Causes of Sea Level Rise

Sea level is rising — and at an accelerating rate — especially along the US East Coast and Gulf of Mexico

• Global average sea level rose roughly eight inches from 1880 - 2009.
• The average annual rate of global sea level rise accelerated from 1993 - 2008, increasing 65 - 90 percent above the twentieth century average.
• The US East Coast and Gulf of Mexico experienced some of the world's fastest rates of sea level rise in the twentieth century due to local and regional factors.

Global warming is the primary cause of current sea level rise. Human activities, such as burning coal and oil and cutting down tropical forests, have increased atmospheric concentrations of heat-trapping gases and caused the planet to warm by 1.4 degrees Fahrenheit since 1880.

• Rising temperatures are warming ocean waters, which expand as the temperature increases. This thermal expansion was the main driver of global sea level rise for 75 - 100 years after the start of the Industrial Revolution, though its relative contribution has declined as the shrinking of land ice has accelerated.
• Land ice—glaciers, ice caps, and ice sheets—is shrinking at a faster rate in response to rising temperatures, adding water to the world's oceans.
• As the rate of ice loss has accelerated, its contribution to global sea level rise has increased from a little more than half of the total increase from 1993 - 2008 to 75 - 80 percent of the total increase between 2003 - 2007.

Roughly a third of the US population—more than 100 million people—live in coastal counties. Coastal states with large areas of low-lying land, including Louisiana, Florida, North Carolina, California, and South Carolina, are particularly vulnerable to rising seas and coastal storm surges. The risks to coastal states include:

• Shoreline erosion and degradation. Rising sea levels allow waves to penetrate further inland, even during calm conditions, increasing the potential for erosion.
• Amplified storm surges. Coastal storms often cause storm surges, which occur when high winds push water inland. With rising seas, storm surges occur on top of an elevated water level and reach farther inland, with potentially catastrophic damage to homes and infrastructure.
• Permanent inundation. Many low-lying coastal land areas are expected to be gradually submerged by rising sea levels. A rise of two feet above today's sea level would put more than $1 trillion of property and structures in the US at risk of inundation, with roughly half of that value concentrated in in Florida.
• Saltwater intrusion. Saltwater can reach further into coastal groundwater sources as sea level rises, increasing the salinity of freshwater used for drinking and agriculture.

Communities must weigh the costs and risks of accommodating the rising seas, retreating from them, or trying to defend coastal properties and infrastructure with protective measures