Paris, Feb 2 (DPA) Human activity is unequivocally driving climate change and unless it is modified, it will cause temperatures to rise by as much as 6.4 degrees Celsius by the end of the century, the Intergovernmental Panel on Climate Change (IPCC) said in a report issued Friday in Paris.

'Warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global mean sea levels,' the United Nations-overseen IPCC said in a summary of the report.

Eleven of the past 12 years (1995-2006) rank among the warmest years on record of global temperatures, the report noted, 'Most of the observed increase in globally averaged temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations.'

It said, 'Global atmospheric concentrations of carbon dioxide, methane and nitrous oxide have increased markedly as a result of human activities since 1750 and now far exceed pre-industrial values.'

The increase in carbon dioxide in the atmosphere is primarily due to the use of fossil fuels, the report said, while those of methane and nitrous oxide were primarily due to agriculture.

'Continued greenhouse gas emissions at or above current rates would cause further warming and induce many changes in the global climate system during the 21st century that would very likely be larger than those observed during the 20th century.'

According to several estimates, these changes will raise global temperatures by an average of 1.1 to 6.4 degrees, depending on the scenario used by the scientists.

As a result of rising temperatures, glaciers and snow cover have decreased in both hemispheres, with glacier and ice-cap melt leading to a rise in sea levels, the report said.

In addition, 'Numerous long-term changes in climate have been observed,' the IPCC noted.

These include changes in Arctic temperatures and ice, precipitation amounts, ocean salinity, wind patterns and aspects of extreme weather, including droughts and the intensity of tropical cyclones.

Arctic temperatures increased at almost twice the global average rate in the past 100 years, the report said, while satellite data since 1978 reveals that the extent of the Arctic sea ice has shrunk by 2.7 percent per decade on the average.