Melting of Greenland ice exacerbates rate of global sea level rise by 50 per cent

By summing up all sea-level contributions— from ocean warming to melting glaciers, a recent study has found that the rate of global sea-level rise has increased by 50 per cent over the past two decades.

Scientists estimate that sea-levels will continue to rise if the effects of climate change are not mitigated. 

The study was conducted by researchers from the CSIRO, the University of New South Wales, the University of Tasmania, as well the Ocean University of China.

Curiously, despite indications that the melting of glaciers and ice sheets were contributing to sea-level rises, there had been no reported increases in sea level observations by satellite altimery (an instrument for measuring height or altitude). 

When comparing and carefully analysing satellite and coastal measurements of sea level, they revealed a small but significant bias in satellite measurements between 1993 and 2003.

Biases ranged from conflicts owing to the differing observational techniques and different data quality control procedures and mapping methods.

In comparing the corrected satellite data from 1993 to 2014 with the contributing factors to sea-level rises over these two decades including ocean warming, the melting of glaciers and ice sheets and the amount of water stored on land, it became clear that there was an increased rate of sea level rise over the entire two decades. 

Based on corrected satellite altimetry, the rate of sea level rise went from 2.4 mm per year in 1993 to 2.9 mm per year in 2014, meaning there was a steady increase of about 0.5 mm per year from 1993 to 2014.

Ocean expansion as a result of ocean warming was pinpointed as the number one factor behind the sea-level rises, while glaciers and ice sheets were the second largest contributor. 

"Strikingly, the largest increase came from the Greenland ice sheet, as a result of both increased surface melting and increased flow of ice into the ocean," the scientists told The Conversation

Greenland's contribution to the sea-level rises increased from 5 per cent in 1993, to 25 per cent in 2014. 

"While the rate of ocean thermal expansion has remained steady since 1993, the contributions from glaciers and ice sheets have increased markedly," they said. 

The research points to the need for correction of biases in earlier data to understand the rapid rate of sea-level rises, while also demonstrating the need for effective climate change protocols. 

"If the global community fails to move toward zero greenhouse gas emissions very soon then the planet will see something like 1 metre of sea level rise by 2100," Matt King, a professor in Surveying & Spatial Sciences who was involved in the study, told Australian Geographic. 

"Recent studies have suggested Antarctica could contribute more than previously thought – if this occurs, then sea levels will rise by more than 1 metre by 2100. We can limit the damage but we can also make it worse. This rise will affect coastlines but more than that will have effects on human migration and, potentially, national security."

Matt explains that considering $250 billion of Australian infrastructure sits within 1.1 metre of sea level, building new flood defences may help in some locations, however these are expensive.

"For many locations, planned retreat from vulnerable coastlines needs to be considered well in advance – this will affect private landowners, businesses and governments."

The research was published in the journal Nature Climate Change.

Source: Australian Geographic.