U.N. global warming report puts humans on the hot seat

• IPCC climate report is the U.N.-sponsored body%27s fifth
• Report says global warming is %27unequivocal%27
• Global surface temperatures are %22likely%22 to be at least 2.7 degrees above pre-industrial levels by 2100

Global warming is "unequivocal" and it is "extremely likely" that humans are the primary contributors to this warming, according to a report released Friday morning in Stockholm by the U.N.-created Intergovernmental Panel on Climate Change (IPCC), the world's top climate research group.

"Human influence has been detected in warming of the atmosphere and the ocean, in changes in the global water cycle, in reductions in snow and ice, in global mean sea level rise, and in changes in some climate extremes," the report says.

The report says that it is now more certain than ever that "human influence has been the dominant cause of the observed warming" since the 1950s.

The report says that "each of the last three decades has been successively warmer at the Earth's surface than any preceding decade since 1850" and that in "the Northern Hemisphere, 1983–2012, was likely the warmest 30-year period of the last 1400 years."

As for the supposed "pause" in global warming since 1998, the report says that this may be due to changing climate models and that a fuller understanding of this pattern requires further study.

"Due to natural variability, trends based on short records are very sensitive to the beginning and end dates and do not in general reflect long-term climate trends," the report says.

The report says that it is "extremely likely" that more than half of the observed global warming from 1950 is caused by an increase in greenhouse gases emissions.

Other findings:

• The atmospheric concentrations of carbon dioxide, methane, and nitrous oxide have increased to levels unprecedented in at least the last 800,000 years. Carbon dioxide concentrations have increased by 40% since pre-industrial times, primarily from fossil fuel emissions.

• There is "high confidence" that the rate of sea-level rise since the mid-19th century has been larger than the mean rate during the previous two millenniums. Over the period 1901-2010, global mean sea level rose by about 7.4 inches. Global mean sea level will continue to rise during the 21st century, with a projected range of from 10-32 inches.

• There is "high confidence" that over the last two decades, the Greenland and Antarctic ice sheets have been losing mass, glaciers have continued to shrink almost worldwide, and Arctic sea ice and Northern Hemisphere spring snow cover have continued to decrease in extent.

• Global surface temperatures are "likely" to be at least 2.7 degrees above pre-industrial levels by the year 2100, and will likely range from 4.7 to 8.6 degrees above the levels seen in 1986-2005.

What was released Friday morning is a short "summary for policymakers" of the full 2,000-page report, which will be released Monday.

The report is "the world's most rigorous and important scientific report in history," says meteorologist Jeff Masters of the Weather Underground, a private meteorology firm.

The IPCC "has put together an amazingly authoritative and comprehensive report on a subject crucial to the future of civilization, a report that will guide policymakers worldwide as they struggle to cope with the growing chaos generated by the great climate disruption that is already upon us," he says.

"There's now no denying that climate change is real and it's impacts are occurring faster and are worse than we could have predicted even six years ago," stated Durwood Zaelke, president of the Institute for Governance and Sustainable Development, a non-profit group in Washington, D.C.

"This landmark report underscores the importance of the Obama administration's efforts to curb carbon pollution, and I will do everything in my power to support the administration in their efforts to address the dangerous impacts of climate disruption," Sen. Barbara Boxer, D-Calif., said in a statement. Boxer is chairman of the Senate's Environment and Public Works Committee.

The report is based on research by hundreds of the world's top climate scientists. This one covers the physical science of climate change, and will be followed over the next 14 months by three more reports on climate change impacts, mitigation, along with a synthesis of the previous reports.

The IPCC releases reports every few years that synthesize the latest in peer-reviewed research. This is its fifth assessment and the first since 2007.

Following the report's release, U.N. Secretary General Ban Ki Moon said Friday: "The heat is on. Now we must act."