And if some of the sulphur manages to get into the atmosphere as aerosols, they will reduce solar influx and thus reduce global warming. This is actually a proposed method of inducing "global dimming".
Stratospheric sulfate aerosols (geoengineering) - Wikipedia, the free encyclopedia
The wiki article mentions a past and very big volcano eruption (Mount Pinatubo) as reference for an amount of sulphur to put into the atmosphere (20 million tons of SO2). About one third of this SO2 is sulphur (~million tons).
The cited amount of 7.29 million barrels a day equals ~1.1 million metric tons of oil. Assuming #6 oil with a worst case sulphur content of 3% by weight, gives 1.1 * 0.03 * 365 = 12 million tons of sulphur per year from shipping. This corresponds to a little more than a big volcano eruption.
How much of this actually makes it high enough up in the atmosphere to count, I don't know.
So, "we" may have basically already implemented the global dimming... (if my math and assumptions are correct)