Land vs sea ice melting: A crucial difference

The biannual melting of polar ice in both hemispheres has received significant media attention over the last two decades, especially after former U.S. Vice President Al Gore’s influential documentary and book “An Inconvenient Truth” on the effect of the greenhouse gas CO2 on climate change. Associated with the melting of polar ice, is the notion of rising sea levels which, according to the U.S. National Snow and Ice Data Center (NSIDC), would rise by six meters in Greenland and twenty meters in Antarctic if regional ice sheets melted. These ice sheets are glacial land ice, meaning they are not floating on water and are, therefore, not contributing to the current sea level, as is the case with sea ice.

Said sea ice, if melted, would not directly correlate with rising sea levels since its formed either simply because of freezing temperatures in winter or, in the form of ice shelves, has been pushed into the sea via glaciers and ice streams. Thus, it is already floating and will not affect sea levels. Ice sheets, however, are ice masses on mainland. Most of Greenland, about 1.7 million square kilometers, and the entire Antarctic, almost 14 million square kilometers, are covered in ice. These sheets are formed wherever the snowfall-snowmelt balance is positive, meaning that snow that in winter does not entirely melt over summer. If this takes place repeatedly over thousands of years, the weight of new snow compresses the older layers.

Since 1979, Greenland’s ice sheet has largely had a negative snow balance, as only “[a]t higher elevations, an increase in winter snow accumulation has partially offset the melt”. Melting speed increased by 30 percent and has, therefore, passed snow accumulation. These developments additionally trigger a self-enforcing, negative feedback loop: the less area is covered in ice and snow, the less sunlight will be reflected by its bright surface. Subsequently, more energy will be absorbed by landmass and seawater which further warms the planet, contributing to accelerated melting.

The state of Antarctic ice sheets is currently unclear as no trend is yet identifiable. While the aforementioned water temperature increase may have contributed to ice sheet loss in the west Antarctic, east Antarctic weather stations have measured cooler temperatures, leaving scientists without the possibility to detect a trend. Jeremy Wilkinson, senior glaciologist at British Antarctic Survey emphasises that “[t]he science is unequivocal. Arctic change is progressing rapidly and these changes will impact us all”. What is demanded is that greenhouse gas emissions see a turning point in 2020 in order to slow down the pace of climate change.

With some actions in mind, such as the 2017 U.S. withdrawal from the Paris Agreement under President Trump, pursuing this goal will be less coordinated and possibly exacerbated. Potential economic disadvantages were cited as reasons for the withdrawal, and initiated another negative feedback loop as president of the German auto industry lobby group argued that adhering to modern climate policies would make European heavy industry less competitive. However, interdisciplinary researchers at Oxford’s Institute for New Economic Thinking are challenging this notion by offering more precise models that may incentivise companies to comply with new climate change policies while maintaining their competitive advantage.

Edited by: Patrick Lehner