Stu,
The central heating analogy isn't perfect but the purpose was to illustrate just how effective is warm water in heating the air above or around it.
Gandalf's point about the effect of 500 years of high solar activity raising the input to the Thermohaline Circulation yet being completely diffused in the journey along the circuit doesn't work because the THC retains its integrity along the entire track without being totally diffused along the way.
So there is a 'pipe' of sorts.
It is inconceivable that 500 year cycling of solar input to the oceans will not impose some temperature fluctuations along the 1000 to 1500 year route of the THC.
Then you said:
"Also relevant is the fact that the only way energy actually gets into and out of the Earth system is by radiation, which CO2 affects"
Well we know that so the sun isn't unlike a central heating boiler which also provides a single source of energy input. The reference to CO2 is not appropriate because the energy from more CO2 is entirely in the infra red which does not penetrate the oceans significantly if at all. Solar shortwave however gets in up to 200 meters so solar variability has a large effect but CO2 does not.
Stephen, I have done a little research on this...
The THC moves at around 250 miles per day....
I'll leave you and others to do the maths but your assertions don't stack up... The circulation is measured in a few tens of years not 1,000 to 1,500.
For your timescales the water has to travel a quarter of a million miles at least.
GTW, where'd you get this info? The fastest part of the THC is probably the Gulf stream, which reaches 5.6mph or 134.4 miles per day. The deep water just inches along much more slowly than this.
No, I think the main argument against serious coherence in the signal (I do figure at least some of the characterists of upwelling water are linked to what the world was like when it entered the deep water circulation) is not the speed of the conveyor but the fact that it splits:
So a climatic signal would emerge at different times at different places, another source of incoherence.