Where I live in Southern California, it’s not uncommon to see 10-foot waves crash on the beach and then roll back out. Like tides and storm surges, waves come and go. Standing on the beach watching the waves roll in, it can be hard to get excited about global sea level rise, which until now has been measured in inches. But sea level rise is here to stay. A red line marches upward across my computer screen, charting nearly 20 years of global sea level rise as measured by satellites. The waves may be more dramatic, but the satellites give us context for the present and point a finger toward the future.
Last week, U.S. residents were reminded that rising sea levels are not just a distant problem faced by remote Pacific Islands. In work published March 13, Ben Strauss and colleagues of Climate Central reported that by 2030 nearly 5 million U.S. residents could be at risk from flooding as storm surges and high tides are reinforced by the ongoing rise of the seas. States like Florida, Louisiana, California, New York and New Jersey are especially vulnerable because of their densely populated coastlines.
Scientists still struggle to predict global sea level rise in the decades to come. Our best guess for the 21st Century lies somewhere between 1 foot (30 cm) and 7 feet (2 meters). However, no one is predicting global sea level will fall during the next 100 years. Covering more than two-thirds of our planet’s surface, the oceans expand as they absorb heat trapped by human-emitted greenhouse gases and collect melt-water from glaciers and ice sheets—processes that are almost impossible to reverse. We won’t see ice sheets grow or see the oceans cool for many generations. In fact, sea level is expected to rise for hundreds, perhaps thousands, of years even if carbon dioxide levels could be stabilized immediately. This makes sea level rise a profound indicator of human-kind’s irreversible footprint on Earth’s climate.
But let’s go back to the beach. Each individual coastline contends with a unique blend of local issues, and not every ebb and flow can be blamed on global warming. The land itself rises along some coastlines, and falls along others. What’s more, there are natural changes in the ocean like the Pacific Decadal Oscillation, which involves a decades-long reorganization of warm water across the Pacific. In California for example, this natural cycle has masked out 2 inches (5 cm) of global sea level rise since the early 1990s.
So how do we know whether changes are here to stay or are just part of a natural cycle? One of the most important tools we currently have for measuring sea level rise is the Jason-2 satellite and its predecessors. 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. If water is the lifeblood of our planet, then these satellites measure its pulse. But they also measure its fever. The 2 inch rise in global sea level since the early 1990s is one of the most poignant indicators we have of human interference in the climate. Two inches may sound small, but it equals more than 4000 cubic miles of extra ocean. For generations to come changes of this magnitude are irreversible.
But these satellites do more than hearken back to a bygone climate. If sea level rise accelerates as expected, satellites like Jason-2 will be the first to detect it. Given the uncertainty in predicting future rise, charting the changes in present day rates is even more essential. In effect, the Jason satellites function as our early warning system for sea level rise.
Despite its importance, we struggle to maintain the satellite record of global sea level rise. Designed to last five years Jason-2 is nearly four, and its successor Jason-3 has suffered delays. Although much of the satellite has already been built, budgetary constraints have delayed selection of the rocket and the launch date has slipped to the spring of 2014 at the earliest. Setting budget priorities in difficult economic times is always a challenge, but it would be a shame to break the satellite record of global sea level rise. As society faces a new human-made climate, records like these will guide us into the future. The oceans have an important story to tell us, assuming we are willing to listen.
Josh Willis, PhD, is a climate scientist at NASA’s Jet Propulsion Laboratory where he studies global warming and sea level rise using data from NASA’s many Earth observing satellites. He also likes the beach.
The views expressed in ecoView are those of the author and are not necessarily those of Ecology Global Network. EGN does not verify the accuracy or science of these articles.