Kristine Wong is a regular contributor to TakePart and a multimedia journalist who reports on energy, the environment, sustainable business, and food.

A new study has found that the world’s existing fossil fuel power plants will spew more than 300 billion tons of carbon dioxide into the atmosphere over their four-decade life span.

That’s more than 20 percent of the Earth’s carbon budget of 1,400 billion tons—the highest level of carbon dioxide that scientists believe can be emitted and not raise the global temperature beyond the threshold of 2 degrees Celsius agreed to at the 2009 United Nations climate talks in Copenhagen.

It may seem strange that nobody thought to count this before, but the study is the first worldwide tally of carbon emissions from power plants by accounting for future emissions, also known as committed emissions.

“Our study shows that despite international efforts to reduce CO₂ emissions, total remaining commitments in the global power sector have not declined in a single year since 1950 and are growing rapidly—by an average of 4 percent per year from 2000 to 2012,” said Steven Davis, an earth sciences researcher at the University of California, Irvine, and the coauthor of the paper, published this week in the journal Environmental Research Letters.

In contrast, annual carbon emissions from existing power plants grew by 3 percent over the same period, meaning the world is still building more fossil fuel power plants than it’s mothballing.

Here’s an example of this differential: While the power plants built in 2012 alone are projected to release 19 billion tons of carbon over their 40-year lifetime, the CO₂ emissions that year from all the power plants already operating at that time was 14 billion tons.

“We’re taking on more debt than we’re paying, so the balance is growing—and that’s disturbing,” Davis said.

The results improve on current data used by the U.N.’s Intergovernmental Panel on Climate Change, which has incorporated estimates about the number of new power plants into their emissions scenario models, according to Davis.

Why hasn’t the analysis been done before?

“It’s a data-intensive process, and only recently has there been more access [to information],” Davis said, who used data from Platt’s, a company that collects information about the energy industry.

His research team also conducted an analysis of where new power plants are coming online. While the United States is retiring more power plants than it’s building, the European Union is bringing them online at the same rate that it’s taking them offline, according to Davis.

“But in China, India, Indonesia, Iran, and Saudi Arabia, there’s been a lot of coal-fired power plants—it’s been as high as four times more commitments in any given year versus what they’re emitting right now,” he said. “That’s like charging $400 [on a credit card] in any given month and only paying $100.”

But since 2010, China has slowed construction of coal-fired power plants, while Southeast Asia has been building more to expand its industrial capacity, Davis noted.

He is working on estimating future emissions from the power plants that came online in 2013, noting that such a tally should be done annually to incorporate the latest data available.

In the meantime, his 2012 results have gotten the attention of IPCC scientists in Vienna, with whom he’ll be collaborating to develop a new carbon emissions scenario based on his findings. Davis has also been in contact with the U.S. State Department about the results.

In December, he’ll be presenting at the next U.N. climate talks, which are scheduled to take place in Lima, Peru.

“I’d say these commitments are growing so rapidly that they’re in line with that worst-case emissions scenario presented by the IPCC,” he said, referring to a world where carbon emissions continue to grow past the year 2100.