"Iron is the sixth most abundant element in the Universe, formed as the final act of nucleosynthesis, by silicon fusing in massive stars. While it makes up about 5% of the Earth's crust, the Earth's core is believed to consist largely of an iron-nickel alloy constituting 35% of the mass of the Earth as a whole. Iron is consequently the most abundant element on Earth, but only the fourth most abundant element in the Earth's crust.[4] Most of the iron in the crust is found combined with oxygen as iron oxide minerals such as hematite and magnetite."
I don't think it is too much of a stretch to say that a magnetic element that is 35 times more prevalent in earth's crust than water and which rides on top of a core that is 35% iron-nickel contributes more to our magnetic field than do ocean currents.
I'm inclined to agree with other posters who see this theory as a new line of attack in the global warming "debate"
My retort is that the earth has had numerous ice ages and warming spells, and the ice caps have formed and melted manifold times, disrupting ocean currents, yet the earth has always seemed to muddle through somehow.
In response to your closing, I don't see it as hopeful, except in the sense that the scientists proposing this theory are "hoping" for some of my taxpayer dollars to fund additional "research". In most societies, prostitution is illegal; in all, it is immoral...YMMV ;)
Way before approaching the depths where the core is molten, iron would be above it’s curie temperature and would no longer be magnetic.