Last summer NCAR issued a dramatic press release announcing that oil from the Gulf spill would soon be appearing on the beaches of the Atlantic ocean. I discussed it here.
Here are the first four paragraphs of that press release:
BOULDER—A detailed computer modeling study released today indicates that oil from the massive spill in the Gulf of Mexico might soon extend along thousands of miles of the Atlantic coast and open ocean as early as this summer. The modeling results are captured in a series of dramatic animations produced by the National Center for Atmospheric Research (NCAR) and collaborators.A few weeks ago NCAR's David Hosansky who presumably wrote that press release, asks whether NCAR got it wrong. His answer? No, not really:
The research was supported in part by the National Science Foundation, NCAR’s sponsor. The results were reviewed by scientists at NCAR and elsewhere, although not yet submitted for peer-review publication.
“I’ve had a lot of people ask me, ‘Will the oil reach Florida?’” says NCAR scientist Synte Peacock, who worked on the study. “Actually, our best knowledge says the scope of this environmental disaster is likely to reach far beyond Florida, with impacts that have yet to be understood.”
The computer simulations indicate that, once the oil in the uppermost ocean has become entrained in the Gulf of Mexico’s fast-moving Loop Current, it is likely to reach Florida's Atlantic coast within weeks. It can then move north as far as about Cape Hatteras, North Carolina, with the Gulf Stream, before turning east. Whether the oil will be a thin film on the surface or mostly subsurface due to mixing in the uppermost region of the ocean is not known.
During last year’s crisis involving the massive release of oil into the Gulf of Mexico, NCAR issued a much-watched animation projecting that the oil could reach the Atlantic Ocean. But detectable amounts of oil never made it to the Atlantic, at least not in an easily visible form on the ocean surface. Not surprisingly, we’ve heard from a few people asking whether NCAR got it wrong.What then went wrong?
These events serve as a healthy reminder of a couple of things:
*the difference between a projection and an actual forecast
*the challenges of making short-term projections of natural processes that can act chaotically, such as ocean currents
First, the projection. Scientists from NCAR, the Department of Energy’s Los Alamos National Laboratory, and IFM-GEOMAR in Germany did not make a forecast of where the oil would go. Instead, they issued a projection. While there’s not always a clear distinction between the two, forecasts generally look only days or hours into the future and are built mostly on known elements (such as the current amount of humidity in the atmosphere). Projections tend to look further into the future and deal with a higher number of uncertainties (such as the rate at which oil degrades in open waters and the often chaotic movements of ocean currents).So who was at fault? According to Hosansky it was those dummies in the media:
Aware of the uncertainties, the scientific team projected the likely path of the spill with a computer model of a liquid dye. They used dye rather than actual oil, which undergoes bacterial breakdown, because a reliable method to simulate that breakdown was not available. As it turned out, the oil in the Gulf broke down quickly due to exceptionally strong bacterial action and, to some extent, the use of chemical dispersants.
Second, the challenges of short-term behavior. The Gulf's Loop Current acts as a conveyor belt, moving from the Yucatan through the Florida Straits into the Atlantic. Usually, the current curves northward near the Louisiana and Mississippi coasts—a configuration that would have put it on track to pick up the oil and transport it into open ocean. However, the current’s short-term movements over a few weeks or even months are chaotic and impossible to predict. Sometimes small eddies, or mini-currents, peel off, shifting the position and strength of the main current.
To determine the threat to the Atlantic, the research team studied averages of the Loop Current’s past behavior in order to simulate its likely course after the spill and ran several dozen computer simulations under various scenarios. Fortunately for the East Coast, the Loop Current did not behave in its usual fashion but instead remained farther south than usual, which kept it far from the Louisiana and Mississippi coast during the crucial few months before the oil degraded and/or was dispersed with chemical treatments.
The Loop Current typically goes into a southern configuration about every 6 to 19 months, although it rarely remains there for very long. NCAR scientist Synte Peacock, who worked on the projection, explains that part of the reason the current is unpredictable is “no two cycles of the Loop Current are ever exactly the same." She adds that the cycles are influenced by such variables as how large the eddy is, where the current detaches and moves south, and how long it takes for the current to reform.
Computer models can simulate the currents realistically, she adds. But they cannot predict when the currents will change over to a new cycle.
The scientists were careful to explain that their simulations were a suite of possible trajectories demonstrating what was likely to happen, but not a definitive forecast of what would happen. They reiterated that point in a peer-reviewed study on the simulations that appeared last August in Environmental Research Letters.
These caveats, however, got lost in much of the resulting media coverage.Another perspective is that having some of these caveats in the press release might have been a good idea.