A widely publicized Washington Post story, which even made the Atlantic Salmon Federation newsletter, says the Atlantic ocean conveyor belt, also known as the Atlantic Meridional Overturning Circulation (AMOC) is slowing down due to global warming. And since, according to the story, the AMOC drives the Gulf Stream that keeps Europe relatively mild, a slowing AMOC will cause Europe to cool, which would be bad. Except that every other story about Europe says it is warming, and warming is bad. Curiously the story doesn’t say that Europe actually is cooling, but still insists that the AMOC is slowing. Though the new study doesn’t rely on direct measurements, only indirect proxies, of which most but not all say the AMOC is slowing. Not only that but so does Michael Mann, who chimed in to point out that he predicted a slowing AMOC a few years ago so naturally he agrees with the new study. Although the story doesn’t mention the other study of the AMOC that came out the week previous, that used direct measurements in a statistical model instead of proxies and found that the AMOC isn’t slowing down at all. But it didn’t have a splashy press release so it must be wrong.
As you recall, Mann and some coauthors recently said basically there are no climate cycles, more specifically there is no AMO or Atlantic Multidecadal Oscillation. There is, however, an AMOC, and it is getting weaker. Or it might be, depending on which study crosses your desk. The one that Mann commented on says not only is it slowing but it’s responsible for a “cold blob” in the North Atlantic. So the slowing of the AMOC due to warming portends cooling not warming. After mentioning “The Day After Tomorrow” and a warning from the late Wallace Broeker that if the AMOC turns off we could be in the deep freeze in a hurry, it says “Scientists do not expect anything so severe in our future, especially because greenhouse gases will continue to cause offsetting warming.”
Or because the idea that the AMOC drives the Gulf stream might be exactly backwards. Many oceanographers think the Gulf Stream creates the AMOC not the other way around, that and it can’t shut down as long as the world turns and the winds blow. Or as MIT’s Carl Wunsch put it in a letter to Nature in 2004,
European readers should be reassured that the Gulf Stream's existence is a consequence of the large-scale wind system over the North Atlantic Ocean, and of the nature of fluid motion on a rotating planet. The only way to produce an ocean circulation without a Gulf Stream is either to turn off the wind system, or to stop the Earth's rotation, or both… The occurrence of a climate state without the Gulf Stream any time soon — within tens of millions of years — has a probability of little more than zero.
The alternative theory, that the AMOC drives the winds and the AMOC is slowing due to global warming, notwithstanding the data that says it hasn’t slowed down, means Europe must be cooling, except that the cooling is cleverly hidden by warming. So warming could cause cooling, and trigger a long-term trend going on since… never mind.
Let us not seem to sneer at oceans like Marvin the Paranoid Android. On the contrary, we have the greatest respect for them, both as scenery and as vast elemental objects capable of, well, absorbing a lot of CO2 and heat and stuff. In fact, as Boris Winterhalter recently argued on Watt’s Up With That, the IPCC is digging in the wrong place when it fixates on CO2 in the atmosphere. What makes Earth the place it is, he says, is paradoxically the water that covers most of it, and it is that water that is the main GHG.
“My guess is that many climate researchers have been misled by the flood of research projects developing extremely complicated climate models based on assumptions that global climate responds to changes in atmospheric carbon dioxide. This error has caused tremendous loss of money and manpower without actually being able to solve the question how Earth has succeeded in keeping global climate conducive to the various life forms that have inhabited our wonderful planet. My answer is WATER!”
So if ocean currents are real, and not just us messing with the bathwater, and if they have a major impact on climate, and operate over long periods of time with unpredictable, even non-linear trends, just possibly the science is not settled.