WASHINGTON (AP) — The world still isn't close to preventing what leaders call a dangerous level of man-made warming, a new United Nations report says. That's despite some nations' recent pledges to cut back on carbon dioxide emissions.

The report looks at the gap between what countries promise to do about carbon pollution and what scientists say needs to be done to prevent temperatures rising another two degrees. The two-degree level is a goal that world leaders set in 2009.

"The time window (for reaching that goal) is closing, closing," said United Nations undersecretary for environment Achim Steiner. And the cost of getting to that goal "is increasing, increasing."

To meet that goal, the world has to hit a peak of carbon dioxide, methane and other greenhouse gases before 2030, said the report's chief scientific editor, Joseph Alcamo. But the study says carbon emissions will continue to soar until 2050 and by then it will be too late.

Using basic math and science, researchers figured out how much greenhouse gas the world can emit by 2030 and keep below that two degree mark: about 46 billion tons (42 billion metric tons). Without factoring in this month's promises by the U.S. and China to reduce emissions, the world will be spewing between 15 and 19 billion tons more than that, said Alcamo, chief scientist for the United Nations' environmental arm.

If the U.S. and China follow through with their promises, they may shave a few billions of tons off the total, said former U.S. Sen. Tim Wirth, vice chairman of the United Nations Foundation. Those pledges and an earlier one by Europe, while narrowing the gap, aren't large enough to close it, Alcamo said.

In his forward to the report, Steiner wrote that the "analysis reveals a worrisome worsening trend. Continued emissions of greenhouse gases will lead to an even warmer climate and exacerbate the devastating effect of climate change."

Outside scientists praised the numbers in the study, but Granger Morgan at Carnegie Mellon University raised a question that scientists have been debating more frequently: Is it time to abandon the two-degree goal as unrealistic?

"Today a two-degree target is akin to a 60-year-old man who resolves to be 25 years old next year," Morgan said in an email. "It ain't gonna happen, but it's time to get really serious about achieving what we can."

Steiner said because of the dangers of a warmer world, it is unthinkable to abandon the two-degree goal.

After the report was released at a Washington news conference, Tommy Remengesau — president of the small island nation of Palau, which is threatened by sea level rise — told The Associated Press that this really isn't about numbers: "For some of us, it's a matter of survival: life and death."