A new report by a UN panel of climate scientists says it is "extremely likely" that global warming is man-made.
In a summary of the report published on September 27 in Stockholm, the Intergovernmental Panel on Climate Change (IPCC) used the strongest words yet in its assessment of the state of the world's climate.
Michel Jarraud, the secretary-general of the World Meteorological Organization, told a news conference in Stockholm that the findings should be regarded as a "wake-up call."
"Now this report confirms -- and you will hear a lot more about it, with even more certainty than in the past -- that it is extremely likely that changes in the climate system for the past half-a-century are due to human influence," Jarraud said.
"And it should serve as yet another wake-up call that our activities today will have a profound impact on society, not only for us but for many generations to come."
The document raised the probability that most global warming is manmade to 95 percent -- up from 90 percent in its previous report in 2007.
The IPCC also raised its projections of the rise in sea levels to 26-82 centimeters by the end of the century. The previous report, in 2007, predicted a rise of 18-59 centimeters.
It said that climate warming was "unequivocal" on the ground, in the air, and in the oceans, and argued that a pause in warming over the past 15 years was too short to reflect long-term trends.
"Observations of changes in the climate system are based on multiple lines of independent evidence," said Qin Dahe, co-chairman of IPCC Working Group I.
"Our assessment of the science finds that the atmosphere and ocean have warmed, the amount of snow and ice has diminished, the global mean sea level has risen and the concentrations of greenhouse gases have increased."
The full 2,000-page report will be released on September 30.
'Yet Another Wake-Up Call'
The new document is the first volume in an IPCC trilogy to be published over the next 12 months that seeks to determine the status of global warming and its impact.
The report is likely to spark renewed controversy, as previous IPCC assessments have been targeted in the past by climate skeptics as biased or flawed.
IPCC chief Rajendra Pachauri was himself the center of a scandal in 2010 over the inclusion in a previous IPCC report of incorrect claims that the Himalayan glaciers could melt away by 2035.
UN Secretary-General Ban Ki-moon has called for a summit on climate change at the world body in September 2014.
In a first reaction, U.S. Secretary of State John Kerry issued a statement saying the report was "yet another wake-up call" and urging strong action to battle the impacts of climate change.
Political interest in dealing with climate change diminished drastically after a failed UN summit in Copenhagen in 2009 and amid economic recession in many developed countries.
With reporting by AP and BBC