Sea levels are rising. What does that mean for coastal communities?

I am often get this question when I give my climate change presentation to community groups, service clubs or school classes: Should we in the United States continue to reduce our greenhouse gas emissions while countries like China keep increasing theirs?

China’s greenhouse gas emissions exceed those of the United States and other developed nations combined. In fact, more than a quarter of global greenhouse gas emissions comes from China.

With that said, China will face some of the most significant challenges of any other nation due to climate change and will have to dramatically reduce its emissions. Here is why.

China has an extraordinarily densely populated coastal region and is particularly vulnerable to rising sea levels.

According to a paper from Climate Central, an independent group of scientists and communicators who research and report the facts about our changing climate, if global temperatures rise 2 degrees Celsius (3.6 degrees Fahrenheit), 64 million people in China would be living in areas submerged by rising seas.

An increase of 4 degrees Celsius (7.2 degrees Fahrenheit) would cause that number to rise to 145 million people.

When water warms, it expands. This is because of the thermal expansion of the upper levels of the ocean.

That, along with melting glaciers and ice sheets in both hemispheres, pushes sea levels higher over time. Sea level variation is a vital indicator of climate change.

To make matters more concerning, as seas go up, the land goes down. The elevation of Central Shanghai, an economic juggernaut located on the southern estuary of the Yangtze River, has dropped 10 feet and now has an altitude of only 7 feet.

This condition will get worse as sea levels continue to rise and tropical cyclones become more intense.

However, another phenomenon in the 2030s may exasperate this already dire condition.

The tidal range is expected to increase — meaning that there will be lower ebb tides and higher flood tides.

According to research by NASA scientists, the regular wobble in the moon’s orbit occurs on an 18.6-year cycle.

Currently, the tides are being slightly diminished, but in the mid-2030s, during the latter half of this cycle, the situation will be reversed, which will create greater tidal ranges.

These circumstances are making the science of measuring and tracking sea levels more critical each year.

Satellites have been measuring the threat.

Years ago, NASA launched two satellites from what is now known as Vandenberg Space Force Base — launching Jason 1 in 2001 and Jason 2 in 2008.

In 2016, the National Oceanic and Atmospheric Administration and the European Organization for the Exploitation of Meteorological Satellites launched Jason 3 into space from Vandenberg with help from NASA.

These satellites measure sea levels over most of Earth using an extremely precise radar altimeter.

The altimeter transmits radio waves from the satellite to the ocean’s surface and measures the time it takes for the radio waves to bounce back.

This technique has proved to be particularly precise and accurate.

“These satellites give us a global view of our changing oceans with such exquisite accuracy that even the yearly rise and fall of global sea level is visible, caused by the transfer of water to and from the continents in the form of rain and river runoff,” said climate scientist Josh Willis of NASA’s Jet Propulsion Laboratory in Southern California.

Willis has been an authority on sea level changes for many years.

Sea level change is probably the best way to measure climate change.

“In the early 1990s when satellite measurements began, global sea levels were rising at about 2 millimeters per year,” Willis said. In the 2000s, it was closer to 3 millimeters per year, and in the most recent decade, sea levels have been rising by 4 millimeters per year, so the rate of rise is getting faster.

Most studies indicate the sea level will rise by as much as 4 feet by the end of the century. I know that may not sound like much, but such rises will have devastating consequences.

When combined with waves generated by high winds, storm surge, storm runoff and tides, the rising sea level could put millions of us who live along densely populated coastlines in harm’s way.

Given the uncertainty in estimating future sea-level rise, these satellites have become an early warning system.

Unfortunately, Janson 1 and 2 are no longer in service. They were designed to run for only five years, and Jason 3 has already seen 5 years of space service.

To replace the Jason satellites, the Sentinel-6/Jason-CS satellites were developed.

The Sentinel-6 Michael Freilich satellite, was launched in November from Vandenberg, and Sentinel-6 B is scheduled to launch in 2025.

Combined with the Sentinel-6/Jason-CS satellites will be the Surface Water and Ocean Topography (SWOT) mission, a future satellite altimeter jointly developed by NASA and the National Centre for Space Studies in France, in partnership with the Canadian Space Agency and United Kingdom Space Agency.

SWOT is targeted for launch no earlier than November 2022 from Vandenberg Space Force Base on a Space X Falcon 9 rocket.

The SWOT mission will give a much higher resolution over the water.

“It’ll be really exciting to see what the science community and the agencies like NOAA do with the ocean data,” Willis said. “But I think the big revolution from SWOT will be the surface water part. Hydrologists will get huge volumes of new data, so it’ll be a major revolution for them.”

How to reduce your carbon footprint

About 5 million tons of carbon dioxide (CO2) are dumped into the atmosphere every hour from the burning of fossil fuels.

To learn what you can do to reduce your carbon footprint, please visit PG&E’s website at pge.com.

Another excellent site is Dr. Ray Weymann’s webpage, Central Coast Climate Science Education, at centralcoastclimatescience.org or Climate Central at climatecentral.org.

This story was originally published August 3, 2021 at 5:05 AM.