The widespread loss of forests in the tropics means the region emits more carbon than it captures, reversing its longtime role as a safeguard against climate change, researchers said Thursday.

The analysis in the journal Science relies on 12 years (2003-2014) of satellite imagery, laser remote sensing technology and field measurements.

This approach allowed scientists to focus on aspects of forest loss that were previously hard to measure, such as small-scale tree removal and mortality, also known as forest degradation.

Most of the carbon emissions from forests -- making up nearly 70 percent in the tropics of the Americas, Asia and Africa -- are linked to forest degradation, said the report.

"Deforestation, degradation and disturbance has caused tropical forests to now emit more carbon than they capture, countering their role as a net carbon 'sink,'" it said.

Prior studies have tended to focus on carbon loss from areas subject to complete forest removal, or deforestation.

"These findings provide the world with a wakeup call on forests," said lead author Alessandro Baccini, Woods Hole Research Center scientist.

"If we're to keep global temperatures from rising to dangerous levels, we need to drastically reduce emissions and greatly increase forests' ability to absorb and store carbon."

The study found that tropical regions are a net source of carbon to the atmosphere -- putting out about 425 teragrams of carbon annually, more than the emissions from all cars and trucks in the United States.

"Gross annual losses were about 862 teragrams of carbon and while gains were approximately 437 teragrams of carbon," said the report.

Most of the forest loss -- almost 60 percent -- has occurred in Latin America, which is home to the Amazon.

About 24 percent of the loss is attributable to Africa.

The forests of Asia experienced the least losses -- just over 16 percent of the total for the tropics.