Sea level rise from melting ice caps may soon be halted

Sea level rise from melting ice caps may soon be halted

Where climate change and its various effects are widely talked about today, the conversation used to be simpler. We called it “global warming” and worried about cooking outside in the summer and rising sea levels that would claim so many of our favorite cities.

Scientists now fear that sea level rise may be stalled as ice caps and glaciers pass ‘tipping points’ beyond which their loss cannot be stopped. Research is ongoing to determine the best way to avoid these tipping points.

The threat of sea level rise from melting ice is often overlooked by climate change skeptics. The common quote is that a floating ice cube does not change the water level when it melts, due to the principle of displacement. However, this ignores the fact that much of Antarctica’s ice actually sits on land. When this ice melts, it directly leads to sea level rise of a potentially drastic magnitude.

Although the loss of floating ice does not directly cause sea level rise, there is concern that the loss of pack ice will increase the rate of melting of the Thwaites Glacier it is holding. Credit: NASA, public domain

The Thwaites Glacier, which scientists have dubbed the ‘apocalypse glacier’ for the perceived danger it poses, is the main area of ​​concern. The glacier is held back, especially to the east, by a large floating pack ice. This slows the flow of the glacier and helps keep it stable. The floating ice shelf is further aided in this task as it rests against a large undersea mountain, acting as a reinforcement.

Recently, scientists noted that the floating pack ice was showing worrying signs of deterioration. Large cracks have been cobwebbed across the ice, raising concerns about the shelf’s long-term stability. The effect is similar to cracks in a window; once they reach a certain point, the whole glass shatters. Compounding the problem, the pack ice appears to be losing its grip on the seamount holding it in place as warmer waters melt the slick from below.

When land ice rests on the ground below sea level, it can allow seawater to pass below if the ice sheet is not heavier than the denser seawater it would otherwise displace. This water then melts the ice from below at an increasing rate as the grounding line moves further inland. Credit: NASA, public domain

The Thwaites Glacier is already responsible for about 4% of global sea level rise each year. The concern is that with the loss of the floating sea ice, the glacier could increase its flows to the ocean, increasing sea level rise by up to 5% in the short term alone. Scientists currently expect the sea ice to break up in the next 5 years or so.

The longer-term implications are profound, though uncertain at this stage. If the wider Thwaites Glacier breaks up and melts, a process scientists expect could occur in just a few centuries, it would contribute to a 65 centimeter rise in global sea level. West Antarctica was lost, this would add 3.3 meters to global sea level, completely changing the world map.

We prefer frozen Greenland, not green

Many glaciers, such as the Jacobshavn Isbrae Glacier, have retreated since the industrial era. The concern is that soon their loss could be locked in regardless of future greenhouse gas emission reductions. Credit: NASA, public domain

It’s not just a problem in the southern hemisphere either. Scientists think 1-2 meters of sea level rise could be blocked by Greenland’s glaciers which look set to melt no matter what we do now. 140 years of records of ice sheet height and ice melt rates in the Jakobshavn Basin indicate that there may be a feedback effect causing rapid ice loss. As the ice cap thins, it is more exposed to warmer air at lower elevations, which hastens the effect.

Melting ice also disrupts ocean circulation. Colder waters from melting Greenland ice are slowing the currents responsible for transporting heat through oceans around the world. Fears are that this could disrupt rainfall over crucial areas, create more droughts and warm the southern oceans, further accelerating the melting of the West Antarctic ice sheet.

There is some comfort to be had in the timescale of the predicted melt, at least for humans living now. The 1-2 meter rise of the Jakobshavn melt is expected to take a few centuries to progress, although we cannot stop it now. It is also not certain that a tipping point has been passed, however, with global temperatures and greenhouse gas concentrations continuing to rise, this point may be debatable. Either way, absent a return to pre-industrial temperatures, researchers believe that significant ice loss and a corresponding rise in sea level is almost a certainty.

The most heartbreaking predictions suggest that the loss of the Greenland ice sheets could be stuck at 1.5°C of warming, which could be reached as early as 2030. If the models are correct, once that point is reached, reducing emissions and stabilizing global temperatures would not be enough to save the ice cap, which would continue to melt and slowly raise sea levels over a long period of time.

Future prospects

Taken in isolation, neither glacier poses an immediate threat to our coastal cities over the next decade. However, if multiple climate systems continue to be pushed beyond tipping points, as we have already explored, we could end up locking in significant negative changes before we can reduce emissions and stabilize the climate.

[Banner image: “Surprise Glacier” by USGS. Thumbnail: Calving at Perito Moreno by NASA Goddard.]

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