Global warming is a result of the build-up of greenhouse gases in the atmosphere. These, in turn, are being released into the air by man-made activities such as fossil-fuel burning in power plants, vehicles, cutting trees, etc. Besides, we have created new, more powerful GHGs (such as chlorofluorocarbons, CFCs) and released them into the atmosphere. Greenhouse gases are very efficient trappers of the sun’s heat and over the last century, have contributed to a rise in the average surface temperature of the earth.
More on global warming

Knowledge about global warming related to man's activities comes mostly from indirect sources of information. One form of evidence comes from studies on the annual rings of tree trunks. These are pointers to the growth of a tree: rapid growth suggests higher temperatures and increased moisture in the environment. For example, researchers studying trees in Mongolia have found unusually high growth rates during the last century indicating that temperatures were higher in this period.
 

No, these changes are not anything new. Climate change is a natural phenomenon and has been occurring ever since the earth was formed. There have been well-marked warm and cold periods for the last 400 000 years. The last Ice Age occurred about 10,000 years ago and large parts of Europe and North America were covered with ice. Between the 10th and 14th centuries, the global temperature rose by about 1ºC. So, climate change is by no means, anything new but there is an important difference between what happened then and what’s happening now. Historically, climate change took place naturally, but the latest phenomenon is a result of man’s interference with natural processes, at a rate too rapid to allow ecosystems and their habitat to adapt. If you want to know more about changes that took place in the past, visit the global warming section of The Why Flies web site, developed by the  University of Wisconsin-Madison.
  

Yes, it has. Climatic patterns for the last 35-50 years show that man-made activities have definitely had an impact. Models created by scientists to explain the variations in temperature over the last 140 years cannot be explained by natural factors alone. The best agreement (between actual observations and estimations) is obtained when a combination of both, man-made (such as GHG’s) and natural factors (volcanic eruptions, for example) is taken into account. Closer home, in Nepal, scientists have been observing increasing temperatures in the Himalayas since the 1970s which could lead to floods and lakes bursting their banks.
     

A warmer climate will change rainfall and snowfall patterns, lead to increased droughts and floods, cause melting of glaciers and polar ice sheets, and result in a sea-level rise. This, in turn, will affect water resources, forests and other natural ecological systems, agriculture, power generation, infrastructure, tourism, and human health. Most importantly, a rise in ocean temperature as a consequence of climate change could affect the intensity and frequency of a weather phenomenon called the El Nino in the Pacific Ocean.
     

El Nino is a shift in ocean temperatures and atmospheric conditions in the tropical Pacific that disrupts weather around the world. It is a poorly understood cyclical phenomenon that can lead to terrible extremes of weather all over the world. The warm El Nino phase typically lasts for 8–10 months or so.
More on El Nino
   

Plenty. There are several things at the society, community and individual level that we can do. The very first initiative is to share with as many people as we can, what we know about climate change. We can help to create a level of opinion that will convince our policy-makers and industry that action is necessary.

As an individual, you can contribute by doing simple things such as switching off fans and lights when not in use, and using public transport whenever possible.

Yes, most nations are getting together under the aegis of the United Nations to think of solutions and ways to achieve them. Some prominent efforts are the Montreal Protocol (1987) which sought to phase out CFCs (chlorofluorocarbons) and the UNFCCC (United Nations Framework Convention on Climate Change), which aims to reduce GHGs. Countries agreed on the UNFCCC at the Rio Earth Summit in 1992. This Summit brought global attention to the fact that environmental problems were linked to economic conditions and poverty. It laid stress on sustainable development and conservation. In 1997, the UNFCCC reached a historic agreement to reduce GHG emissions in Kyoto. The most significant part of the Kyoto Protocol was the binding commitments by countries to reduce emissions.

Despite the fact that India's contributions to greenhouse gas emissions are very small, the Government is still taking measures to introduce climate-friendly initiatives.The Ministry of Environment and Forests is the nodal agency for climate change issues in India. India has initiated several climate-friendly measures, particularly in the area of renewable energy. It has one of the most active renewable energy programmes besides having perhaps, the only dedicated ministry for non-conventional energy sources in the world. In the rural areas, solar photovoltaic power systems have been put to use for lighting homes and pumping water, while other applications include railway signalling and TV transmission.Our country is among the top five in the world in the generation of wind power, with an installed capacity of 1507 MW. Another major climate-friendly initiative has been launched in the area of forestry. A National Forests Policy has been drawn up, in which the programme of Joint Forest Management looks at meeting the requirements of fuel wood, fodder and timber with the local people’s participation.The Indian government signed the UNFCCC in June 1992. Under theConvention it has to make an inventory of the country’s GHG emissions, and, identify areas vulnerable to the effects of climate change.The UNFCCC promotes and reviews the implementation of the Convention through decisions taken at annually-held meetings of the Conference of Parties (COP). This year’s conference (COP 8) is being hosted by India and will be held in New Delhi between 23 October and 1 November, 2002.