Surging seas put U.S. cities at risk

We often think of climate change as a slow motion, future process. But the reality of climate change is increasingly here and now.

Climate changes manifest in many ways, creeping into our daily weather patterns and even into your local and national news as climate-juiced supercharged extreme weather events like the recent South Carolina mega-flood.

For many, climate change doesn't hit home, until it does. By then it's often too late for effective response.

Sea level rise is one effect of a warming climate. The stealthy background hum of rising seas from glacial meltwater and thermal expansion as oceans absorb additional heat is a slow process. But when the increasingly higher "base state" of our oceans is driven inland by storm surge, or seasonal king tides in cities like Miami, higher sea levels suddenly become an expensive problem. We live in a world of mutualized risk. We all pay more through increased climate-driven insurance losses and big national infrastructure projects. The city of Miami Beach is already spending $300-million on a series of 60 pumps to try and hold back the rising tides.

Low lying coastal areas like Miami Beach are already under liquid assault from increasing flooding from rising seasonal tides. This fall the king tides in Miami are among the highest observed. Water levels now during king tides are rivaling some of the highest surges from previous hurricanes like Sandy and Irene.

The Washington Post's Capital Weather Gang elaborates on how seasonal 'nuisance flooding' from king tides is becoming more chronic as sea levels rise.

Here are some selected clips.

King tides. Nuisance flooding. Coastal flood advisory. Road closed. These are phrases that are commonly heard and seen this time of year in the Miami area, especially in low-lying Miami Beach. The highest astronomical tides of the year are coming up in the next couple of weeks, and if these past few are any indication of what’s to come, the Miami area could see some of the highest flood levels that have been observed in decades — even on a perfectly sunny day.

The official water level gauge for the Miami area is located on Virginia Key, a small island east of downtown Miami and south of Miami Beach. Specifically, the gauge is on the end of a dock on the University of Miami’s Rosenstiel School campus. It’s been the official gauge since 1996.

Actual readings from the Virginia Key gauge have been running anywhere from 6 to 12 inches above the predicted tides since mid-September. This has caused tidal flooding problems day after day in the sensitive, low-lying areas of Miami Beach.

There are a few factors coming together to create this extended period of tidal flooding. First, the tides are naturally highest in September and October here due to predictable seasonal oceanic factors.  Specifically, the ocean is warmest at the end of summer, and water expands as it warms.  Secondly, the velocity in the Florida Current portion of the Gulf Stream is weakest during October, so water literally piles up along the Florida east coast leading up to that minimum.  On average, high tides are about 10 inches higher in October than they are during February. We can count on that every year.

And then there’s sea level rise, which is not solely responsible for exceptionally high tides, but it does gradually raise the background water levels. Just over the past 20 years, sea level has risen by nearly 4 inches in the Miami area, and by roughly a foot in the past 100 years. Year by year, in a slow-motion crisis, the baseline creeps up — and what’s troubling is that therate of the increase has been accelerating.

Each inch of sea level rise makes it easier for high tides to flood areas that never used to flood, and for storm surges to reach places they previously wouldn’t have. Sea level rise makes “nuisance flooding” an increasingly common occurrence, to the point where it becomes chronic flooding.

King Tides explained

As climate change raises sea levels, the elevated base state of sea level makes 'routine' coastal flooding worse. How do king tides work? Here's a good explainer form NOAA on the process of coastal tidal flooding.

Surging Seas

The longer term picture over decades for many U.S. coastal cities is increasingly dire. Solutions are expensive, and in many cases we can only hold back the rising ocean for so long until the next catastrophic hurricane event overwhelms coastal infrastructure.

Climate Central has put together an eye opening look at just how vulnerable 414 U.S. cities are to rising seas as our climate changes. It's called Surging Seas, and it looks at the most likely scenarios for U.S. coastal cities in an era of rising sea levels.

Most of the population in 414 U.S. municipalities lives within 5 feet of the current high tide line. Carbon pollution we have already emitted will heat the planet for hundreds of years. This committed warming locks in about 5 feet of sea level rise.

Historic carbon emissions have already locked in enough future sea level rise to submerge most of the homes in each of several hundred American towns and cities, according to Climate Central-led research published Monday inProceedings of the National Academy of Sciences. The animated timeline on this page maps, year by year, how the total number of locked-in cities could climb to more than 1,500, if pollution continues unchecked through the end of the century. It also lays out an alternative timeline based on extreme carbon cuts, leading to fewer than 700 locked-in cities. You can watch threats unfold nationwide or for individual states, and track the potential fate of each municipality. 

Our research does not project, and this animation does not show, exactly when sea level will reach heights great enough to pose these dangers — likely centuries. Rather, our findings assess when enough carbon pollution will have accumulated, under each scenario, to lock in future sea level rise posing existential threats for each town or city — sea level rise that could submerge land where more than half of today’s population lives. This summary discusses the research and findings further.