Melting ice sheets may alter our weather while raising sea levels

Sea level rise isn't the only thing we have to worry about as the Greenland and Antarctic ice sheets melt. A new modeling study finds that runoff from these ice sheets could significantly alter crucial ocean currents in ways that disrupt the Gulf Stream and accelerate ice loss in West Antarctica.

Why it matters: The study, published in the journal Nature on Wednesday, shows the potentially far-reaching ramifications of ice melt.

The big picture: Scientists are racing to better understand and anticipate the pace, extent and impacts of melting glaciers, both in Greenland and Antarctica. Since the last report from the UN Intergovernmental Panel on Climate Change in 2014, sea level rise estimates have increased, but uncertainties remain high.

• The new study, by a group of researchers from New Zealand, Canada, Germany and the U.K., is one of the first to pair a climate model with an ice sheet model — fed with the latest observational data on ice loss — to see how ice melt might alter the planet's climate.
• It finds that the influences may be profound.

The threat: If the Greenland or Antarctic ice sheets melt quickly and significantly enough, they could pour enough cold, relatively light freshwater into adjacent areas of the ocean to disrupt global ocean circulation, the study finds.

• In particular, the study adds to the growing concern in the scientific community about a slowdown in a current known as the Atlantic-Meridional Overturning Circulation, or AMOC.
• This current is also referred to as a global conveyor belt or global thermohaline circulation, carrying heat and oxygen from the bottom of the world to the far north, and back again.
• There are clear signs that part of this current is already slowing down, due to freshwater inputs from Greenland.

The new study says this could lessen the heat transported to Europe and may make weather more variable in the northeastern U.S., among many other areas. Worse yet, in the Antarctic, adding freshwater to the surface ocean would serve to reduce the amount of mixing between ocean layers, the study says.

• This would trap salty and warm water well below a film of cool, freshwater on the surface.
• Such warm, salty waters are melting marine-terminating glaciers in West Antarctica by eating away at their floating ice shelves and infiltrating the ice bed in areas where the bedrock is below sea level.

What they're not saying: The study assumes that the ocean is not playing a large role in melting Greenland's glaciers, which is at odds with observations, according to Eric Rignot, a professor of Earth system science at UC Irvine, who was not involved in the new study.

• Rignot says Greenland will melt faster and more extensively than the study's models show.

What they're saying: Luke Trusel, a study coauthor and geology professor at Rowan University, told Axios that melting ice sheets will have effects far beyond sea level rise.

"Ice sheets aren't passive bodies of ice, they're dynamic, interactive components of the Earth system. They change in response to climate, and climate then responds to their change."

"'Melting ice sheets don't just cause sea level rise. They also disrupt the climate system, by dumping a lot of cold freshwater into the ocean," says study coauthor Kaitlin Naughten of the British Antarctic Survey, in an email to Axios. "This affects deep ocean circulation, surface ocean currents, and weather patterns across the globe."

Go deeper:

• Greenland Ice Sheet melting at unprecedented rate in past 350 years or more
• Scientists find new evidence of life beneath Antarctic ice
• Antarctica is losing ice 6 times faster than in 1980s