Billions of tonnes of meltwater flowing into the world's oceans from the Greenland and Antarctic ice sheets could boost extreme weather and destabilize regional climate within a matter of decades, researchers said Wednesday, February 6. Meltwater from the Greenland ice sheet will slow the Atlantic Meridional Overturning Circulation (AMOC), the system of ocean currents that drives the climate and controls the well-known Gulf Stream.
They found meltwater from the Antarctic ice sheet will also trap warm water beneath the surface that will lead to more ice loss from the continent.
"According to our models, this melt water will cause significant disruption to ocean currents and change climate around the world".
Most studies on ice sheets have focused on how quickly they might shrink due to global warming, and how much global temperatures can rise before their disintegration - whether over centuries or millenia - becomes inevitable, a threshold known as a "tipping point".
The researchers then determined how the meltwater might affect global ocean and climate patterns.
"With this level of warming, a significant amount of melt water from the Greenland and Antarctic Ice Sheets will enter Earth's oceans", he says.
This is a "much shorter timescale than expected", commented Helene Seroussi, a researcher in the Sea Level and Ice Group at the Jet Propulsion Laboratory in California, who was not involved in the study. The team took advantage of measurements taken by satellite of ice sheet changes over the last 40 years.
"A lot of people will have heard of the Gulf Stream, this warm current that brings a lot of heat from the Gulf of Mexico up the East Coast of the U.S., into the higher latitudes and across north-west Europe". Greenland, if it were to melt entirely, would raise the global oceans level by 7 meters, while Antarctica, in case it dissolves completely, would increase sea levels by 58 meters.
Besides Greenland, the regions most vulnerable to global warming are West Antarctica and several huge glaciers in East Antarctica, which is far larger and more stable. Removing this mechanism from the model, they predict that there is only a five percent chance that the Antarctic contribution to sea level rise will exceed 39 cm by 2100 - much lower than the previous predictions of over a metre.
That would be enough to displace up to 187 million people around the world, especially in populous low-lying river deltas in Asia and Africa, research has shown.
The study calls for global government policy to be urgently reviewed to prevent risky consequences, a statement on New Zealand's GNS website said on Thursday. A study published today in Nature is the first to simulate the effects, under current climate policies, that the two melting ice sheets will have on ocean temperatures and circulation patterns as well as on air temperatures by the year 2100.
"So in this case it means the greatest sea level rise will be in the central Pacific area so a lot of those south-west Pacifica islands, Hawaii in the U.S. side of the Pacific, they're going to be experiencing nearly one and a half times the global average in terms of sea level rise so that's really important for those nations to take that on board". Overall, both papers agree that the most likely Antarctic contribution to sea level rise will be around 14 - 15 centimetres under conditions of very high greenhouse gas concentrations.