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An Early Warning System for Tipping Points in the Ocean

A team of scientists and other experts is investigating the mechanics of sudden, dramatic changes in our oceans. That should help us to avoid these tipping points—or to recover once they’ve been crossed.

In the summer of 1972, Hurricane Agnes swept up the East Coast of the United States. It was at the time the costliest hurricane in the U.S. history, and among the many things it damaged was the Chesapeake Bay. The storm flooded the watershed and sent a pulse of nutrient pollution—mainly nitrogen and phosphorous that ran off from farms and towns—streaming into the Bay.

Nutrient pollution is a problem in many estuaries because it can cause algal blooms that rob the water of oxygen and produce coastal dead zones. Until that storm the Chesapeake had managed to absorb the nutrients that ran off its fast developing watershed. But the pulse of pollution following Hurricane Agnes wiped out most of the seagrass in the Bay, precisely the plants that until then had absorbed the excess nutrients. As a result, even after pollution returned to pre-storm levels the Bay remained impaired.

Hurricane Agnes had pushed the Chesapeake past a tipping point—a threshold that triggers an abrupt and dramatic change—and there would be no turning back. These days up to one-quarter of the volume of the Chesapeake Bay is a dead zone every summer (though there are signs that the situation might be improving).

It is very difficult to identify tipping points in advance because the factors that contribute to them can be staggeringly complex. But the benefit of being aware of them is huge—a chance to change course or adapt before it’s too late. That’s why a team of researchers from NOAA Fisheries and several partner institutions is embarking on a four-year research project to understand the mechanics of tipping points in ocean ecosystems and to develop methods for identifying and dealing with them.

The Ocean Tipping Points Project includes scientists and other experts from NOAA Fisheries, University of California at Santa Barbara, Stanford University, and Environmental Defense Fund. The Project is just getting off the ground with a recent $3.1 million grant from the Gordon and Betty Moore Foundation.

"What we're trying to do is put up some warning signs on the road to a tipping point," said Phil Levin, a biologist at NOAA's Northwest Fisheries Science Center. In many respects decision-makers today are driving blind. "We hope to give them some practical tools they can use to slow down or change course before it’s too late."

An early warning is critical because once a tipping point is crossed, it can be extremely difficult to go back, as the situation in the Chesapeake demonstrates.

Scientists sometimes see “flickering” as an early warning sign of an approaching tipping point. "You see brief flashes of what the system will look like once you cross the tipping point, but then the system quickly reverts," said Jameal Samhouri, a NOAA ecologist working on the project. If the rate of flickering increases, that might be a sign that one of the upcoming flickers will stick and that the system will fail to flicker back.

Some tipping points will inevitably still take us by surprise, however, and understanding how they work might help us to recover after they’ve been crossed. For instance, when restoring habitat or rebuilding the population of an endangered species, we want to tip things in the direction we prefer. In that case, early warning recovery indicators might let us know what management actions are working and when there’s enough momentum in the system that it will tip on its own.

The Ocean Tipping Points Project has selected two case study sites, one in the Hawaiian Islands and the other in Haida Gwaii, an archipelago on the coast of British Columbia, where they will study tipping points in the ocean ecosystem. Just as importantly, they will also study socioeconomic tipping points in the communities that depend on the fish, tourism, and other resources that the ocean provides. That’s why in addition to ecologists the project team includes social scientists and legal and policy experts.

"First we need to identify leading indicators in specific ecosystems,” said Samhouri. Like statistical blips on a radar screen, these indicators might warn that a tipping point is nearby. "Then we will test whether those indicators can be transferred to other parts of the world."

In Haida Gwaii, for instance, herring are a vital species both for the fishermen that harvest their roe and for the marine mammals and seabirds that feed on them. By analyzing historic data and by working with local communities, researchers hope to identify leading indicators for tipping points related to herring. The big question will be whether those indicators can be usefully applied in other places with similar ecosystem dynamics. For example, in parts of Haida Gwaii, seasonal coastal upwelling brings nutrient-rich waters to the surface that fuel an outburst of marine life. Will indicators for herring in Haida Gwaii prove useful in other coastal upwelling zones such as along the coast of California or Peru?

Developing tipping point indicators is key from a socioeconomic perspective as well. In the United States, if a stock is overfished, the law requires that fishing pressure drop so the fish population can recover. Reduced catch limits can force some fishermen out of business. This process might pass a socioeconomic tipping point from which the industry cannot easily recover even when fish become abundant again.

“When you close down a fishery you lose more than just the boats and processing plants and jobs,” said Levin. "You also lose the knowledge of how to catch that fish, and you lose a cultural continuity that has helped fishing communities to survive." That is as true among the subsistence fishermen of Haida Gwaii as it is among the groundfishermen of New England.

In some cases, even after fishing pressure is reduced, fish populations fail to bounce back. This might be happening now with cod in the Northwest Atlantic. There are many theories about why cod are not rebounding, none of them yet conclusively proven. Climate change might be having an impact or food web dynamics might have shifted against them. But this much is certain: small fish populations are more vulnerable than healthy ones to random events like storms or unusual temperatures.

“One possibility is that we've pushed the stock over a threshold," said Levin. Knowing the mechanisms at work in this type of tipping point might help us to pull the species back over to the other side.