What Does the Future Hold?

The Antarctic's response to recent climate change is complex: the West has warmed and experienced significant ice shelf melting,  affecting its overall stability. On the other hand, the East has cooled in places and remained comparatively stable. What does the future hold for the icy continent?

Tipping points

Before we examine future projections let's touch briefly on a key concept for ice sheet stability: tipping points.

A tipping point describes the critical threshold at which the system switches from one stable state to another; it may be irreversible. Current knowledge about climatic tipping points is poor and estimations of Antarctic collapse uncertain. However, if certain thresholds are met they could trigger extensive sea level rise and ecological change. 

It's getting hot in here!

Evidence from paleoclimatic data indicates that there is a linear relationship between global temperatures and Antarctic ice accumulation. As temperatures continue to rise, it is likely that Antarctica will shrink. However there are uncertainties attached to this estimation.

At present the East Antarctic Ice Sheet (EAIS) is relatively stable and is expanding in some places. Current evidence shows that the warmer air can hold more moisture, contributing to ice sheet growth. However, Fogwill et al., 2014 suggest that climate change may threaten weaker sections of the ice sheet, which would trigger accelerated mass loss. 

A recent study modelled the effects of continued climatic changes on the stability of the West Antarctic Ice Sheet (WAIS). The findings suggest that the current retreat of peripheral ice shelves would continue under a warming climate. In fact, Gollege et al., 2015 predict that the stability of West Antarctic ice shelves is dependent on two critical temperature thresholds: 0.5°C  of prolonged ocean warming coupled with atmospheric warming of 2°C would result in 80-85% losses of the floating ice around Antarctica. These ice shelves are key for WAIS stability, so a crossing of these thresholds could lead to runaway melt and eventual ice sheet collapse. Arguably, the WAIS is poised to reach a tipping point. 

Modelled changes of Antarctica under the RCP warming scenarios for 2100 (a, d, g, j) , 2300 (b, e, h, k) and 5000 (c, f, i, l). Grey areas show fast flowing ice and light blue areas show high grounded ice loss. The magnitudes and rates of sea level rise are shown in each box (Image: Gollege et al., 2015). 

Why does it matter?

Sea levels were between 6 and 9.3m higher during the Last Interglacial (which occurred between 130 and 115 kyr) and global temperatures were only 0-2 °C warmer than they are today. These high sea levels have been partly attributed to Antarctic melt. 

Using the IPCC's Representative Carbon Pathways (RCP) DeConto and Pollard, 2016 modelled the Antarctic's contribution to global mean sea levels (GMSL) under different emission scenarios:  

1.  RCP2.6 produces a negligible contribution to GMSLs by 2100 and 20cm by 2500. 
2. RCP4.5 would lead to 32cm of rise by 2100 but, worryingly, would cause the WAIS to collapse by 2500 and result in a scary 5m of GMSL rise!

Antarctic contribution to GMSL under RCP scenarios. GMSL by 2100 (a) and by 2500 (b) (Image: Pollard and DeConto, 2015)

Similarly, Bamber et al., 2009 estimated that collapse of the WAIS alone could cause global eustatic sea level rise of 3.3m, with regional variations. Specifically, projections suggest that peak increases in sea level would be focused around the Pacific and Atlantic sides of America. However, projections about sea level rise from the collapse of the WAIS are inherently surrounded by uncertainty in the input data and system behaviours.

The future is uncertain 

Projecting Antarctica's response to future climate change and modelling GMSL is difficult, and inherently uncertain. Firstly, it is not known how global emissions may change in the future. Consequently, studies that use the RCP pathways are particularly useful as they give a range of projections. Secondly, there is parametric uncertainty in the models: complex processes are simplified (including ice and ocean dynamics) so outputs should be interpreted as ranges of possible responses rather than certain projections. Finally, the equilibrium response for ice sheets is longer than that of the atmosphere or oceans, making it difficult to provide a timescale for GMSL change.