An extreme climate event between 2014 and 2016 caused a sharp rise in global sea levels

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Between June 2014 and May 2016, the average sea level rose by up to 15 millimeters, or 0.6 inches.
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Between June 2014 and May 2016 average sea level rose by as much as 15 millimeters, or 0.6 inches. It may not seem like it, after all, this length is not much larger than the size of the nail, but in relation to long-term trends, it was a terrifying leap that surprised experts.

According to data from a NASA satellite, the global average sea level has risen by more than 9 centimeters, or about 3.5 inches, since 1993. From this, when they estimated the annual rate of ocean rise, scientists expected an average sea level would increase by about 8 millimeters between 2014 and 2016, but the recorded global sea level rise was almost double that predicted.

After years of speculation about this sudden rise in global oceans, a new study by a team from Laboratory of Physical and Space Oceanography of Brest Universityin France revealed the likely climatic events responsible for this unusual rise, and one of them is a well-known pattern: El Niño-Southern Oscillation (ENOS).

The impact of El Niño on the global oceans

According to research published on Geophysical Research Letters, apart from the obvious linear trend an average sea level rise of approximately 4 mm per year between 2006 and 2016, a large interannual variability is built into the series, and this variability is direct associated with El Niño and La Niña events.

Drought over the Amazon due to El Niño – the positive phase of the El Niño – Southern Oscillation (ENOS) – could be linked to global sea level rise, according to a new study.

The authors found in global data a 5mm drop in mean sea level during a La Niña event from March 2010 to May 2011, while an increase of 15 mm between June 2014 and May 2016 occurred concurrently with two subsequent El Niño events, one of which, 2015/2016, was the most intense on record.

The 2015/16 El Niño phenomenon, the strongest on record, was one of the main factors responsible for the sudden rise in mean sea level between 2014 and 2016. Image: Climate.gov/NOAA.

In the study, the authors explain that there are two main factors that are driving global sea levels: the thermal expansion associated with global warming of the oceans (known as the global mean thermosteric level) and the increase in global ocean mass (known as the barystatic level).

It increases in response to the melting of continental ice masses (Greenland and Antarctica), mountain glaciers and changes in terrestrial water supply. But how much did each of these factors influence the increase seen between 2014 and 2016?

The results of the research indicate that surprisingly in the period under review the barista contribution, i.e. ocean mass gain, had a very significant contribution of 12 mm to sea level rise, accounting for 80% of the total recorded. The remaining 20% ​​(3 mm) would be associated with thermal expansion due to warming oceans.

According to the study, drought in the Amazon basin caused by a lack of rainfall generated by El Niño was the main factor leading to sea level rise.

But what is behind this increase in global ocean mass? To answer this question, the researchers analyzed satellite data, ocean data, as well as land-based water storage data, such as data from large basins such as the Amazon basin. Thanks to this data, they found that a large part of the contribution (about 52%) came from South America, specifically from the Amazon River.

These unusual El Niño events have affected rainfall patterns around the world, reducing the accumulation of terrestrial water in the Amazon basin, which will lead to an increase in the global average mass of the ocean (Llovel et al., 2023).

During El Niño events, the tropical circulation cell over the Pacific is altered so that more precipitation falls on the central and eastern tropical Pacific Ocean and less on the Amazon—such as the current drought situation we are experiencing due to El Niño. This excess of precipitation over the Pacific and deficit over the Amazon Basin, which held less water than normal, led to an increase in global ocean mass, aided by the melting of polar ice during the same period..



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