Human influence on the planet's climate is clear and having "widespread and consequential impacts on human and natural systems," some of which may be irreversible, says a draft report out today from a United Nations science panel.
"Warming of the climate system is unequivocal, and since the 1950s, many of the observed changes are unprecedented over decades to millennia," the report says. "The atmosphere and ocean have warmed, the amounts of snow and ice have diminished, and sea level has risen."
Changes in many extreme weather and climate events have been seen in the past six decades or so, including fewer cold temperature extremes and more hot temperature extremes.
The U.N. Intergovernmental Panel on Climate Change (IPCC) document is the final part of the group's Fifth Assessment Report, which synthesizes three earlier large reports on various aspects of climate change. There's little in this document not covered in the others, but the language is more stark.
"The idea of the synthesis report is that, as the title implies, it is a synthesis of the assessment results from the three previous IPCC Working Groups," said Gerald Meehl, a senior scientist at the National Center for Atmospheric Research. The three previous reports covered physical climate science; impacts and adaptation; and mitigation.
"The synthesis report a unique contribution in understanding the integrated physical and human aspects of the climate change problem," Meehl said.
The IPCC is a group of researchers and scientists from around the world who monitor recent climate science and release reports every several years about the latest scientific findings.
The report states that the cause of this climate change is man-made emissions of greenhouse gases, which are "the highest in history" and probably "unprecedented in at least the last 800,000 years."
The recent uptick in carbon dioxide levels is correlated with a rise in global temperatures of about 1.5 degrees since the early 1800s.
"Without additional mitigation, and even with adaptation, warming by the end of the 21st century will lead to high to very high risk of severe, widespread and irreversible impacts globally, " it says.
"Each year, reports like the IPCC use stronger language and rest on a growing number of studies showing that greenhouse gas emissions are warming the planet," said climate change expert Jessica Hellmann, the associate professor of biological sciences at the University of Notre Dame.
"The report explains that we are approaching a global tipping point," she added. "If we cross this point, we will see huge changes in ecosystems, our ability to grow food, and increased human suffering from flood, heat, drought, and sea level rise."
The report says that if carbon dioxide and other greenhouse gases continue to be emitted at the current rate, it's likely that by 2050, temperatures will rise by about 3.6 degrees Fahrenheit, when compared with the temperatures from 1986 to 2005.
By 2100, temperatures could be about 6.7 degrees warmer. Though it wouldn't occur for hundreds of years, the huge sheet of ice over Greenland could melt entirely, leading to as much as a 23-foot rise in world ocean levels, leaving many coastal cities underwater.
This 127-page draft report, obtained by USA TODAY Tuesday, could change before its official release in Copenhagen in October.
Contributing: Associated Press