You cannot seriously argue that the crude split in the Gulf could materially alter the viscosity of the water in the Gulf stream?
No! You are misquoting. The area under consideration is a very small part of the overall oceanic flows. Don't use larger examples to hide the much smaller example we have here. The gulf stream is the bit that comes near our shores but is not the whole answer to our weather patterns.
The suggestion is that we don't need to do so much damage before the system alters a small amount. We know (or in a lot of cases, don't know) that there can be ongoing changes caused by even small changes.
The simple effect of melting snow from an area and thus reducing the light reflected simply accelerates the temperature change (rise) because more solar energy is absorbed (the albedo effect - where fresh snow reflects away about 90% of the visible solar energy whereas bare soil absorbs around 80% of the incident radiation).
No worries, we will all likely be long gone before the results of our follies become apparent to our childrens' children's children in their old age.
Although it didn't take so long to destroy a large part of the protective ozone layer, did it? The Ausralians, in particular, are reaping that particular 'harvest'.
I never trivialise the acivities of humans - it is often for gain of wealth, not for the health of the planet. This particular event was of a similar ilk, but one that went horribly wrong, some are saying unecessarily. But that is another discussion.
Regards, RAB