Antarctic Ice Thinning - a Literature Review

Antarctic ice thinning out – increasing rates set to change the world

ABSTRACT

The cryosphere is of vital importance to the planet, not only for the large amount of freshwater it holds but also for its impacts on global climate. Yet just as the cryosphere can influence climate, changes in the atmosphere too can dramatically alter ice and snow in places like Antarctica (Bamber & Payne 2004). It has been noted across various Antarctic studies that the continent is changing both faster and sooner than predicted by climate models (Joughin et al. 2011; McMillan et al. 2014; Mengel & Levermann 2014). Antarctica’s Western region appears to be the area of highest concern among climate scientists. Glaciers in this area are retreating the fastest (Rignot et al. 2014) and their corresponding effects on sea level are expected increase as ice sheets melt (McMillan et al. 2014). Rising sea level figures tend to predict a range between 0.52-0.98 metres before 2100. However, results remain speculative amongst the scientific community as they are all based on different model and data simulations. This literature review brings together all the independent evidence for Antarctic changes in order to determine how and when Antarctic ice melt will affect global sea level.

Keywords: climate change; rising sea levels; global; ice loss; warming

INTRODUCTION

 The Earth’s cryosphere is fundamental to the planet. Ice and snow reflect the sunlight that regulates our planet’s habitable temperature (Goodstein et al. 2010). Unfortunately, the cryosphere is particularly sensitive to anthropogenic disturbances. In recent years, Antarctica has begun to show visible signatures of climate change as ice sheets melt into the ocean. The latest Intergovernmental Panel on Climate Change (IPCC) report has projected sea level rises to occur within the century, which will have massive socioeconomic implications on the world (Vaughan & Comiso 2013). Thus, understanding the climate change in places like Antarctica is important on a global scale. Many research papers studying Antarctica have found evidence supporting rising sea levels (McMillan et al. 2014; Mengel & Levermann 2014; Rignot et al. 2014)  while others identify new tipping points for the climate such as degrading permafrost (Guglielmin 2011) and rising temperature (Steig et al. 2009).  Climate change predictions are varied but all seem almost apocalyptic in their implications. Hence, the primary objective of this literature review is to discuss both how much and when Antarctic ice sheets will change global sea level. It is likely that updated research will show increases in climate changes occurring sooner than previously expected.

ICE SHEET STABILITY

For much of the 1990s the scientific community believed Antarctica’s ice sheets would remain relatively stable in the face of climate change. Even if the ice sheets were to retreat, it was projected on timescales of over hundreds or thousands of years (Ding et al. 2001). Now, in 2014, it is clear climate change is having a discernible effect - reductions in ice volumes are occurring at a rate faster than expected (Mengel & Levermann 2014; Rignot et al. 2014).  Indeed, the current acceleration of ice sheet melting means not only will ice sheets become the dominant cause of sea level rise but also exceed the IPCC contribution estimates  (Rignot et al. 2011). Recent image analyses taken from the Cryosat-2 radar altimeter, a European Space Agency satellite, recorded 159 billion tonnes of ice disappearing from the continent each year (McMillan et al. 2014). In conjunction with satellite imagery, new ice and climate models like the Gravity Recovery and Climate Experiment (GRACE), are finding reductions in both the extent and magnitude of ice-shelf thickness (Gunter et al. 2014).

Yet despite all the independent evidence for ice sheet thinning, ice thickness dynamics remain poorly understood. Atmospheric temperatures, sublimation rates, basal melt and glaciation cycles all contribute in some way to the melting of ice sheets. It is often difficult for climate models and ice sheet studies to take the myriad of factors into account and, consequently, the total ice sheet contribution to sea level rise remains speculative. Indeed, the main cause of melting is still debatable. Is it mostly attributable atmospheric warming by found by studies like Steig et al. (2009) or oceanic warming from circumpolar currents found by Dinniman et al. (2011)? Recent research by Pitrichard et al. (2012) may provide an answer. The study by Pitrichard et al. (2012), which examined ice shelves (extension of ice sheet over water), found that wind influences both basal melting and the surface melting.  ‘Wind forcing’ appears to be the cause of an increased supply of warm oceanic water that is thinning the  West Antarctic ice sheet (WAIS), and the cause of atmospheric warming that triggered the collapse of  Larsen A and B ice shelves. Thus, it seems that ice-sheet mass balance is influenced from both above and below its surface. More importantly, however, both melting processes are ultimately linked to the atmosphere, which means it is even more important to recognise the effects of anthropogenic pollution.

CONCERNS FOR WEST ANTARCTICA

West Antarctica, which holds enough water to raise sea level by six metres globally, has long been recognised as an area vulnerable to climatic change (Oppenheimer1998). Over a decade ago the IPCC considered the collapse of WAIS as ‘high risk, low probability’ (Ding et al. 2001). The probability has since increased as the WAIS’s unique environment has given rise to theories of potential collapse (Bindschadler 2006).  The WAIS is situated in a warm, marine geologic basin, which makes it unlike any other ice sheet left on the planet. Beneath the ice shelf warm ocean waters flow well into its interior, which is highly concerning as a study conducted by Steig et al. (2009) found temperatures to be on the rise.