is warming, and that humanity's greenhouse gas emissions are making a significant contribution. This consensus is summarized by the findings of the Intergovernmental Panel on Climate Change (IPCC). In the Third Assessment Report, the IPCC concluded that "most of the warming observed over the last 50 years is attributable to human activities". This position was recently supported by an international group of science academies from the G8 countries and Brazil, China and India
Environmental refugees
Even a relatively small rise in sea level would make some densely settled coastal plains uninhabitable and create a significant refugee problem. If the sea level were to rise in excess of 4 metres almost every coastal city in the world would be severely affected, with the potential for major impacts on world-wide trade and economy. Presently, the IPCC predicts sea level rise of less than 1 meter through 2100, but they also warn that global warming during that time may lead to irreversible changes in the Earth's glacial system and ultimately melt enough ice to raise sea level many meters over the next millenia. It is estimated that around 200 million people could be affected by sea level rise, especially in Vietnam, Bangladesh, China, India, Thailand, Philippines,Indonesia and Egypt.
