A sea level rise of five-to-ten centimetres by the year 2050, which is what most models currently predict for our future, could double the frequency of major coastal flooding in lots of places around the world, according to a new study in Scientific Reports. For cities like Vancouver, London and New York, and for the Tropics, this could spell disaster.
Sea level rise is mainly due to the melting of land based ice in Greenland and Antarctica. Greenland locks away enough ice to account for about seven-to-eight meters of sea level rise, and if Antarctica completely melted, it would add 70 meters of sea rise, lead author Sean Vitousek of the University of Illinois told Motherboard over the phone.
This is an unlikely outcome, but nonetheless, "even if a small percentage of these ice masses melt, you can get into sea level scenarios that are pretty large," he said. By the end of the 21st century, seas are forecasted to rise by about one meter.
Vitousek found it would not take much to double the amount of rare but devastating coastal flooding that seaside cities face. Ocean levels would just need to rise another 5 cm to inundate tropical areas including communities on the Indian Ocean, Hawaii, and the city of Miami twice as often as they do now. And an extra 10 cm would be all it takes for areas like Seattle and Vancouver to see the usual 100-year flood levels every 25 years.
Many cities are preparing for the growing threat of sea level rise and other effects of climate change. New York, for example, has focused on building flood barriers, and Vancouver has considered the possibility of moving some infrastructure away from the coast if it gets bad enough. Canada also included a $2 billion climate disaster mitigation fund in its most recent budget. But critics say that some places aren't keeping up, or doing enough.
In this new study, Vitousek said, they tried to approach the problem differently. The researchers were interested in learning about small amounts of sea level rise associated with a set amount of flooding frequency. "We specified that we were interested in the doubling of the frequency and then we tried to find the sea level rise associated with that," he explained.
By using a statistical analysis model, Vitousek was able to gauge the impact of sea level rise that will contribute to more flooding in the different parts of the world, taking into account the variables of tides, storm surges, and waves. Previous studies have not considered how high waves can add to flooding.
"[Before], we had our eyes on the ocean and our backs to the land, so we didn't account for the topography that would potentially mitigate these floods," he said. On top of that, because of the inclusion of waves in the analysis, they found that flooding could be more destructive as unpredictable and high waves could overcome current protective infrastructure.
Vitousek used a method called extreme value theory, a branch of statistics meant to account for extraordinary, but random, events. The idea is to isolate those random events to measure their big picture impact.
"The statistical behavior of tides, waves, and storm surge varies pretty significantly around the globe," said Vitousek. Yet, in this study, he found that the growing sea-level was pretty much uniform across the planet.
"So how do you get certain areas that are more or less vulnerable than others? We can use these statistical models to answer this question."
Vitousek agrees that removing buildings and moving away from the shoreline, like what Vancouver has considered, is a possible solution, but it might not work everywhere. "How are we going to move New York City?" said Vitousek. As for Miami, "there are very few areas where you get about three meters above sea level. So, moving those whole cities just doesn't seem to be the most realistic option."
He thinks that reducing greenhouse gas emissions is the best way to slow the rising sea.
"We should really start thinking about how to reduce emissions and even going so far as [figuring out] how do we remove CO2 from the atmosphere actively," said Vitousek.
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