Is the Earth’s climate changing?  The answer is unequivocally “Yes”.
The more difficult question is “Why is it changing?”.
IPCC Third Assessment Report, 2001

At present the mankind is standing on a threshold of global climate change caused by the anthropogenic activity. The Third Assessment Report, 2001 of the Intergovernmental Panel on Climate Change (IPCC) states:

“Intensive climate research and monitoring
gives scientists much greater confidence in their understanding
of the causes and consequences of global warming”.

The Assessment presents a compelling snapshot of what the earth will probably look like in the late 21st century, when a global warming of 1.4-5.8°C (2.5-10.4°F) will influence weather patterns, water resources, the cycling of the seasons, ecosystems, extreme climate events, and much more.

Here are the most indicative facts:

• The global average surface temperature has increased over the 20th century by about 0.6°C.
• The 1990s was the warmest decade and 1998 the warmest year in the instrumental record, since 1861.
• The increase in temperature in the 20th century has been the largest of any century during the past 1000 years.
• The extent of snow cover has decreased of about 10% since the late 1960s.
• Northern Hemisphere spring and summer sea-ice extent has decreased by about 10 to 15% since the 1950s.
• The global average sea level has risen between 0.1 and 0.2 meters during the 20th century.

Even greater changes are expected in the more distant future. The international community is working together to minimize these risks through the 1992 Framework Convention on Climate Change and its 1997 Kyoto Protocol. Under their frames, governments need to move forward quickly to design and carry out their national climate change policies. The well-designed, market-oriented policies can reduce emissions and the costs of adapting to the unavoidable impacts of climate change while simultaneously generating significant economic benefits. These benefits include more cost-effective energy systems, more rapid technological innovation, reduced expenditures on inappropriate subsidies, and more efficient markets. Cutting emissions can also reduce damage from local environmental problems, including the health effects of air pollution.