BEIJING, Dec. 1 (Xinhua) -- Reports show that emissions resulting from human activities, in particular, the burning of fossil fuels, are increasing the world's atmospheric concentrations of greenhouses gases to unprecedented levels.
Greenhouse gases, such as carbon dioxide, methane, sulfur hexafluoride and per fluorocarbons, are gases that can keep part of the heat received from solar or geothermic sources within the earth's atmosphere.
Carbon dioxide, or CO2, is the most powerful greenhouse gas, which, according to scientific research, can stay in the atmosphere for 50 to 200 years, once it is produced.
According to statistics from the World Meteorological Organization (WMO), the decade of 1998-2007 is the warmest on record, and the earth average temperature has risen by 0.74 degree centigrade in the past century.
The Fourth Assessment Report released by the United Nations Intergovernmental Panel on Climate Change (IPCC) in 2007, which incorporates work of around 2500 scientists from more than 130 countries, warned the world that the possibility of human-induced global warming was higher than 90 percent.
The IPCC says such a hypothesis has become more and more credible, based on their evaluations on climate change that are drawn from scientific and technological research and social economic data from the past 20 years.
In its first assessment in 1990, the IPCC started to take into consideration human activities as a reason for climate change, but also pointed out the possibility of natural fluctuation.
A report six years later said scientists had discovered more evidence indicating that human kind's impact on the climate was emerging.
Then, a third report published in 2001 provided even newer and stronger evidence to lay the blame on human beings, with a conclusion that, over the past half a century, there was a 66 percent possibility that global warming was the consequence of human activities.
As the 2007 IPCC report suggests, since the start of the industrial revolution in the western world in the mid-eighteenth century, the concentrations of greenhouse gases in the earth's atmosphere have kept rising and the CO2 concentration is now at the highest level in 650,000 years.
The average temperature on the earth in the last decade of the 21st century would be 4 degrees higher than that in the same period in the 20th century, if the world failed to weaken its dependence on carbon-based fuels, said the latest report.
Some experts say developed economies emitted greenhouse gases such as carbon dioxide in an unconstrained manner on their way to industrialization and modernization.
They accounted for 95 percent of the CO2 emissions from the post-industrial revolution era to 1950. In the next half a century, the figure was still as high as 77 percent.
Today, developed countries, which hold only about one fifth of the world's population, are consuming more than 70 percent of the world's energy and discharging over half of the greenhouse gas on the globe.
Per capita emissions in most developed countries are far higher than the world's average.
So those countries are expected to take the lead in substantially cutting emissions, based on the principles of the UN Framework Convention on Climate Change and the Kyoto Protocol.
They should also continue to devote themselves to the cause and provide capital and technological assistance to developing countries to help them cope with climate change even after the end of the first commitment period of the Protocol in 2012.
