Aug 14, 2019

The rise in the Oceans' level has accelerated since the 1960s


By 2100, the global rise could be twice the expected growth compared to a normal projection  

Rise in the Ocean level, Chile.
City of Viña del Mar, Chile
Photo: laotravoz.org

The study of the Earth by satellites revealed that the sea level of the entire planet has been growing every year. The precise measurements, which began in the early 1990s, show that this rise has been accelerating since that date, mainly as a result of ice melting in Greenland and Antarctica. That is, not only sea level increases, but also increases faster and faster.

But what was not known was whether this acceleration had been occurring since before the measurements, nor where and why it would have originated in that case. Now, an international study has added new calculations to investigate the past, thanks to data provided by stations in  areas near the coastline. The results conclude that the acceleration of the sea level rise has been occurring since the 1960s and that they have influenced other factors besides the melting of ice.

The change in the oceans has been taking place for half a century. The new study, published by Nature Climate Change, indicates that the global sea level rise has increased from less than one millimeter per year in the 1960s to more than three millimeters per year today. 

Greenhouse gas emissions have been warming the planet around 1º from pre-industrial times until reaching the climate emergency we are in today. And that rise in temperature also causes the sea level to grow across the globe for two reasons. “There is an obvious one, the ice that melts and adds more water to the oceans; but another more complicated is the absorption of heat, which causes a thermal expansion of the water increasing its volume”, explains Francisco Mir Calafat, a researcher at the National Oceanography Centre of the United Kingdom and co-author of the study, together with Marta Marcos, from the Mediterranean Institute for Advanced Studies.

But, despite what one might think, this rise in sea level does not occur uniformly across the planet. There are other factors that influence that water and heat are redistributed by the Oceans unevenly, such as the course of the winds, the circulation of the waters and even the changes in the Earth's gravity field. In this case, according to the reports, the acceleration began to take shape in the South Pacific and the winds played a decisive role.

The new calculation not only serves to determine the acceleration in the past times, but also to alert what may happen in the future. The findings of this study highlight the important role that thermal expansion plays in the rate of sea level rise causing this acceleration, which had already been predicted by the 2013 Intergovernmental Panel on Climate Change for the 21st century. Thus, If we project the current conditions into the future, assuming that it will continue constant, the sea level increase could be more than double that expected for the year 2100, compared to projections that assume a normal increase rate. 


Heavy sea, Viña del Mar, Chile.
"Pacific" Ocean, Chile
Photo: revistaenfoque.cl
"The acceleration that occurs after the 90s is attributed to the melting of Antarctica and Greenland, but we see that it began in the 60s due to heat absorption," says Mir. He added: "The changes of the wind cause in turn changes in the circulation of the Ocean, which has led to this greater absorption of heat that causes the sea level to rise." In the subtropical South Pacific, East of Australia and New Zealand, the acceleration of the rise has been five times faster than the global average. For Mir, it is most likely that this alteration in the circulation of the roaring winds of the South has to do with climate change, but it is not something they have studied in this work.

"The new evaluation of the tide gauges shows an acceleration similar to that recorded by satellites from space in the last 25 years," says the geophysicist Carling Hay of Boston College, which means that the analysis of the study is robust. Researchers have developed a hybrid model that takes advantage of the global data of satellites and those offered by tide gauges, whose measurements are based on coastal points.

Translated by: Raul Silva M.
Sourcechiledesarrollosustentable.cl


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