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Sunday, December 04, 2022

Bringing order to the chaos of sea level projections

In their effort to provide insights to decision-makers about the consequences of climate change, climate researchers from NIOZ, Deltares and UU are bringing order to sea level projections in large numbers, giving climate models an expected sea level rise. translating for. Their new observational study was published in the scientific journal Earth’s Future. “These results provide tools for decision making in the short and long term.”

Amy Slangen is a climate scientist at NIOZ and co-author of the IPCC Climate Report. Along with climate adaptation experts Marjolijn Haasnoot and Gundula Winters from Deltares and Utrecht University, also authors of the IPCC, Schlangen examined the similarities and differences between several sea level projections published in recent years.

eight families of estimations

“We found that the set of more than 80 different conjectures can be reduced to eight ‘families,'” Slangen says. “Within each family of projections that we have identified, researchers have often used similar data, but they have used different model approaches, for example. As a result, each new publication results in an estimated sea level rise.” , depending on whether the publication focuses on the short term or long term, or on the model used to estimate the processes due to the potentially large contribution of accelerated melting of the Antarctic ice sheet.”

These details are interesting to scientists, but make it more difficult for users to maintain observations. Slangen: “It can be an issue when you, as a government, have to decide what you are going to do to protect your coasts from rising sea levels. The decision-makers will adjust their policies with every new publication.” can not do.”

Half a meter increase before the end of the century

The researchers hope to dispel this doubt, as all families paint a similar picture for the first 50 cm of sea level rise. Slangen: “We’ll see the first half-metre rise before the end of this century, even if we start reducing greenhouse gas emissions on a large scale. For this period, it makes little difference whether you’re looking at sea level rise.” Which family do you use for estimations?

According to adaptation expert Hasnoot, this means we may already be starting to adapt to the consequences of sea level rise. “Those who have to make climate-proof decisions can already start. However, it’s important to take into account the uncertainty of the future. If you plan smartly, you make sure you’re half a meter under the sea right now. The level rise can be adjusted to a meter later. This will save a lot of money and effort.”

Model and emission scenario

The higher the sea level, the more diverse the eight families become. Slangen: “A meter sea level rise from 75 cm, it matters more which model approach you use and what climate scenario you follow. However such large values ​​can only be exceeded over the long term.” done, they may already be informed of adaptation decision making for the medium period. Each family is valued for a specific situation and at which point certain threshold values ​​are exceeded.”

Hasnoot: “In a sensitive area, for example, you can select a family with a large acceleration in the contribution of Antarctic melt. Many of the world’s major cities, such as London, New Orleans and Rotterdam, are in vulnerable areas. In such mega-deltas, relative sea level rise is even more rapid, for example due to groundwater extraction further downstream.

flowchart

In their publication, the authors present a flow chart that policymakers can use when deciding when and how to adjust, taking into account the extent of uncertainty in sea level projections. “For example, the timing of these sea level values ​​can be used to estimate how long a measure will remain in effect,” Haasnoot says. But also vice versa: given the desired lifespan, you can use these values ​​to design a protective measure.

Slangen: “For the first 25 centimeters of sea level rise, the time bandwidth is small: projections suggest this will happen before 2060. There will be a half-meter rise before the end of the century. The larger the sea level Growth, great uncertainty. Depending on the family, an increase of 1.5 to 2 meters may be reached by the year 2100, but it could also happen in 2200 or later.”

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