Yet another paper and news cycle sounds the death knell, or more properly the passing bell, for the Atlantic Meridional Overturning Circulation. And if you’re not accustomed to running AMOC, well, it is something we’d miss when it’s gone. Reuters warned that “The Atlantic Ocean's current system, an engine of the Northern Hemisphere’s climate, could be weakening to such an extent that it could soon bring big changes to the world's weather, a scientific study said on Thursday.” And what’s apparently happening is that “As the atmosphere warms due to increased greenhouse gas emissions, the surface ocean beneath retains more of heat”, weakening the AMOC and pushing it toward an irreversible tipping point where “it would increase cooling of the Northern Hemisphere, sea level rise in the Atlantic, an overall fall in precipitation over Europe and North America and a shift in monsoons in South America and Africa, Britain's Met Office said.” Before you panic, we have heard this scare story long before, and we even made a video about it. And before you panic note also that the Reuters piece immediately added “Other climate models have said the AMOC will weaken over the coming century but that a collapse before 2100 is unlikely.” Still, time to panic! Right?
Obviously we actually have no idea what’s going to happen. And to say that not everyone is impressed by this study and its predictions is an understatement. Ocean currents like many other climate features are “non-linear,” that is their behaviour including transitions is “Sensitively Dependent on Initial Conditions” that cannot be measured with sufficient precision to enter them into models that depend on linear algebra to get close-enough outputs based on close-enough inputs. Which is not to knock linear algebra; it is part of the tool-kit that built the modern world including a lot of technology that works wonders. But there are things it can’t do.
Still, if we had an idea it wouldn’t be this one. The idea that warming the air could warm the water so much that the water cools the air irreversibly is silly. Cooler air would presumably cool the oceans, once all the complex interactive feedbacks have settled down if they ever do, and if this mechanism works anything like the way the story claims, it ought to reverse the warming process and, you’d suppose, crank the AMOC up again. Likewise, the fact that this current has been weakening for a century rather rules out human agency as the trigger, unless you subscribe to the fever-swamp climate-alarmist beliefs that (a) the effects of global warming kicked in at different times depending which scare you’re currently hyping and (b) if an effect has been going on for a long time it’s sound science to say the cause suddenly changed with no measurable impact on the outcome.
Not to mention that irreversible warming can cause irreversible cooling.