Manmade Global Warming - New Extremes, page-9075

GLOBAL SEA LEVEL CHANGE

Global mean sea level rose rapidly following the last ice age approximately 20,000 years ago. However, the rate of sea level rise slowed and has been nearly stable over the last few thousand years. Since around 1900, global average sea level has risen by about 7-8 inches (Hayhoe et al. 2018, NCA4) and the rate of sea level rise has been accelerating in recent decades as ocean temperatures warm. Nearly half of this rise in sea levels has occurred since 1993, and the rate of global mean level rise since 1993 has been approximately 3.4 mm per year. It is virtually certain that global mean sea levels will continue to rise throughout the 21st century and beyond.

The main contributors to changes in global mean sea level are thermal expansion caused by warming ocean temperatures, melting of land-based ice that results in the addition of fresh water into the ocean, and local land water storage (e.g., water that is pumped from land or impounded by dams or other structures). Sea level rise can vary across the coast due to ocean currents and tidal fluctuations.

Data on sea level changes come from multiple sources, primarily from tide gauges, coastal buoys, and satellite altimeters. Models are also used to estimate changes in sea levels, particularly where no data are available.

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orida and the Rising Sea

By Ben Strauss

Note: First published in the Miami Herald

Florida is in the crosshairs of climate change. Rising seas, a population crowded along the coast, porous bedrock, and the relatively common occurrence of tropical storms put more real estate and people at risk from storm surges aggravated by sea level rise in Florida, than any other state by far.

Some 2.4 million people and 1.3 million homes, nearly half the risk nationwide, sit within 4 feet of the local high tide line. Sea level rise is more than doubling the risk of a storm surge at this level in South Florida by 2030. For the hundreds of thousands of Floridians holding 30-year mortgages, that date is not far off in the future.

The world’s oceans are already rising, thanks to global warming. Global average sea level has gone up about 8 inches since 1880. In South Florida, taxpayers are already paying the price for climate change as salt water pushes through porous bedrock into coastal drinking-water supplies, and rivers and canals choked by heavy rains have a harder time draining into the ocean. A recent Florida Atlantic University study estimated that just 6 more inches of sea level rise — very plausible within two decades — would cripple about half of South Florida’s flood control capacity.

It’s now, not later, for sea level rise in South Florida.

That’s a big reason why Climate Central has worked for two years on a new analysis of this threat, blending storm surge, tides and more into the picture. Integrating storms and tides show that a small amount of sea level rise can make a big difference — multiplying the odds of extreme coastal floods around the United States, not just South Florida. Think of it like raising the floor at a Miami Heat game: you’d see a lot more dunks. Overall, sea level rise is making the odds of a South Florida flood reaching more than 4 feet above high tide, by 2050, on par with the odds of losing at Russian roulette.

More than half the population of more than 100 Florida towns and cities lives on land below that 4-foot line. Miami-Dade and Broward counties each have more people below 4 feet than any state, except Florida itself and Louisiana.

Just how vulnerable any area is depends on many elements. Our analysis factored in not only local sea level rise projections, storm-surge patterns and tides, but also local topography and patterns of development. In an attempt to better inform people, businesses and planners who live and work near the coast, we have mapped and evaluated risk in 3,000 towns, cities and counties across the lower 48 states, including South Florida, and have created a free, ZIP code-searchable map with neighborhood views and risk information at SurgingSeas.org. Among our key national findings:

Global warming has already doubled or tripled the odds of extreme high water events over widespread areas of the U.S. coast.

Widespread areas are likely to see storm surges on top of sea level rise reaching at least 4 feet above high tide by 2030, and 5 feet by 2050.

Nearly 5 million U.S. residents currently live on land less than 4 feet above high tide, and more than 6 million on land less than 5 feet above.
https://sealevel.climatecentral.org/news/floria-and-the-rising-sea