Greenland Ice Sheet Tipping Points

The goal of the ARIA Forecasting Tipping Points programme is to “To create an early warning system for tipping points that equips the world with the information we need to build resilience and accelerate proactive climate adaptation.” – Read the programme thesis here.

What are “tipping points”?

Imagine that you are sitting in dry clothes in a canoe in a swimming pool and you rock from side to side. The canoe is stable and so it will return to its original position if you rock it gently. However, if you rock it harder and harder, eventually the canoe will tip you into the pool. You can’t return back to your original stable state – because your clothes are now wet! The point at which your canoe rocks past the point from which it can return to the original state is the tipping point.

In the same way, a climate tipping point is a point at which the perturbation of a particular aspect of the climate system is large enough that the climate enters a completely new regime – once a climate tipping point is passed, there is no easy way to return back to the original state of the system. Therefore understanding what perturbations might result in the crossing of a climate tipping point, when they might occur, and what the new regime might look like, is critical for us as a society to be resilient to potentially rapid climate change.

Why Greenland?

The Greenland Ice Sheet (GrIS) is an example of a system with a potentially impactful ‘climate tipping point’. With a volume of more than 2 million km3, the GrIS is the largest single mass of ice in the Northern Hemisphere, and the water contained within it is equivalent to more than 7 m of global sea level rise.

This mass of ice is so large, it is partly responsible for driving its own climate- the high altitude of the central GrIS means that the air temperature is colder, resulting in precipitation falling as snow, and the bright colour of that snow reflects more solar radiation, keeping the ice sheet cold and maintaining the high elevation. This gives the GrIS a degree of stable inertia – small changes to the climate (for example air temperature or precipitation amount) do not make a big difference to the long-term mass of the Greenland Ice Sheet.

However, as global temperatures increase and weather patterns change in response to increasing levels of carbon dioxide in the atmosphere, the Greenland Ice Sheet will reach a point where it becomes unstable, and the processes that once kept it constant now cause positive feedback loops that accelerate it into a ‘new stable state’. One example might be that air temperature becomes sufficiently warm that it rains on the ice sheet where it used to snow, the rain causes the ice to darken, which causes it to absorb more solar radiation, accelerating surface melt. This could cause a ‘runaway melt’ event, where the GrIS continues to melt even if the initial perturbation (changing temperature for example) returns to how it was before the tipping point was crossed.

Crossing a tipping point beyond which the GrIS will lose a large amount of mass will have far-reaching consequences. For example, the resulting increase in sea-level will threaten coastal communities globally, and the increase in run-off and retreating ice will impact local communities and eco-systems. A massive reduction in the size of the GrIS could also have knock-on effects for other climate processes (and potentially drive other climate tipping points) such as modification of the North Atlantic Storm track, subpolar gyre, and the Atlantic Meridional Overturning circulation.

Despite the potential consequence of crossing a GrIS tipping point, identifying when and how that tipping point is crossed (or even if it already has been) is extremely challenging, which is why ARIA have identified it as a research priority.  

Where does GAMB2LE come in?

To understand when and how a GrIS tipping point might be crossed, we need to be able to accurately monitor environmental conditions on the ice sheet: from sub-surface ice dynamics and meltwater percolation, to the energy and mass balance at the ice-atmosphere interface, to the weather at climate over the ice sheet. We also need to be able to understand the spatial variability of these processes across the whole ice sheet, and the temporal variability across the scales from days to centuries. To address this challenge, we need multiple ways to monitor the ice sheet; we need satellite observations to the vast spatial area, we need surface-based measurements that aren’t impeded by clouds and the atmosphere, and we need models to fill the gaps where our observations can’t reach.

Currently, surface-based measurements of the ice-atmosphere interface and weather and climate variables are available from small low-powered weather and ice sheet monitoring stations or from large manned research stations. Small autonomous stations can capture the spatial variability of key parameters, but they are necessarily limited in scope due to the harsh environmental conditions and low power requirements. Large research stations can collect a large wealth of data but are limited to a small number of locations and have large environmental footprints.

The objective of GAMB2LE is to bridge this gap in surface observations by capitalising on recent advances in renewable technology and automation to build an advanced polar observatory with the measurement capability approaching that of a manned station, but the environmental footprint and deployability akin to that of a small weather autonomous weather station (see Arctic-hardened mobile Observatory).

We will use this new observatory, known as the Automated Unit for Remote Observations and Research of the Atmosphere (AURORA), to generate state-of-the-art data products in near real time that will allow us to understand the complex processes interacting to drive the surface energy and mass budgets of the ice sheet at key locations on the ice sheet. These data will feed into efforts to understand Greenland Ice Sheet tipping points.