Problems if the Ash is Long term worldwide

http://www.kwintessential.co.uk/articles/article/Iceland/Laki-Volcano-Eruption-Iceland/529

quote below from above site on historical Iceland eruption.

Iceland is a country of volcanoes and one of the greatest eruptions has been via the Laki volcano in 1783.

Iceland is an island of volcanoes spreading right across its landscape and even extending beneath the sea. Many of the volcanoes of Iceland have erupted and been active during its history. In Iceland’s most recent history the massive eruption of the Laki volcano in 1783 caused one of the greatest disasters in living history.
The Laki volcano eruption occurred in the June of 1783 in Iceland killing many thousands and spreading a massive haze that covered most of Europe and parts of North America. This cloud was even reported to have extended into Asia and North Africa.
In its wake, the Laki Volcano eruption, although beginning in Iceland created widespread famine across Europe when the weather pattern changed so dramatically that it affected vital crops in the summer months and saw the loss of livestock.

End quote:

So the real problem is that jets around the world might not be able to fly for sometime depending upon how long these ash clouds continue to erupt out of the volcanoes there. This could continue theoretically for a long time like 6 months to a year. This could be disastrous for not only Europe but the entire world economy. If Europe can't fly jets or grow food this could be very difficult for many people worldwide.

Another problem is that an ash cloud this big is going to travel to England and Europe but because of the jet stream it will then travel across Europe to Russia and China and then across the Pacific to the Americas. So this sort of thing could theoretically ground most of the jets in the northern hemisphere eventually to the point where high speed trains, Ships and cars might be the only safe alternative to jets worldwide for a time.