One tenth of an inch per year. That is the number that could lead to eventual flooding of some of the world's largest coastal cities. The slow but steady sea level rise off the coasts of Galveston, New York, Baltimore, San Francisco and many other cities hint at the warming world we'll inhabit by the end of the century. Although uncertainties remain about the exact magnitude and speed of future changes, satellites and tide gauges both agree that sea levels have risen worldwide by about 5 to 9 inches during the last century.
Since no one has been standing around measuring each tide since 200 BCE, scientists used fossils of microscopic algae called foraminifera of coastal salt marshes in North Carolina to track rising sea levels. Their carbon-dated results show ocean levels remained remained relatively stable during the last 2,000 years, rising only about 1/50 inch annually during a 400-year period. But in the late 1800s--right around the industrial revolution--that rate took off. Today, seas are rising about one-tenth of an inch each year, and it has been accelerating even since the 1960s.
Fractions of an inch might not sound like much, but the Organization for Economic Co-operation and Development figures at least 150 million people and trillions of dollars in property will be standing in the way of severe coastal flooding by 2100, mostly in the developing countries of Asia (although Miami made the top 10 list). While cities will not be fully inundated, they will be much more vulnerable to coastal floods and storms, and demand pricey counter measures such as the $1.2 billion the Dutch plan to spend annually on flood control.
If climate models are right--and the study reinforces the results of existing temperature and sea-level simulations--then the oceans could surge more than three feet by the end of the century, making once-a-century storms into a nearly annual occurrence. New York, along with much of the Atlantic seaboard, could experience routine flooding, including large parts of Queens and Brooklyn. The effects are already being felt in places like low-lying Bangladesh, and the low-lying Pacific islands where climate refugees are moving to higher ground.
[Image: USGS's Flickr stream]