For the past few decades, climate scientists have been facing something of a mystery. Sea levels did not appear to be rising as rapidly as models predicted, which was puzzling because the world’s ice caps and glaciers were melting at a faster rate than originally expected. It would be a bit like watching water flow into a bathtub without seeing the water level rise.
Now new research led by a team at the University of Tasmania and published in the journal Nature Climate Change appears to shed light on the mystery.
The satellite era describes the period from 1993 to 2014 or the period during which scientists relied heavily on satellite data to gauge sea level rise. According to Dr. Christopher Watson from the University of Tasmania’s School of Land and Food, the reliability of that satellite data is crucial.
“This information is vital as communities around the world plan and respond to our changing climate. Previously, it was clear that the rate of rise over the past 20 years was roughly double the rate determined over the past century – what was curious was that the rate appeared slower in the last decade relative to the one before. That slowing has puzzled scientists because it coincides with an increase in water entering our oceans from Greenland and West Antarctica,” said Dr Watson in a statement.
Dr Watson’s team, along with Australia’s Commonwealth Scientific and Industrial Research Organisation (CSIRO) used GPS measurements of land movement along with tide gauge data to refine the way the satellite data was being read.
They found that seas have risen faster since 1993 compared to previous decades. They also showed that, allowing for the new corrections, the first six years of satellite data slightly overestimated the trend toward sea level increases. The increase during that period was 2.6 to 2.9 mm annually compared to a previous estimate of 3.2 mm.
The research shows that the rate of sea level rise has increased during the satellite era. However, fluctuations in the rate of increase occur because of the movement of water between land and sea. Events such as floods which saturate the land with water can have a small impact on the rate of sea level increase.
“Unlike the previous slowing, an estimate of acceleration is striking in that it is consistent with the projections of future sea level published by the Intergovernmental Panel on Climate Change,” said Dr Watson.
According to CSIRO’s Dr John Church current estimates show a global sea level rise of 38 inches by 2100 if greenhouse gas emissions continue to climb at their current rate.
“The projections reduce to a rise of between 28 and 61 cm if we follow paths that include very stringent mitigation of global emissions. Rising sea levels will place increasing stress on the coastal zone – inundation events will become more frequent and adaptation will need to occur. Agencies need to consider the impacts of accelerating sea levels and provide communities with advice and planning directions that are commensurate with the magnitude of the problem,” said Dr Watson.
Estimated levels of sea level rise could increase in coming years if the rate of glacial melting continues to accelerate beyond predicted levels and as new discoveries are made.
In March, researchers from the University of Texas at Austin found what appears to be flowing water moving beneath Antarctica’s massive Totten Glacier.
“Now we know the ocean is melting ice in an area of the glacier that we thought was totally cut off before. Knowing this will improve predictions of ice melt and the timing of future glacier retreat,” said PHD candidate Jamin Greenbaum at the time.
