Absent mankind’s carbon-spewing activities, the planet’s oceans would probably have risen half as much or even less over the last century, a team of climate scientists reported this week.
For South Floridians grappling with ever worsening seasonal tides, that should serve as a warning to scale back carbon emissions. The team, led by Rutgers University climate scientist Robert Kopp, found that seas rose faster during the last century than at any time during the previous 27. That has led to man-made flooding, including in parts of Florida, that have outpaced — in some cases many times over —what nature would have caused.
The authors also say that they confirmed what scientists have long suspected — that at the current rate, seas globally should rise three to four feet by the close of the century. That confirmation, however, comes with a big caveat: melting polar ice.
With little ice melt during the period they studied, the study — published Monday in the Proceedings of the National Academy of Sciences — was not able to account for the kind of polar meltdown now occurring. And that could be a problem, said University of Miami geologist Harold Wanless. Melting ice in Greenland has already caused sea levels to creep up, which scientists fear could accelerate rapidly if the planet continues warming. But the rate and amount are too variable to include in models.
“So what the modelers do is ignore them,” Wanless said. “They should have big uncertainty graphs.”
Still, scientiests consider the study important because it uses fine regional variations to forecast global changes, making it “bulletproof,” said Wanless’ colleague, atmospheric scientist Benjamin Kirtman, who co-authored the United Nations’ short-term projections for the International Panel on Climate Change.
“That’s important in this charged environment,” he said — meaning the political climate.
$346 billionThe amount of South Florida property at risk of flooding by 2100
And while other climate change studies have focused on temperature change, the study importantly highlights the dangers of sea rise and the increased risk of flooding. In Florida alone, up to $69 billion in property is expected to be at risk by 2030. That amount climbs to $346 billion by the end of the century, according to earlier analysis by the Risky Business Project.
No study has extended the links all the way from burning fossil fuels, to global warming, to sea level rise.
Environmental scientist Benjamin Strauss
“No study has extended the links all the way from burning fossil fuels, to global warming, to sea level rise, to coastal floods that were caused unambiguously by us,” environmental scientist Benjamin Strauss wrote for the research organization Climate Central in a separate report he co-authored with Kopp and others.
Since the beginning of the 20th century through 2014, sea levels rose globally by about six inches, the scientists reported. Using tidal gauges from 27 locations around the nation that date back to the 1950s, they found that without the additional half foot, about two-thirds of the nuisance flooding — the kind of inundation that now routinely floods streets in South Florida and makes it ground zero for sea rise — would not have occurred.
The authors say regional changes are important to incorporate in calculations because they can vary dramatically from global changes over vast periods of time, which can refute climate change deniers’ claims that the planet is undergoing a natural, periodic variation. For example, the authors found that while global sea levels rose up until the year 700, sea levels in New Jersey and North Carolina rose and fell at different rates because of changes in the Gulf Stream or inshore winds.
Think of it like it takes 10,000 studies to prove something right and one study to prove something wrong. This is one of those 10,000 studies.
University of Miami atmospheric scientist Benjamin Kirtman
“Think of it like it takes 10,000 studies to prove something right and one study to prove something wrong. This is one of those 10,000 studies,” Kirtman said. “The novelty is the preparation of the data, how you do quality control and make sure you’re looking at robust things.”
The study also dovetails with work Kirtman is doing to localize climate projections to provide more accurate forecasts for governments, planners, developers and anyone else looking for a future in low-lying South Florida. Up and down the east coast, the Gulf Stream will strongly influence sea levels. When the Gulf Stream is weak, sea levels will rise. When it strengthens, they fall, he said.
“Getting that Gulf Stream undulation, and how it’s affected by climate change, is really important for the regional aspect of sea level,” said Kirtman, who hopes to have a model to predict local changes over shorter periods of time finished in the next two years.