Conveyor Belt Model Broken
News has come that the famed ocean conveyor belt, subject of countless TV documentaries and science lessons, is not as simple as scientists believed. The 50 year old model of global ocean circulation that predicts a deep Atlantic counter current below the Gulf Stream has been called into question by an armada of drifting subsurface sensors. As shocking as this news is to oceanographers it is even worse for climate modelers—it means that all the current climate prediction models are significantly wrong.
It is known by many names: the meridional overturning current (MOC), the thermohaline circulation (THC), and, popularly, the great ocean conveyor belt. It has been the subject of study by oceanographers for half a century and is known to be a fundamentally important part of earthly climate regulation. It is the primary mechanism for transferring heat from the tropics to higher latitudes, the proximate reason that the occasional palm tree grows on the south coast of England. Until now, scientists thought they had a pretty good handle on how the current flows, the mechanisms that drive the circulation and affect climate world wide.
A new report by Amy Bower of Wood’s Hole and Susan Lozier of Duke University et al., to be published in a forthcoming issue of Nature, has rocked the climate community's complacency. A bevy of subsurface RAFOS floats, drifting 2200 – 4900 feet (700 – 1500 m) deep, have shown several fundamental assumptions about the structure of the current to be wrong. RAFOS floats (SOFAR spelled backward) are floating instruments designed to move with the water and track the water's movements. It seems that 75% of the RAFOS floats escaped the Deep Western Boundary Current (DWBC) and drifted into open ocean. Only 8% of the RAFOS floats followed the DWBC conveyor belt current, according to the Nature report.
Track of a float crossing the North Atlantic Current (top) with corresponding temperature and pressure records (bottom). Courtesy of the RAFOS Float Group at University of Rhode Island.
This confirms suspicions that that first began surfacing in the 1990’s, that things were not quit as neat and simple as oceanographers had thought. Earlier observations had led to the widely held view that the DWBC is the dominant pathway for the export of cold Labrador Sea Water (LSW) from its formation site in the northern North Atlantic towards the Equator. The new findings indicate that instead of the single, orderly current flow previously envisioned, the conveyor belt is actually comprised of many slower, more variable and possibly wandering eddies in the interior ocean. Quoting from the report:
Here we show that most of the recently ventilated LSW entering the subtropics follows interior, not DWBC, pathways. The interior pathways are revealed by trajectories of subsurface RAFOS floats released during the period 2003–2005 that recorded once-daily temperature, pressure and acoustically determined position for two years, and by model-simulated 'e-floats' released in the subpolar DWBC. The evidence points to a few specific locations around the Grand Banks where LSW is most often injected into the interior. These results have implications for deep ocean ventilation and suggest that the interior subtropical gyre should not be ignored when considering the Atlantic meridional overturning circulation.
Triggered by a bunch of drifting ocean monitoring instruments, this new revelation represents a major paradigm shift in ocean circulation theory. Even more dramatic is the impact on current ocean circulation models, major components of the general circulation models (GCM) used to predict climate change. To understand how global climate changes in response to natural and human generated changes, it is essential to determine how quickly and by what pathways climate change signals are transported throughout the global ocean. Ocean currents not only redistribute surface warmth, the oceans themselves are a vast reservoir for heat and carbon dioxide, affecting both short term and long term climate change.
“Everybody always thought this deep flow operated like a conveyor belt, but what we are saying is that concept doesn't hold anymore,” said Duke oceanographer Susan Lozier. “So it's going to be more difficult to measure these climate change signals in the deep ocean.”
This has been a particularly disquieting week for the climate change establishment, with new discoveries regarding the importance of aerosols' impact on sea surface temperatures (SST) and cloud formation, and the halving of predicted sea-level increases due to ice sheet melting coupled with predictions of significant change in Earth's gravity field and rotational axis if Antarctica even partially melts. Add the news regarding the THC and one has to ask, how many revelations of erroneous assumptions are necessary before climate modelers admit that their computer programs are incapable of accurately predicting future climate change?
Climate skeptics are sometimes accused of selectively interpreting scientific data in order to bolster their case against anthropogenic global warming (AGW). The term used is “cherry picking.” When a theory makes certain predictions it is totally acceptable, even obligatory, to investigate those predictions. When a theory is based on certain fundamental assumptions regarding underlying science it is perfectly logical to question that theory when its underlying assumptions are shown to be in error. This is not cherry picking, it is how science works. It may discomfort those who complacently believe in the “consensus view” of AGW, but that is of no importance to science.
In this blog I have showcased a dozen or more scientific papers that end with a statement saying “the climate models need to take this into account,” or words to that effect. Time after time the theory of global warming and the models it rests on have been shown to be lacking. Sometimes in small ways, sometimes in large, fundamental ways (as is the case here) holes in the AGW theory keep appearing. The IPCC and the climate modeling crowd have constructed complex models of a chaotic system based on incomplete and erroneous assumptions—they have built a house of cards and asked us all to move in without checking the soundness of the foundation. Thankfully, anthropogenic global warming is dying the death of a thousand cuts—this is often the fate of flawed theories.
Be safe, enjoy the interglacial and stay skeptical.
Early prototype floating ocean monitors.