Steam billows from the cooling towers of a brown-coal power station behind wind turbines. Promises to sharply reduce carbon emissions aren’t enough to prevent global warming, a U.N. study says. (Pawel Kopczynski/Reuters)

Pledges by the United States and other countries to sharply reduce greenhouse-gas emissions still aren’t enough to prevent global temperatures from rising beyond levels that scientists believe could be dangerous to the planet’s health, a U.N.-commissioned study says.

The report by the United Nations Environmental Program (UNEP) cited a sizable “emissions gap” between the promises made by world leaders to lower pollution and the maximum amount of carbon the atmosphere can safely absorb.

“Without additional climate policies, global emissions will increase hugely up to at least 2050,” said the study, released Wednesday by the U.N. body that established the Intergovernmental Panel on Climate Change, the scientific organization that studies the effects of heat-trapping greenhouse gases on the global environment.

But the study also argues that nations could eliminate the gap by ramping up investments in renewable energy and making smarter policy decisions on economic development.

“On the one hand, we’re way off track. But on the other hand, there is increasing evidence that much of this can be done more cheaply than has previous been estimated,” said Andrew Steer, president of the World Resources Institute, a Washington think tank that provided technical support for the study.

Current pledges to reduce greenhouse gases aren't enough to prevent dire consequences by the end of the century. (The Washington Post/Source:)

Citing warnings from climate scientists, world leaders agreed four years ago to a goal of limiting the rise in global temperatures from greenhouse gases to no more than 2 degrees Celsius, or 3.6 degrees Fahrenheit. But carbon emissions have continued to soar, making that goal harder to achieve.

To stay below a 2-degree temperature rise, nations will have to achieve “global carbon neutrality”— meaning no net increase in the amount of carbon in the atmosphere — sometime in the second half of the century, the report said. For that to happen, countries will have to rapidly shift to cleaner forms of energy while also creating new carbon “sinks,” such as expanded forest cover, to draw carbon dioxide out of the atmosphere.

Under current projections, the study said, the growth of global carbon emissions will have to peak within the next decade and fall by half by 2050 to meet the 2-degree goal.

“Taking more action now reduces the need for more extreme action later to stay within safe emission limits,” said Achim Steiner, UNEP executive director.

The release of the report comes a week after China and the United States announced historic pledges to scale back carbon emissions in the next two decades. U.N. officials hailed the agreement at the time as a breakthrough but said the U.S. and Chinese pledges alone would not be enough.

“There is a lot of bottom-up climate action going on, but the question is: Does it add up to climate protection?” said Joseph Alcamo, UNEP’s chief scientist.

Related: U.S. and Chinese officials found common ground on climate

A computer model tracked the movement of Earth's carbon dioxide for one year. (NASA)