Gauging the uncertainty of sea level rise

Climate scientists know a lot about climate changes with a high degree of certainty.

Scientific agreement on the broad strokes of climate change is high. We have good metrics telling us the planet is getting warmer. We know the severity of extreme weather events is on the rise. There is more than enough certainty on the big picture of climate change to be "actionable."

But there is still a significant degree of uncertainty on the finer resolution of how some specific climate change effects will unfold. How will specific regional effects manifest as the bigger global climate system changes? What's the precise time scale of climate changes? It's important to communicate the areas of continued discovery and investigation as climate science unfolds.

One area with a high degree of uncertainty is sea level rise.

Just how quickly will sea levels rise in the coming decades? How unstable and sensitive to warming are the massive ice sheets over Greenland and Antarctica? How quickly will sea levels rise as massive amounts of fresh water is injected into our oceans? Is the rate of sea level rise a straight line, or could it be potentially rapid and catastrophic as large sections of ice sheets collapse?

There's a lot of debate going on right now in the climate science community about how quickly sea levels will respond to climate warming.

John Upton from Climate Central has an eye opening piece on why residents of Tybee Island, Ga., are worried after unprecedented flooding from King Tides last fall.

I pulled some key excerpts from John's piece below. It's a worthy read.

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Councilmembers of an island town in Georgia met in a police station near sandy beaches last week to mull a plan for coping with worsening floods. The meeting followed unprecedented king tide floods in the fall that inundated the island and nearby Savannah, and shut down the highway that connects them.

“We’ve had more frequent flooding in areas that haven’t flooded before,” said Jason Buelterman, mayor of the beach town on the eastern shore of Tybee Island, where the population of a few thousand residents swells each summer with vacationers. “In November, water was coming into people’s garages and stuff. It had never happened before.”

Mayors from small towns, planners from the world’s largest cities and U.N. diplomats are being guided on the details of a looming coastal crisis by sea level projections compiled by a U.N. science panel. The panel’s work includes warnings about the amount of flooding that could be caused by melting in Antarctica, and those warnings have been growing bleaker.

The barren continent — the planet’s greatest reservoir of ice — remains shrouded in frigid mystery, and a lack of scientific knowledge about its ice sheet means scientists can’t yet predict how much flooding it could cause as temperatures continue to climb. A recent study, though, added to concerns that it could begin disintegrating, inundating coastal neighborhoods around the world, unless the heady goals of the new U.N. climate pact are achieved.

The Intergovernmental Panel on Climate Change’s most recent findings, from three years ago, appear to have underestimated the potential seriousness of the Antarctic problem, with sweeping implications for the urgency of pollution cuts — and for the futures of coastal communities like Tybee Island’s.

Instead of the anticipated several feet of sea level rise this century if current pollution rates continue, the latest modeling-based science warns that melting could lead to twice that amount. That sobering estimate is a rough one.

If the Paris agreement fails to substantially curb global warming, the latest projections suggest places like Tybee Island, which has an average elevation of less than 8 feet, could effectively be doomed.

The main question is no longer whether the ice sheets in Antarctica and Greenland will melt. It’s how quickly the changes will occur. That’s a difficult question to answer based on limited observations that are available from one of the remotest, coldest and least accessible parts of the world.

“As we learn more, we’re finding that the changes could be greater and more rapid than we previously thought,” said Penn State atmospheric science professor Michael Mann.

Clues for the future of a warming world are being culled from research into prehistoric coastlines that now sit dozens of feet above current sea level. They date back to periods when natural fluctuations pushed temperatures to levels that appear analogous with those of today.

“We know, with reasonable confidence now, that we have destabilized enough ice, such as through the melting of the west Antarctic ice shelves, to eventually give 10 to 14 feet of sea level rise,” Mann said. “What’s less certain is how quickly that could happen.”

More than five inches of sea level rise in the 20th century led to regular high-tide floods across the East and Gulf coasts, where erosion and subsiding land worsen the problem. It also amplified the crippling effects of Hurricane Sandy’s storm surge.

The seas are rising faster now, which could affect more than 100 million Americans and billions of coastal residents of other countries during the decades to come, requiring heavy spending on the replacement, protection and retrofitting of coastal roads, pipelines and neighborhoods.

Climate science is advancing with extraordinary speed as global teams of physicists, ecologists, oceanographers and geologists collaborate to address unanswered questions. Diplomatic procedures and science journals are struggling to keep up.

Ice sheet models still “have a long way to go before they’re fully credible, but they’re improving” said Princeton professorMichael Oppenheimer. “Modeling has progressed a lot in the last 10 or 15 years, and you’re seeing in the DeConto and Pollard paper the fruits of some of that progress.”