What will happen to the Greenland ice sheet if we miss our global warming targets?

It’s hard to overstate how important Greenland and its mile-long ice sheet is to climate change. If all that ice melted, the sea would rise about seven meters, the height of the house.

But what happens if we can’t limit warming to 1.5C (as seems more likely)? And what happens if we manage to correct that “overshoot” and bring the temperature back? A team of researchers writes in the journal Nature has now published a study that examines these questions.

In short, their work shows a worst-case scenario of ice sheet collapse and consequent sea level rise that can be avoided and even partially reversed if we manage to reduce projected global temperatures after 2100. Furthermore, the lower and sooner those temperatures drop, the more opportunities there are to minimize ice melt and sea level rise.

We already know that the Greenland ice sheet is losing more than 300 billion cubic meters of ice a year, currently raising global sea levels by a little less than a millimeter a year. One major concern is that further warming could cross critical thresholds, sometimes called “tipping points.” For example, as the air warms, more ice will melt, which will lower the height of the ice surface and therefore expose it to warmer air temperatures and melt more even without continued atmospheric warming.

Although much more complex and nuanced in reality, it is such feedback processes that dictate that global warming be limited to 1.5 C above pre-industrial levels to avoid catastrophes such as large-scale ice sheet collapse.

How to simulate a huge ice sheet on the computer

It is critical that we can predict how the Greenland Ice Sheet will respond to future warming. To achieve this, researchers mainly use computer models of ice movement. Essentially, they divide the ice sheet into tens of thousands of 3D segments and apply the physical laws of ice motion to calculate how each segment changes over thousands of individual time steps, taking into account things like expected climate changes, ice thickness, ice slope and ice interior and ice base temperatures.

However, these projections are subject to significant uncertainties. It’s hard to know exactly how the ice is moving across the bedrock or what its internal temperature might be. And the climate is made up of many moving parts. Atmospheric and oceanic circulation may also change radically over the thousands or tens of thousands of years it takes for the ice sheet to settle into a new equilibrium.

In the face of such challenges, a group of researchers led by Nils Bochov of the Arctic University of Norway has published their new research. They ran two independent state-of-the-art computer programs that were able to model how the Greenland ice sheet would respond to different possible levels of global warming over tens of thousands of years. To simulate the consequences of exceeding the critical 1.5C threshold, they involve a gradual warming trajectory to a ‘peak’ temperature, followed by a period during which temperatures stabilize to a generally lower final ‘convergence temperature’.

Good news and bad news

The results are fascinating. If temperatures rise by 2C or more, and stay there, models predict significant ice sheet collapse in a few thousand years.

However, things change if warming is seriously moderated after 2100. In those models, the inertia of the ice sheet response is somewhat similar to the time it takes for a wave to settle over a pond, meaning that the overshoot is at least partially reversible as long as the temperature drops rapidly.

For example, if temperatures stabilize at less than 1.5C of warming by 2200, the ice sheet should remain smaller than at present, but stable. This is the case regardless of how much (mostly) peak temperatures exceed 1.5 C by 2100. In such cases, sea rise is likely to be limited to a meter or more.

However, such recovery becomes impossible if the temperature takes too long to drop or if the convergence temperature remains too high. In those scenarios, ice sheet collapse and significant sea level rise become inevitable.

Perhaps the worst can be avoided if we continue to work to reduce global temperatures in this century and into the next. Although somewhat encouraging, these predictions are subject to substantial uncertainty and much work remains to be done. In this regard, the authors are careful to note that their results are not necessarily concrete predictions, but rather provide insight into possible pathways.

This article is reprinted from The Conversation under a Creative Commons license. Read the original article.