Almost three-quarters of Earth’s surface is covered by oceans, and another 10% is covered by ice sheets and glaciers. The ocean holds 60 times more carbon than the atmosphere and absorbs almost 30% of carbon dioxide (CO2) emissions from human activities causing the ocean to warm. The warming of Earth is primarily due to accumulation of heat-trapping greenhouse gases, and more than 90% of this trapped heat is absorbed by the oceans. 2021 set a new record for ocean heating. As the water warms, it expands: about half of the sea level rise over the past twenty five years is attributable to warmer oceans.
Caused by four main factors, of which two are global (ice melting and warming waters that expand) and two are local (a slowing Gulf Stream and sinking land), the amount and speed of sea level rise varies by location.
NASA says that seas have risen by 6-8 inches in the last 100 years (nearly 4 of those since 1970), with some locations rising more than 9 inches. They anticipate an unavoidable rise of several feet in the future. At a current rate of about one inch every eight years, the consequences are staggering:
- creating more dangerous and powerful hurricanes and storm surges. Storm surge happens when waters rise above their normal levels and are pushed inland by wind. With Hurricane Katrina, it was the storm surge that caused the levees to fail, leading to destruction in the New Orleans area; it was Helene’s storm surge that killed twelve near Tampa; and Milton’s in October 2024 where storm surge created hundreds of millions of dollars in damage.
- more intense and frequent flooding. In the last 25 years or so, the number of days with high-tide flooding has increased by a whopping 250% or more in many regions, including along the Gulf of Mexico, and in the Mid-Atlantic and the Pacific Islands. On average, the U.S. now experiences five extra days of high-tide flooding each year compared to the year 2000.
- In the United States, almost 40 percent of the population live in relatively high-population-density coastal areas, where sea level not only plays a role in flooding, but also in shoreline erosion, and hazards from storms. You might be surprised to learn of the creation of ghost forests.
You might also want to watch a 4-part PBS series Sinking Cities which takes a look into how four cities (Miami, London, Tokyo, & New York) — all at particular risk — are adapting.
Flood Factor is a fascinating site where you can explore your flood risk. Scroll down on their Main Page where you can enter an address and learn about its risk from floods, fire, wind, Air or Heat.
Accelerating 
