Global warming is fueled by human activities, it's escalating quickly and some of its worst effects are probably irreversible. Those are the grim conclusions in a leaked draft of a major new United Nations report on climate change, scheduled to be formally released in early November.

"Human influence has been detected in warming of the atmosphere and the ocean, in changes in the global water cycle, in reduction in snow and ice, and in global mean-sea-level rise; and it is extremely likely to have been the dominant cause of the observed warming since the mid-20th century," the unfinished 127-page draft states, as reported by the New York Times. "The risk of abrupt and irreversible change increases as the magnitude of the warming increases."

Earth's overall warmth is on a long-term surge alongside man-made greenhouse gas emissions, namely carbon dioxide (CO2) from burning fossil fuels. Vital to life at lower concentrations, atmospheric CO2 is now reaching levels unseen in human history. It hit 400 parts per million in 2013 for the first time since the Pliocene Epoch, and then in 2014 it averaged 400 ppm for a full month.

The last time Earth's CO2 levels were this high, its surface was roughly 11 degrees Fahrenheit warmer and sea levels were 100 feet higher. Global temperatures are projected to rise by up to 7 degrees Fahrenheit over the next 80 years, based on current emissions rates, and oceans have already risen 8 inches over the past century. They could rise 3 feet more by 2100, adding to other effects of climate change such as longer droughts, fiercer wildfires, more strong storms and less food security.

The draft was produced by the U.N. Intergovernmental Panel on Climate Change (IPCC), a Nobel-winning group of scientists whose climate reports summarize research from around the planet. It doesn't reveal a lot that hasn't already been reported by the IPCC, but it does use more dire wording than previous updates. It was sent out to world leaders this week for review, and that's apparently when it was leaked. The final report may therefore undergo revisions before its official release.

This leak comes amid rare hints of progress in the international fight against climate change. In June, the Obama administration unveiled a proposal for the first U.S. limits on CO2 from existing power plants, following recent restrictions on newly built plants as well as fuel efficiency standards for new cars and trucks. U.S. CO2 emissions are already at a 20-year low, but they're still unsustainably high — and U.S. policy updates like these are a key step in negotiations with China and India.

The U.N. will host a climate summit in New York next month, although it's not part of formal U.N. climate talks. Those continue in Lima this December, leading up to a major Paris summit in December 2015. There, the U.S. is reportedly planning to push for a "pledge-and-review" treaty that would rely on political pressure to curb CO2 emissions rather than elusive legal requirements.

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