The earth's climate is dynamic and changing through a natural cycle. The causes of climate change can be divided into two categories -- those that are due to natural causes and those that are created by man.

There are a number of natural factors responsible for climate change, such as variations in solar radiation, deviations in the Earth's orbit, volcanoes, continental drift and ocean drift.

On the other hand, human activities, especially those since the Industrial Revolution in the 19th century, have contributed mainly to the climate change which is currently characterized by global warming.

The first world climate conference was held on February 12-23, 1979, in Geneva, at which scientists sent warnings on global warming while climate change was for the first time put on the agenda.

The conference also led to the creation of the Intergovernmental Panel on Climate Change (IPCC) by the World Meteorological Organization (WMO) and the United Nations Environment Program (UNEP) in 1988.

So far, the IPCC has published four assessment reports. In its last assessment report in 2007, the IPCC said with 90 percent certainty that human activities, especially the burning of fossil fuels, had caused global warming during the past 50 years.

The fourth report is the largest and most detailed summary of the climate change situation ever undertaken, involving some 2,500 scientists from more than 130 countries.

It notes that "carbon dioxide, methane, and nitrous oxide have increased markedly as a result of human activities since 1750 and far exceeded pre-industrial values."

It also states that "evidence from all continents and most oceans shows that many natural systems are being affected by regional climate changes, particularly temperature increases."

(Xinhua News Agency December 7, 2009)