As the biggest single chunk of melting ice and snow in the world, Greenland's massive ice sheet is considered to be potentially the biggest contributor to rising sea levels, no thanks to the amount of meltwater it produces.

Scientists, however, have mostly been focusing on the ice sheets' bodies of meltwater, which have the tendency to drain abruptly, and the huge chunks of ice sliding into the ocean that turn into icebergs. A team led by researchers from the University of California, Los Angeles explored the vast network of streams and rivers on top of the ice sheet and have discovered that these could lead to at least the same, if not higher, increase in sea level as the two other sources combined.

In a study published in the Proceedings of the National Academy of Sciences, the researchers detailed that the network of streams and rivers turn into an intricate drainage system that catches all surface runoff when ice and snow thaw during the summer. At the same time, the network is capable of flushing out all the water it has caught in under two days.

Laurence Smith and colleagues measured conditions in the ice sheet in 2012 using military-grade satellite imagery, GPS buoys and a drone boat. To get around the area, the researchers relied on a helicopter. Their time in Greenland coincided with a massive melt, giving them a preview of how quickly the ice sheet could melt and the rate at which meltwater could drain.

The researchers found that the ice sheet was both capable of carrying meltwater into the ocean and moderately absorbing some of the drainage.

A closer look as well at the Isortoq River, which drains a fifth of the network on top of the ice sheet, revealed that some of the water it drains is unaccounted for. This can be problematic given the river is used on the Modele Atmospherique Regional, a climate model utilized by the Intergovernmental Panel on Climate Change in developing international responses to global warming. Specifically, there was a 25 percent discrepancy between data from the researchers and the climate model's predictions, with researchers logging in less.

"The model automatically assumes that the meltwater is going directly to the ocean. Some can be retained under the ice. More research is definitely needed," said Marco Tedesco, Cryospheric Processes Laboratory head at the City College of New York and co-author for the study.

Tedesco explained getting better estimates would lead to better projections that would ultimately affect response to global warming.

"Greenland is really the big player for sea level rise in the future, so improving climate models is extremely crucial," he added.