Study warns sea level could rise 20 meters but local experts are more cautious

Dangerous sea-level rise

A study warns sea level could rise 20 meters but local experts are more cautious

Sunday, December 29, 2019 – 7:15 AM

By Gerardo E. Alvarado León

According to the National Oceanic and Atmospheric Administration (NOAA) in San Juan, where systems have been collecting data since 1962, the average sea level rise was .199 millimeters. (GFR Media)

While at the recent U.N. Climate Summit (COP25) negotiations between nations focused on keeping the average sea level rise to 2 meters, new research suggests that the planet is already facing a 20-meter rise over several centuries.

Such a scenario would be devastating for Puerto Rico, said Aurelio Mercado, a retired physical oceanographer. According to his analysis, much of the coast in the northern half of the island, between Arecibo and Río Grande, would be underwater, as would happen to part of the coast in the southern half, between Ponce and Patillas.

However, the southwestern area -between El Combate (Cabo Rojo) and Guánica- would suffer the most dramatic effect, since the sea would separate that part. In Mercado’s words, that area of Puerto Rico “would become a separate island.

“Even if they comply with all the agreements being discussed at the IPCC (United Nations Intergovernmental Panel on Climate Change and the World Meteorological Organization), we are already exposed to a rise in sea level for years and centuries,” he told El Nuevo Día.

“A 20-meter rise seems likely to happen by the year 2200, or more and, although it seems like a very distant date, it is not really so and the consequences for Puerto Rico are really serious,” he added.

Mercado based his analysis on research by James White, a professor in the Department of Geological Sciences at the University of Colorado at Boulder, published in Discover magazine earlier this month. He used the Climate Central’s Surging Seas mapping tool to estimate the impact of a 20-meter sea level rise in Puerto Rico.

“This is unstoppable. We have to start thinking about moving away from the coast (relocation), which is something that developers don’t like. Once you have permanent flooding, who’s going to want to live in those areas? Coastal construction is going to be impacted by the sea,” Mercado warned.

Historic Numbers

On the other hand, Mercado pointed out that last November, tide gauges in San Juan Bay and Magueyes Island in La Parguera reported a record rise in sea levels.

According to the National Oceanic and Atmospheric Administration (NOAA) in San Juan, where systems have been collecting data since 1962, the average sea level rise was .199 millimeters. Meanwhile, in Magueyes, where they have been collecting data since 1955, it was .181 millimeters.

“The tide gauge in Magueyes clearly shows what is happening at Las Salinas de Cabo Rojo,” Mercado said, referring to the intrusion of seawater into the area where salt has been extracted for 508 uninterrupted years for commercial purposes. On December 11, the Department of Public Safety confirmed an emergency situation in Las Salinas and they are now waiting for short-term mitigation projects.

In Magueyes, the highest sea-level rise is generally in September. Mercado warned, however, that this year rising sea levels continue even in September and October. “It was in November that they recorded the highest sea-level rise. What will happen in December? By October and November, the sea level started to drop because waters were getting colder, but this year that didn’t happen,” he explained.

According to Mercado, the activity of the San Juan tide gauge “has also been anomalous.” The highest sea-level rise in history was recorded last November. “By the way, the sea level rise rate recorded last November is the third highest in history, no matter what month it is,” he said.

The physical oceanographer said that, at both stations, the rise in sea level “is accelerating again”, after a brief pause between 2015 and 2017.

“Plausible scenarios”

For Ernesto Díaz, coordinator of the Puerto Rico Climate Change Council, Professor White’s research published by Discover provides “guidance and scenario planning” regarding sea level rise.

He stressed, however, that the study does not specify when the 20-meter rise would happen, so he opted for more conservative projections. El Nuevo Día contacted White by email for an interview but received no answer by press time.

“The important thing about projections is that they are scientifically sound and that they indicate the projected rate, the scenarios and methods used, and especially they should state the date when each level would be reached,” said Díaz, who is also the director of the Coastal Zone Management Program of the Department of Natural and Environmental Resources (DNER).

Díaz cited research by oceanographer and climatologist Stefan Rahmstorf, who found that “at the height of the last Ice Age, 20,000 years ago, global sea level was a full 120 meters lower than today.” Rahmstorf’s findings were published in Nature and Science.

He also referred to the studies by climatologist William Sweet and climate scientist and geobiologist Robert E. Kopp, whose projections of sea-level rise by 2100 place “plausible scenarios” between 2 and 2.7 meters.

“Based on the projections of the global models adjusted to our reality in Puerto Rico, using data from the tide gauges in San Juan and Magueyes, and altimetry data available at NOAA, Dr. Sweet and this servant, among others, estimate an intermediate scenario of approximately one meter and an extreme scenario of approximately three meters at 2100,” Díaz said.

He also explained that as part of the island’s reconstruction process after Hurricane María, the new coastal infrastructure “has to adapt” to the new rising sea level scenarios.

Coastal Erosion

Geologist and oceanographer Maritza Barreto was also cautious about Professor White’s research, pointing out that when the 20-meter rise would happen is not clear.

“It’s important to know that detail in order to evaluate whether the results of the model are exaggerated or not. The projection presented could happen based on the island’s topography, but when? That is the important part,” said Barreto, current Director of the Coastal Research and Planning at the University of Puerto Rico, Río Piedras.

Barreto considers Mercado´s study is clearer since it evaluates “the sea level rise in Puerto Rico until November 2019 using data from the tide gauges in San Juan and Lajas, where he finds that there is an acceleration and that it has been consistent since 2010,” the expert added.

Barreto, who is also the president of the Caribbean and Puerto Rico Beach Network, said that coastal erosion is perhaps the most visible effect of sea-level rise on the island.

In her research, she found that, since 2012, erosion has evolved from high to severe in several areas of the island, such as Punta Uvero in Loíza, different parts of the Arecibo coast and Punta Guilarte in Arroyo. In her opinion, these areas could “support this new scenario” that anticipates that in case of swells and waves associated with cyclones, floods would reach further inland and, therefore, there would be more erosion in certain areas.

“The option that sea-level rise could cause sediment deposition on some beaches cannot be eliminated. This is an ongoing analysis,” she said.

Waiting to be called

Climatologist Rafael Méndez Tejeda, director of the Atmospherical Research Lab of the University of Puerto Rico at Carolina, said that debates such as the one proposed by Professor White should be discussed in the Committee of Experts and Advisors on Climate Change, created by Law 33-2019.

Méndez Tejeda and Barreto are members of the Committee, as well as environmental scientist Pablo Méndez Lázaro, engineer Carl Soderberg, meteorologist Ada Monzón and global renewable energy specialist Roy Torbert.

“The problem is that we’re ready to work, but we’re not being called. It’s up to the Natural Resources secretary to call us in,” said Méndez Tejeda, in referring to Armando Otero Pagán, who is the DNER acting director after Tania Vázquez resigned.

Law 33-2019 establishes, among other things, that the Committee will be given until May 22, 2020, to have the mitigation, adaptation, and resilience plan for Puerto Rico ready. This plan will be evaluated and approved by the Legislative Assembly.

Méndez Tejeda insisted, however, that if they are not called to work, the plan will not be ready on the date set.

“The Natural Resources secretary is the one who chairs the Committee and, therefore, he is the one who has to call us. We have no power in law to call ourselves in. We were supposed to have started in the summer, but our appointments were confirmed later than expected,” the climatologist said.

Law 33-2019 was approved on May 22nd. Governor Wanda Vázquez appointed the members of the Committee on September 30. The Legislature confirmed them between October and November.

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